libpthread-301.30.1.tar.gz

[apple/libpthread.git] / kern / kern_synch.c

/*
 * Copyright (c) 2000-2012 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/* Copyright (c) 1995-2005 Apple Computer, Inc. All Rights Reserved */
/*
 *      pthread_support.c
 */

#include <sys/param.h>
#include <sys/queue.h>
#include <sys/resourcevar.h>
//#include <sys/proc_internal.h>
#include <sys/kauth.h>
#include <sys/systm.h>
#include <sys/timeb.h>
#include <sys/times.h>
#include <sys/time.h>
#include <sys/acct.h>
#include <sys/kernel.h>
#include <sys/wait.h>
#include <sys/signalvar.h>
#include <sys/syslog.h>
#include <sys/stat.h>
#include <sys/lock.h>
#include <sys/kdebug.h>
//#include <sys/sysproto.h>
//#include <sys/pthread_internal.h>
#include <sys/vm.h>
#include <sys/user.h>

#include <mach/mach_types.h>
#include <mach/vm_prot.h>
#include <mach/semaphore.h>
#include <mach/sync_policy.h>
#include <mach/task.h>
#include <kern/kern_types.h>
#include <kern/task.h>
#include <kern/clock.h>
#include <mach/kern_return.h>
#include <kern/thread.h>
#include <kern/sched_prim.h>
#include <kern/thread_call.h>
#include <kern/kalloc.h>
#include <kern/zalloc.h>
#include <kern/sched_prim.h>
#include <kern/processor.h>
#include <kern/block_hint.h>
//#include <kern/mach_param.h>
#include <mach/mach_vm.h>
#include <mach/mach_param.h>
#include <mach/thread_policy.h>
#include <mach/message.h>
#include <mach/port.h>
//#include <vm/vm_protos.h>
#include <vm/vm_map.h>
#include <mach/vm_region.h>

#include <libkern/OSAtomic.h>

#include <pexpert/pexpert.h>
#include <sys/pthread_shims.h>

#include "kern_internal.h"
#include "synch_internal.h"
#include "kern_trace.h"

typedef struct uthread *uthread_t;

//#define __FAILEDUSERTEST__(s) do { panic(s); } while (0)
#define __FAILEDUSERTEST__(s) do { printf("PSYNCH: pid[%d]: %s\n", proc_pid(current_proc()), s); } while (0)

#define ECVCERORR       256
#define ECVPERORR       512

lck_mtx_t *pthread_list_mlock;

#define PTH_HASHSIZE 100

static LIST_HEAD(pthhashhead, ksyn_wait_queue) *pth_glob_hashtbl;
static unsigned long pthhash;

static LIST_HEAD(, ksyn_wait_queue) pth_free_list;

static zone_t kwq_zone; /* zone for allocation of ksyn_queue */
static zone_t kwe_zone; /* zone for allocation of ksyn_waitq_element */

#define SEQFIT 0
#define FIRSTFIT 1

struct ksyn_queue {
        TAILQ_HEAD(ksynq_kwelist_head, ksyn_waitq_element) ksynq_kwelist;
        uint32_t        ksynq_count;            /* number of entries in queue */
        uint32_t        ksynq_firstnum;         /* lowest seq in queue */
        uint32_t        ksynq_lastnum;          /* highest seq in queue */
};
typedef struct ksyn_queue *ksyn_queue_t;

enum {
        KSYN_QUEUE_READ = 0,
        KSYN_QUEUE_WRITER,
        KSYN_QUEUE_MAX,
};

struct ksyn_wait_queue {
        LIST_ENTRY(ksyn_wait_queue) kw_hash;
        LIST_ENTRY(ksyn_wait_queue) kw_list;
        user_addr_t kw_addr;
        uint64_t kw_owner;
        uint64_t kw_object;             /* object backing in shared mode */
        uint64_t kw_offset;             /* offset inside the object in shared mode */
        int     kw_pflags;              /* flags under listlock protection */
        struct timeval kw_ts;           /* timeval need for upkeep before free */
        int     kw_iocount;             /* inuse reference */
        int     kw_dropcount;           /* current users unlocking... */
        
        int     kw_type;                /* queue type like mutex, cvar, etc */
        uint32_t kw_inqueue;            /* num of waiters held */
        uint32_t kw_fakecount;          /* number of error/prepost fakes */
        uint32_t kw_highseq;            /* highest seq in the queue */
        uint32_t kw_lowseq;             /* lowest seq in the queue */
        uint32_t kw_lword;              /* L value from userland */
        uint32_t kw_uword;              /* U world value from userland */
        uint32_t kw_sword;              /* S word value from userland */
        uint32_t kw_lastunlockseq;      /* the last seq that unlocked */
        /* for CV to be used as the seq kernel has seen so far */
#define kw_cvkernelseq kw_lastunlockseq
        uint32_t kw_lastseqword;                /* the last seq that unlocked */
        /* for mutex and cvar we need to track I bit values */
        uint32_t kw_nextseqword;        /* the last seq that unlocked; with num of waiters */
        uint32_t kw_overlapwatch;       /* chance for overlaps */
        uint32_t kw_pre_rwwc;           /* prepost count */
        uint32_t kw_pre_lockseq;        /* prepost target seq */
        uint32_t kw_pre_sseq;           /* prepost target sword, in cvar used for mutexowned */
        uint32_t kw_pre_intrcount;      /* prepost of missed wakeup due to intrs */
        uint32_t kw_pre_intrseq;        /* prepost of missed wakeup limit seq */
        uint32_t kw_pre_intrretbits;    /* return bits value for missed wakeup threads */
        uint32_t kw_pre_intrtype;       /* type of failed wakueps*/
        
        int     kw_kflags;
        int             kw_qos_override;        /* QoS of max waiter during contention period */
        struct ksyn_queue kw_ksynqueues[KSYN_QUEUE_MAX];        /* queues to hold threads */
        lck_mtx_t kw_lock;              /* mutex lock protecting this structure */
};
typedef struct ksyn_wait_queue * ksyn_wait_queue_t;

#define TID_ZERO (uint64_t)0

/* bits needed in handling the rwlock unlock */
#define PTH_RW_TYPE_READ        0x01
#define PTH_RW_TYPE_WRITE       0x04
#define PTH_RW_TYPE_MASK        0xff
#define PTH_RW_TYPE_SHIFT       8

#define PTH_RWSHFT_TYPE_READ    0x0100
#define PTH_RWSHFT_TYPE_WRITE   0x0400
#define PTH_RWSHFT_TYPE_MASK    0xff00

/*
 * Mutex pshared attributes
 */
#define PTHREAD_PROCESS_SHARED          _PTHREAD_MTX_OPT_PSHARED
#define PTHREAD_PROCESS_PRIVATE         0x20
#define PTHREAD_PSHARED_FLAGS_MASK      0x30

/*
 * Mutex policy attributes
 */
#define _PTHREAD_MUTEX_POLICY_NONE              0
#define _PTHREAD_MUTEX_POLICY_FAIRSHARE         0x040   /* 1 */
#define _PTHREAD_MUTEX_POLICY_FIRSTFIT          0x080   /* 2 */
#define _PTHREAD_MUTEX_POLICY_REALTIME          0x0c0   /* 3 */
#define _PTHREAD_MUTEX_POLICY_ADAPTIVE          0x100   /* 4 */
#define _PTHREAD_MUTEX_POLICY_PRIPROTECT        0x140   /* 5 */
#define _PTHREAD_MUTEX_POLICY_PRIINHERIT        0x180   /* 6 */
#define PTHREAD_POLICY_FLAGS_MASK               0x1c0

/* pflags */
#define KSYN_WQ_INHASH  2
#define KSYN_WQ_SHARED  4
#define KSYN_WQ_WAITING 8       /* threads waiting for this wq to be available */
#define KSYN_WQ_FLIST   0X10    /* in free list to be freed after a short delay */

/* kflags */
#define KSYN_KWF_INITCLEARED    1       /* the init status found and preposts cleared */
#define KSYN_KWF_ZEROEDOUT      2       /* the lword, etc are inited to 0 */
#define KSYN_KWF_QOS_APPLIED    4       /* QoS override applied to owner */

#define KSYN_CLEANUP_DEADLINE 10
static int psynch_cleanupset;
thread_call_t psynch_thcall;

#define KSYN_WQTYPE_INWAIT      0x1000
#define KSYN_WQTYPE_INDROP      0x2000
#define KSYN_WQTYPE_MTX         0x01
#define KSYN_WQTYPE_CVAR        0x02
#define KSYN_WQTYPE_RWLOCK      0x04
#define KSYN_WQTYPE_SEMA        0x08
#define KSYN_WQTYPE_MASK        0xff

#define KSYN_WQTYPE_MUTEXDROP   (KSYN_WQTYPE_INDROP | KSYN_WQTYPE_MTX)

#define KW_UNLOCK_PREPOST               0x01
#define KW_UNLOCK_PREPOST_READLOCK      0x08
#define KW_UNLOCK_PREPOST_WRLOCK        0x20

static void
CLEAR_PREPOST_BITS(ksyn_wait_queue_t kwq)
{
        kwq->kw_pre_lockseq = 0;
        kwq->kw_pre_sseq = PTHRW_RWS_INIT;
        kwq->kw_pre_rwwc = 0;
}

static void
CLEAR_INTR_PREPOST_BITS(ksyn_wait_queue_t kwq)
{
        kwq->kw_pre_intrcount = 0;
        kwq->kw_pre_intrseq = 0;
        kwq->kw_pre_intrretbits = 0;
        kwq->kw_pre_intrtype = 0;
}

static void
CLEAR_REINIT_BITS(ksyn_wait_queue_t kwq)
{
        if ((kwq->kw_type & KSYN_WQTYPE_MASK) == KSYN_WQTYPE_CVAR) {
                if (kwq->kw_inqueue != 0 && kwq->kw_inqueue != kwq->kw_fakecount) {
                        panic("CV:entries in queue durinmg reinit %d:%d\n",kwq->kw_inqueue, kwq->kw_fakecount);
                }
        };
        if ((kwq->kw_type & KSYN_WQTYPE_MASK) == KSYN_WQTYPE_RWLOCK) {
                kwq->kw_nextseqword = PTHRW_RWS_INIT;
                kwq->kw_overlapwatch = 0;
        };
        CLEAR_PREPOST_BITS(kwq);
        kwq->kw_lastunlockseq = PTHRW_RWL_INIT;
        kwq->kw_lastseqword = PTHRW_RWS_INIT;
        CLEAR_INTR_PREPOST_BITS(kwq);
        kwq->kw_lword = 0;
        kwq->kw_uword = 0;
        kwq->kw_sword = PTHRW_RWS_INIT;
}

static int ksyn_wq_hash_lookup(user_addr_t uaddr, proc_t p, int flags, ksyn_wait_queue_t *kwq, struct pthhashhead **hashptr, uint64_t *object, uint64_t *offset);
static int ksyn_wqfind(user_addr_t mutex, uint32_t mgen, uint32_t ugen, uint32_t rw_wc, int flags, int wqtype , ksyn_wait_queue_t *wq);
static void ksyn_wqrelease(ksyn_wait_queue_t mkwq, int qfreenow, int wqtype);
static int ksyn_findobj(user_addr_t uaddr, uint64_t *objectp, uint64_t *offsetp);

static int _wait_result_to_errno(wait_result_t result);

static int ksyn_wait(ksyn_wait_queue_t, int, uint32_t, int, uint64_t, thread_continue_t, block_hint_t);
static kern_return_t ksyn_signal(ksyn_wait_queue_t, int, ksyn_waitq_element_t, uint32_t);
static void ksyn_freeallkwe(ksyn_queue_t kq);

static kern_return_t ksyn_mtxsignal(ksyn_wait_queue_t, ksyn_waitq_element_t kwe, uint32_t);
static void ksyn_mtx_update_owner_qos_override(ksyn_wait_queue_t, uint64_t tid, boolean_t prepost);
static void ksyn_mtx_drop_qos_override(ksyn_wait_queue_t);

static int kwq_handle_unlock(ksyn_wait_queue_t, uint32_t mgen, uint32_t rw_wc, uint32_t *updatep, int flags, int *blockp, uint32_t premgen);

static void ksyn_queue_init(ksyn_queue_t kq);
static int ksyn_queue_insert(ksyn_wait_queue_t kwq, int kqi, ksyn_waitq_element_t kwe, uint32_t mgen, int firstfit);
static void ksyn_queue_remove_item(ksyn_wait_queue_t kwq, ksyn_queue_t kq, ksyn_waitq_element_t kwe);
static void ksyn_queue_free_items(ksyn_wait_queue_t kwq, int kqi, uint32_t upto, int all);

static void update_low_high(ksyn_wait_queue_t kwq, uint32_t lockseq);
static uint32_t find_nextlowseq(ksyn_wait_queue_t kwq);
static uint32_t find_nexthighseq(ksyn_wait_queue_t kwq);
static int find_seq_till(ksyn_wait_queue_t kwq, uint32_t upto, uint32_t nwaiters, uint32_t *countp);

static uint32_t ksyn_queue_count_tolowest(ksyn_queue_t kq, uint32_t upto);

static ksyn_waitq_element_t ksyn_queue_find_cvpreposeq(ksyn_queue_t kq, uint32_t cgen);
static void ksyn_handle_cvbroad(ksyn_wait_queue_t ckwq, uint32_t upto, uint32_t *updatep);
static void ksyn_cvupdate_fixup(ksyn_wait_queue_t ckwq, uint32_t *updatep);
static ksyn_waitq_element_t ksyn_queue_find_signalseq(ksyn_wait_queue_t kwq, ksyn_queue_t kq, uint32_t toseq, uint32_t lockseq);

static void psynch_cvcontinue(void *, wait_result_t);
static void psynch_mtxcontinue(void *, wait_result_t);

static int ksyn_wakeupreaders(ksyn_wait_queue_t kwq, uint32_t limitread, int allreaders, uint32_t updatebits, int *wokenp);
static int kwq_find_rw_lowest(ksyn_wait_queue_t kwq, int flags, uint32_t premgen, int *type, uint32_t lowest[]);
static ksyn_waitq_element_t ksyn_queue_find_seq(ksyn_wait_queue_t kwq, ksyn_queue_t kq, uint32_t seq);

static void
UPDATE_CVKWQ(ksyn_wait_queue_t kwq, uint32_t mgen, uint32_t ugen, uint32_t rw_wc)
{
        int sinit = ((rw_wc & PTH_RWS_CV_CBIT) != 0);
        
        // assert((kwq->kw_type & KSYN_WQTYPE_MASK) == KSYN_WQTYPE_CVAR);
        
        if ((kwq->kw_kflags & KSYN_KWF_ZEROEDOUT) != 0) {
                /* the values of L,U and S are cleared out due to L==S in previous transition */
                kwq->kw_lword = mgen;
                kwq->kw_uword = ugen;
                kwq->kw_sword = rw_wc;
                kwq->kw_kflags &= ~KSYN_KWF_ZEROEDOUT;
        } else {
                if (is_seqhigher(mgen, kwq->kw_lword)) {
                        kwq->kw_lword = mgen;
                }
                if (is_seqhigher(ugen, kwq->kw_uword)) {
                        kwq->kw_uword = ugen;
                }
                if (sinit && is_seqhigher(rw_wc, kwq->kw_sword)) {
                        kwq->kw_sword = rw_wc;
                }
        }
        if (sinit && is_seqlower(kwq->kw_cvkernelseq, rw_wc)) {
                kwq->kw_cvkernelseq = (rw_wc & PTHRW_COUNT_MASK);
        }
}

static void
pthread_list_lock(void)
{
        lck_mtx_lock(pthread_list_mlock);
}

static void
pthread_list_unlock(void)
{
        lck_mtx_unlock(pthread_list_mlock);
}

static void
ksyn_wqlock(ksyn_wait_queue_t kwq)
{
        
        lck_mtx_lock(&kwq->kw_lock);
}

static void
ksyn_wqunlock(ksyn_wait_queue_t kwq)
{
        lck_mtx_unlock(&kwq->kw_lock);
}


/* routine to drop the mutex unlocks , used both for mutexunlock system call and drop during cond wait */
static uint32_t
_psynch_mutexdrop_internal(ksyn_wait_queue_t kwq, uint32_t mgen, uint32_t ugen, int flags)
{
        kern_return_t ret;
        uint32_t returnbits = 0;
        int firstfit = (flags & PTHREAD_POLICY_FLAGS_MASK) == _PTHREAD_MUTEX_POLICY_FIRSTFIT;
        uint32_t nextgen = (ugen + PTHRW_INC);

        ksyn_wqlock(kwq);
        kwq->kw_lastunlockseq = (ugen & PTHRW_COUNT_MASK);
        uint32_t updatebits = (kwq->kw_highseq & PTHRW_COUNT_MASK) | (PTH_RWL_EBIT | PTH_RWL_KBIT);

redrive:
        if (firstfit) {
                if (kwq->kw_inqueue == 0) {
                        // not set or the new lock sequence is higher
                        if (kwq->kw_pre_rwwc == 0 || is_seqhigher(mgen, kwq->kw_pre_lockseq)) {
                                kwq->kw_pre_lockseq = (mgen & PTHRW_COUNT_MASK);
                        }
                        kwq->kw_pre_rwwc = 1;
                        ksyn_mtx_drop_qos_override(kwq);
                        kwq->kw_owner = 0;
                        // indicate prepost content in kernel
                        returnbits = mgen | PTH_RWL_PBIT;
                } else {
                        // signal first waiter
                        ret = ksyn_mtxsignal(kwq, NULL, updatebits);
                        if (ret == KERN_NOT_WAITING) {
                                goto redrive;
                        }
                }
        } else {        
                int prepost = 0;
                if (kwq->kw_inqueue == 0) {
                        // No waiters in the queue.
                        prepost = 1;
                } else {
                        uint32_t low_writer = (kwq->kw_ksynqueues[KSYN_QUEUE_WRITER].ksynq_firstnum & PTHRW_COUNT_MASK);
                        if (low_writer == nextgen) {
                                /* next seq to be granted found */
                                /* since the grant could be cv, make sure mutex wait is set incase the thread interrupted out */
                                ret = ksyn_mtxsignal(kwq, NULL, updatebits | PTH_RWL_MTX_WAIT);
                                if (ret == KERN_NOT_WAITING) {
                                        /* interrupt post */
                                        kwq->kw_pre_intrcount = 1;
                                        kwq->kw_pre_intrseq = nextgen;
                                        kwq->kw_pre_intrretbits = updatebits;
                                        kwq->kw_pre_intrtype = PTH_RW_TYPE_WRITE;
                                }
                                
                        } else if (is_seqhigher(low_writer, nextgen)) {
                                prepost = 1;
                        } else {
                                //__FAILEDUSERTEST__("psynch_mutexdrop_internal: FS mutex unlock sequence higher than the lowest one is queue\n");
                                ksyn_waitq_element_t kwe;
                                kwe = ksyn_queue_find_seq(kwq, &kwq->kw_ksynqueues[KSYN_QUEUE_WRITER], nextgen);
                                if (kwe != NULL) {
                                        /* next seq to be granted found */
                                        /* since the grant could be cv, make sure mutex wait is set incase the thread interrupted out */
                                        ret = ksyn_mtxsignal(kwq, kwe, updatebits | PTH_RWL_MTX_WAIT);
                                        if (ret == KERN_NOT_WAITING) {
                                                goto redrive;
                                        }
                                } else {
                                        prepost = 1;
                                }
                        }
                }
                if (prepost) {
                        ksyn_mtx_drop_qos_override(kwq);
                        kwq->kw_owner = 0;
                        if (++kwq->kw_pre_rwwc > 1) {
                                __FAILEDUSERTEST__("_psynch_mutexdrop_internal: multiple preposts\n");
                        } else {
                                kwq->kw_pre_lockseq = (nextgen & PTHRW_COUNT_MASK);
                        }
                }
        }
        
        ksyn_wqunlock(kwq);
        ksyn_wqrelease(kwq, 1, KSYN_WQTYPE_MUTEXDROP);
        return returnbits;
}

static int
_ksyn_check_init(ksyn_wait_queue_t kwq, uint32_t lgenval)
{
        int res = (lgenval & PTHRW_RWL_INIT) != 0;
        if (res) {
                if ((kwq->kw_kflags & KSYN_KWF_INITCLEARED) == 0) {
                        /* first to notice the reset of the lock, clear preposts */
                        CLEAR_REINIT_BITS(kwq);
                        kwq->kw_kflags |= KSYN_KWF_INITCLEARED;
                }
        }
        return res;
}

static int
_ksyn_handle_missed_wakeups(ksyn_wait_queue_t kwq,
                            uint32_t type,
                            uint32_t lockseq,
                            uint32_t *retval)
{
        int res = 0;
        if (kwq->kw_pre_intrcount != 0 &&
                kwq->kw_pre_intrtype == type &&
                (kwq->kw_pre_intrseq == 0 || is_seqlower_eq(lockseq, kwq->kw_pre_intrseq))) {
                kwq->kw_pre_intrcount--;
                *retval = kwq->kw_pre_intrretbits;
                if (kwq->kw_pre_intrcount == 0) {
                        CLEAR_INTR_PREPOST_BITS(kwq);
                }
                res = 1;
        }
        return res;
}

static int
_ksyn_handle_overlap(ksyn_wait_queue_t kwq,
                     uint32_t lgenval,
                     uint32_t rw_wc,
                     uint32_t *retval)
{
        int res = 0;

        // check for overlap and no pending W bit (indicates writers)
        if (kwq->kw_overlapwatch != 0 &&
            (rw_wc & PTHRW_RWS_SAVEMASK) == 0 &&
            (lgenval & PTH_RWL_WBIT) == 0) {
                /* overlap is set, so no need to check for valid state for overlap */

                if (is_seqlower_eq(rw_wc, kwq->kw_nextseqword) || is_seqhigher_eq(kwq->kw_lastseqword, rw_wc)) {
                        /* increase the next expected seq by one */
                        kwq->kw_nextseqword += PTHRW_INC;
                        /* set count by one & bits from the nextseq and add M bit */
                        *retval = PTHRW_INC | ((kwq->kw_nextseqword & PTHRW_BIT_MASK) | PTH_RWL_MBIT);
                        res = 1;
                }
        }
        return res;
}

static int
_ksyn_handle_prepost(ksyn_wait_queue_t kwq,
                     uint32_t type,
                     uint32_t lockseq,
                     uint32_t *retval)
{
        int res = 0;
        if (kwq->kw_pre_rwwc != 0 && is_seqlower_eq(lockseq, kwq->kw_pre_lockseq)) {
                kwq->kw_pre_rwwc--;
                if (kwq->kw_pre_rwwc == 0) {
                        uint32_t preseq = kwq->kw_pre_lockseq;
                        uint32_t prerw_wc = kwq->kw_pre_sseq;
                        CLEAR_PREPOST_BITS(kwq);
                        if ((kwq->kw_kflags & KSYN_KWF_INITCLEARED) != 0){
                                kwq->kw_kflags &= ~KSYN_KWF_INITCLEARED;
                        }

                        int error, block;
                        uint32_t updatebits;
                        error = kwq_handle_unlock(kwq, preseq, prerw_wc, &updatebits, (type|KW_UNLOCK_PREPOST), &block, lockseq);
                        if (error != 0) {
                                panic("kwq_handle_unlock failed %d\n", error);
                        }

                        if (block == 0) {
                                *retval = updatebits;
                                res = 1;
                        }
                }
        }
        return res;
}

/* Helpers for QoS override management. Only applies to mutexes */
static void ksyn_mtx_update_owner_qos_override(ksyn_wait_queue_t kwq, uint64_t tid, boolean_t prepost)
{
        if (!(kwq->kw_pflags & KSYN_WQ_SHARED)) {
                boolean_t wasboosted = (kwq->kw_kflags & KSYN_KWF_QOS_APPLIED) ? TRUE : FALSE;
                int waiter_qos = pthread_kern->proc_usynch_get_requested_thread_qos(current_uthread());
                
                kwq->kw_qos_override = MAX(waiter_qos, kwq->kw_qos_override);
                
                if (prepost && kwq->kw_inqueue == 0) {
                        // if there are no more waiters in the queue after the new (prepost-receiving) owner, we do not set an
                        // override, because the receiving owner may not re-enter the kernel to signal someone else if it is
                        // the last one to unlock. If other waiters end up entering the kernel, they will boost the owner
                        tid = 0;
                }
                
                if (tid != 0) {
                        if ((tid == kwq->kw_owner) && (kwq->kw_kflags & KSYN_KWF_QOS_APPLIED)) {
                                // hint continues to be accurate, and a boost was already applied
                                pthread_kern->proc_usynch_thread_qos_add_override_for_resource(current_task(), NULL, tid, kwq->kw_qos_override, FALSE, kwq->kw_addr, THREAD_QOS_OVERRIDE_TYPE_PTHREAD_MUTEX);
                        } else {
                                // either hint did not match previous owner, or hint was accurate but mutex was not contended enough for a boost previously
                                boolean_t boostsucceded;
                                
                                boostsucceded = pthread_kern->proc_usynch_thread_qos_add_override_for_resource(current_task(), NULL, tid, kwq->kw_qos_override, TRUE, kwq->kw_addr, THREAD_QOS_OVERRIDE_TYPE_PTHREAD_MUTEX);
                                
                                if (boostsucceded) {
                                        kwq->kw_kflags |= KSYN_KWF_QOS_APPLIED;
                                }

                                if (wasboosted && (tid != kwq->kw_owner) && (kwq->kw_owner != 0)) {
                                        // the hint did not match the previous owner, so drop overrides
                                        PTHREAD_TRACE(TRACE_psynch_ksyn_incorrect_owner, kwq->kw_owner, 0, 0, 0, 0);
                                        pthread_kern->proc_usynch_thread_qos_remove_override_for_resource(current_task(), NULL, kwq->kw_owner, kwq->kw_addr, THREAD_QOS_OVERRIDE_TYPE_PTHREAD_MUTEX);
                                }
                        }
                } else {
                        // new hint tells us that we don't know the owner, so drop any existing overrides
                        kwq->kw_kflags &= ~KSYN_KWF_QOS_APPLIED;
                        kwq->kw_qos_override = THREAD_QOS_UNSPECIFIED;

                        if (wasboosted && (kwq->kw_owner != 0)) {
                                // the hint did not match the previous owner, so drop overrides
                                PTHREAD_TRACE(TRACE_psynch_ksyn_incorrect_owner, kwq->kw_owner, 0, 0, 0, 0);
                                pthread_kern->proc_usynch_thread_qos_remove_override_for_resource(current_task(), NULL, kwq->kw_owner, kwq->kw_addr, THREAD_QOS_OVERRIDE_TYPE_PTHREAD_MUTEX);
                        }
                }
        }
}

static boolean_t
ksyn_mtx_transfer_qos_override_begin(ksyn_wait_queue_t kwq,
                ksyn_waitq_element_t kwe, uint64_t *kw_owner)
{
        boolean_t needs_commit = FALSE;
        if (!(kwq->kw_pflags & KSYN_WQ_SHARED)) {
                boolean_t wasboosted = (kwq->kw_kflags & KSYN_KWF_QOS_APPLIED) ? TRUE : FALSE;

                if (kwq->kw_inqueue > 1) {
                        boolean_t boostsucceeded;

                        // More than one waiter, so resource will still be contended after handing off ownership
                        boostsucceeded = pthread_kern->proc_usynch_thread_qos_add_override_for_resource(current_task(), kwe->kwe_uth, 0, kwq->kw_qos_override, TRUE, kwq->kw_addr, THREAD_QOS_OVERRIDE_TYPE_PTHREAD_MUTEX);

                        if (boostsucceeded) {
                                kwq->kw_kflags |= KSYN_KWF_QOS_APPLIED;
                        }
                } else {
                        // kw_inqueue == 1 to get to this point, which means there will be no contention after this point
                        kwq->kw_kflags &= ~KSYN_KWF_QOS_APPLIED;
                        kwq->kw_qos_override = THREAD_QOS_UNSPECIFIED;
                }

                // Remove the override that was applied to kw_owner. There may have been a race,
                // in which case it may not match the current thread
                if (wasboosted) {
                        if (kwq->kw_owner == 0) {
                                PTHREAD_TRACE(TRACE_psynch_ksyn_incorrect_owner, 0, 0, 0, 0, 0);
                        } else if (thread_tid(current_thread()) != kwq->kw_owner) {
                                PTHREAD_TRACE(TRACE_psynch_ksyn_incorrect_owner, kwq->kw_owner, 0, 0, 0, 0);
                                *kw_owner = kwq->kw_owner;
                                needs_commit = TRUE;
                        } else {
                                *kw_owner = 0;
                                needs_commit = TRUE;
                        }
                }
        }
        return needs_commit;
}

static void
ksyn_mtx_transfer_qos_override_commit(ksyn_wait_queue_t kwq, uint64_t kw_owner)
{
        struct uthread *uthread = kw_owner ? NULL : current_uthread();

        pthread_kern->proc_usynch_thread_qos_remove_override_for_resource(
                        current_task(), uthread, kw_owner, kwq->kw_addr,
                        THREAD_QOS_OVERRIDE_TYPE_PTHREAD_MUTEX);
}

static void ksyn_mtx_drop_qos_override(ksyn_wait_queue_t kwq)
{
        if (!(kwq->kw_pflags & KSYN_WQ_SHARED)) {
                boolean_t wasboosted = (kwq->kw_kflags & KSYN_KWF_QOS_APPLIED) ? TRUE : FALSE;
                
                // assume nobody else in queue if this routine was called
                kwq->kw_kflags &= ~KSYN_KWF_QOS_APPLIED;
                kwq->kw_qos_override = THREAD_QOS_UNSPECIFIED;
                
                // Remove the override that was applied to kw_owner. There may have been a race,
                // in which case it may not match the current thread
                if (wasboosted) {
                        if (kwq->kw_owner == 0) {
                                PTHREAD_TRACE(TRACE_psynch_ksyn_incorrect_owner, 0, 0, 0, 0, 0);
                        } else if (thread_tid(current_thread()) != kwq->kw_owner) {
                                PTHREAD_TRACE(TRACE_psynch_ksyn_incorrect_owner, kwq->kw_owner, 0, 0, 0, 0);
                                pthread_kern->proc_usynch_thread_qos_remove_override_for_resource(current_task(), NULL, kwq->kw_owner, kwq->kw_addr, THREAD_QOS_OVERRIDE_TYPE_PTHREAD_MUTEX);
                        } else {
                                pthread_kern->proc_usynch_thread_qos_remove_override_for_resource(current_task(), current_uthread(), 0, kwq->kw_addr, THREAD_QOS_OVERRIDE_TYPE_PTHREAD_MUTEX);
                        }
                }
        }
}

/*
 * psynch_mutexwait: This system call is used for contended psynch mutexes to block.
 */

int
_psynch_mutexwait(__unused proc_t p,
                  user_addr_t mutex,
                  uint32_t mgen,
                  uint32_t ugen,
                  uint64_t tid,
                  uint32_t flags,
                  uint32_t *retval)
{
        ksyn_wait_queue_t kwq;
        int error=0;
        int ins_flags;

        int firstfit = (flags & PTHREAD_POLICY_FLAGS_MASK) == _PTHREAD_MUTEX_POLICY_FIRSTFIT;
        uint32_t updatebits = 0;

        uint32_t lockseq = (mgen & PTHRW_COUNT_MASK);
        
        if (firstfit == 0) {
                ins_flags = SEQFIT;
        } else {
                /* first fit */
                ins_flags = FIRSTFIT;
        }
        
        error = ksyn_wqfind(mutex, mgen, ugen, 0, flags, (KSYN_WQTYPE_INWAIT|KSYN_WQTYPE_MTX), &kwq);
        if (error != 0) {
                return(error);
        }
        
        ksyn_wqlock(kwq);

        // mutexwait passes in an owner hint at the time userspace contended for the mutex, however, the
        // owner tid in the userspace data structure may be unset or SWITCHING (-1), or it may correspond
        // to a stale snapshot after the lock has subsequently been unlocked by another thread.
        if (tid == 0) {
                // contender came in before owner could write TID
                tid = 0;
        } else if (kwq->kw_lastunlockseq != PTHRW_RWL_INIT && is_seqlower(ugen, kwq->kw_lastunlockseq)) {
                // owner is stale, someone has come in and unlocked since this contended read the TID, so
                // assume what is known in the kernel is accurate
                tid = kwq->kw_owner;
        } else if (tid == PTHREAD_MTX_TID_SWITCHING) {
                // userspace didn't know the owner because it was being unlocked, but that unlocker hasn't
                // reached the kernel yet. So assume what is known in the kernel is accurate
                tid = kwq->kw_owner;
        } else {
                // hint is being passed in for a specific thread, and we have no reason not to trust
                // it (like the kernel unlock sequence being higher
        }

        
        if (_ksyn_handle_missed_wakeups(kwq, PTH_RW_TYPE_WRITE, lockseq, retval)) {
                ksyn_mtx_update_owner_qos_override(kwq, thread_tid(current_thread()), TRUE);
                kwq->kw_owner = thread_tid(current_thread());

                ksyn_wqunlock(kwq);
                goto out;
        }
        
        if ((kwq->kw_pre_rwwc != 0) && ((ins_flags == FIRSTFIT) || ((lockseq & PTHRW_COUNT_MASK) == (kwq->kw_pre_lockseq & PTHRW_COUNT_MASK) ))) {
                /* got preposted lock */
                kwq->kw_pre_rwwc--;
                if (kwq->kw_pre_rwwc == 0) {
                        CLEAR_PREPOST_BITS(kwq);
                        if (kwq->kw_inqueue == 0) {
                                updatebits = lockseq | (PTH_RWL_KBIT | PTH_RWL_EBIT);
                        } else {
                                updatebits = (kwq->kw_highseq & PTHRW_COUNT_MASK) | (PTH_RWL_KBIT | PTH_RWL_EBIT);
                        }
                        updatebits &= ~PTH_RWL_MTX_WAIT;
                        
                        if (updatebits == 0) {
                                __FAILEDUSERTEST__("psynch_mutexwait(prepost): returning 0 lseq in mutexwait with no EBIT \n");
                        }
                        
                        ksyn_mtx_update_owner_qos_override(kwq, thread_tid(current_thread()), TRUE);
                        kwq->kw_owner = thread_tid(current_thread());
            
                        ksyn_wqunlock(kwq);
                        *retval = updatebits;
                        goto out;
                } else {
                        __FAILEDUSERTEST__("psynch_mutexwait: more than one prepost\n");
                        kwq->kw_pre_lockseq += PTHRW_INC; /* look for next one */
                        ksyn_wqunlock(kwq);
                        error = EINVAL;
                        goto out;
                }
        }
        
        ksyn_mtx_update_owner_qos_override(kwq, tid, FALSE);
        kwq->kw_owner = tid;

        error = ksyn_wait(kwq, KSYN_QUEUE_WRITER, mgen, ins_flags, 0, psynch_mtxcontinue, kThreadWaitPThreadMutex);
        // ksyn_wait drops wait queue lock
out:
        ksyn_wqrelease(kwq, 1, (KSYN_WQTYPE_INWAIT|KSYN_WQTYPE_MTX));
        return error;
}

void
psynch_mtxcontinue(void *parameter, wait_result_t result)
{
        uthread_t uth = current_uthread();
        ksyn_wait_queue_t kwq = parameter;
        ksyn_waitq_element_t kwe = pthread_kern->uthread_get_uukwe(uth);
        
        int error = _wait_result_to_errno(result);
        if (error != 0) {
                ksyn_wqlock(kwq);
                if (kwe->kwe_kwqqueue) {
                        ksyn_queue_remove_item(kwq, &kwq->kw_ksynqueues[KSYN_QUEUE_WRITER], kwe);
                }
                ksyn_wqunlock(kwq);
        } else {
                uint32_t updatebits = kwe->kwe_psynchretval & ~PTH_RWL_MTX_WAIT;
                pthread_kern->uthread_set_returnval(uth, updatebits);
                
                if (updatebits == 0)
                        __FAILEDUSERTEST__("psynch_mutexwait: returning 0 lseq in mutexwait with no EBIT \n");
        }
        ksyn_wqrelease(kwq, 1, (KSYN_WQTYPE_INWAIT|KSYN_WQTYPE_MTX));
        pthread_kern->unix_syscall_return(error);
}

/*
 * psynch_mutexdrop: This system call is used for unlock postings on contended psynch mutexes.
 */
int
_psynch_mutexdrop(__unused proc_t p,
                  user_addr_t mutex,
                  uint32_t mgen,
                  uint32_t ugen,
                  uint64_t tid __unused,
                  uint32_t flags,
                  uint32_t *retval)
{
        int res;
        ksyn_wait_queue_t kwq;
        
        res = ksyn_wqfind(mutex, mgen, ugen, 0, flags, KSYN_WQTYPE_MUTEXDROP, &kwq);
        if (res == 0) {
                uint32_t updateval = _psynch_mutexdrop_internal(kwq, mgen, ugen, flags);
                /* drops the kwq reference */
                if (retval) {
                        *retval = updateval;
                }
        }

        return res;
}

static kern_return_t
ksyn_mtxsignal(ksyn_wait_queue_t kwq, ksyn_waitq_element_t kwe, uint32_t updateval)
{
        kern_return_t ret;
        boolean_t needs_commit;
        uint64_t kw_owner;

        if (!kwe) {
                kwe = TAILQ_FIRST(&kwq->kw_ksynqueues[KSYN_QUEUE_WRITER].ksynq_kwelist);
                if (!kwe) {
                        panic("ksyn_mtxsignal: panic signaling empty queue");
                }
        }

        needs_commit = ksyn_mtx_transfer_qos_override_begin(kwq, kwe, &kw_owner);
        kwq->kw_owner = kwe->kwe_tid;

        ret = ksyn_signal(kwq, KSYN_QUEUE_WRITER, kwe, updateval);

        // if waking the new owner failed, remove any overrides
        if (ret != KERN_SUCCESS) {
                ksyn_mtx_drop_qos_override(kwq);
                kwq->kw_owner = 0;
        } else if (needs_commit) {
                ksyn_mtx_transfer_qos_override_commit(kwq, kw_owner);
        }
        return ret;
}


static void
ksyn_prepost(ksyn_wait_queue_t kwq,
             ksyn_waitq_element_t kwe,
             uint32_t state,
             uint32_t lockseq)
{
        bzero(kwe, sizeof(*kwe));
        kwe->kwe_state = state;
        kwe->kwe_lockseq = lockseq;
        kwe->kwe_count = 1;
        
        (void)ksyn_queue_insert(kwq, KSYN_QUEUE_WRITER, kwe, lockseq, SEQFIT);
        kwq->kw_fakecount++;
}

static void
ksyn_cvsignal(ksyn_wait_queue_t ckwq,
              thread_t th,
              uint32_t uptoseq,
              uint32_t signalseq,
              uint32_t *updatebits,
              int *broadcast,
              ksyn_waitq_element_t *nkwep)
{
        ksyn_waitq_element_t kwe = NULL;
        ksyn_waitq_element_t nkwe = NULL;
        ksyn_queue_t kq = &ckwq->kw_ksynqueues[KSYN_QUEUE_WRITER];
        
        uptoseq &= PTHRW_COUNT_MASK;
        
        // Find the specified thread to wake.
        if (th != THREAD_NULL) {
                uthread_t uth = pthread_kern->get_bsdthread_info(th);
                kwe = pthread_kern->uthread_get_uukwe(uth);
                if (kwe->kwe_kwqqueue != ckwq ||
                    is_seqhigher(kwe->kwe_lockseq, uptoseq)) {
                        // Unless it's no longer waiting on this CV...
                        kwe = NULL;
                        // ...in which case we post a broadcast instead.
                        *broadcast = 1;
                        return;
                }
        }
        
        // If no thread was specified, find any thread to wake (with the right
        // sequence number).
        while (th == THREAD_NULL) {
                if (kwe == NULL) {
                        kwe = ksyn_queue_find_signalseq(ckwq, kq, uptoseq, signalseq);
                }
                if (kwe == NULL && nkwe == NULL) {
                        // No eligible entries; need to allocate a new
                        // entry to prepost. Loop to rescan after
                        // reacquiring the lock after allocation in
                        // case anything new shows up.
                        ksyn_wqunlock(ckwq);
                        nkwe = (ksyn_waitq_element_t)pthread_kern->zalloc(kwe_zone);
                        ksyn_wqlock(ckwq);
                } else {
                        break;
                }
        }
        
        if (kwe != NULL) {
                // If we found a thread to wake...
                if (kwe->kwe_state == KWE_THREAD_INWAIT) {
                        if (is_seqlower(kwe->kwe_lockseq, signalseq)) {
                                /*
                                 * A valid thread in our range, but lower than our signal.
                                 * Matching it may leave our match with nobody to wake it if/when
                                 * it arrives (the signal originally meant for this thread might
                                 * not successfully wake it).
                                 *
                                 * Convert to broadcast - may cause some spurious wakeups
                                 * (allowed by spec), but avoids starvation (better choice).
                                 */
                                *broadcast = 1;
                        } else {
                                (void)ksyn_signal(ckwq, KSYN_QUEUE_WRITER, kwe, PTH_RWL_MTX_WAIT);
                                *updatebits += PTHRW_INC;
                        }
                } else if (kwe->kwe_state == KWE_THREAD_PREPOST) {
                        // Merge with existing prepost at same uptoseq.
                        kwe->kwe_count += 1;
                } else if (kwe->kwe_state == KWE_THREAD_BROADCAST) {
                        // Existing broadcasts subsume this signal.
                } else {
                        panic("unknown kwe state\n");
                }
                if (nkwe) {
                        /*
                         * If we allocated a new kwe above but then found a different kwe to
                         * use then we need to deallocate the spare one.
                         */
                        pthread_kern->zfree(kwe_zone, nkwe);
                        nkwe = NULL;
                }
        } else if (nkwe != NULL) {
                // ... otherwise, insert the newly allocated prepost.
                ksyn_prepost(ckwq, nkwe, KWE_THREAD_PREPOST, uptoseq);
                nkwe = NULL;
        } else {
                panic("failed to allocate kwe\n");
        }
        
        *nkwep = nkwe;
}

static int
__psynch_cvsignal(user_addr_t cv,
                  uint32_t cgen,
                  uint32_t cugen,
                  uint32_t csgen,
                  uint32_t flags,
                  int broadcast,
                  mach_port_name_t threadport,
                  uint32_t *retval)
{
        int error = 0;
        thread_t th = THREAD_NULL;
        ksyn_wait_queue_t kwq;
        
        uint32_t uptoseq = cgen & PTHRW_COUNT_MASK;
        uint32_t fromseq = (cugen & PTHRW_COUNT_MASK) + PTHRW_INC;
        
        // validate sane L, U, and S values
        if ((threadport == 0 && is_seqhigher(fromseq, uptoseq)) || is_seqhigher(csgen, uptoseq)) {
                __FAILEDUSERTEST__("cvbroad: invalid L, U and S values\n");
                return EINVAL;
        }
        
        if (threadport != 0) {
                th = port_name_to_thread((mach_port_name_t)threadport);
                if (th == THREAD_NULL) {
                        return ESRCH;
                }
        }
        
        error = ksyn_wqfind(cv, cgen, cugen, csgen, flags, (KSYN_WQTYPE_CVAR | KSYN_WQTYPE_INDROP), &kwq);
        if (error == 0) {
                uint32_t updatebits = 0;
                ksyn_waitq_element_t nkwe = NULL;
                
                ksyn_wqlock(kwq);
                
                // update L, U and S...
                UPDATE_CVKWQ(kwq, cgen, cugen, csgen);
                
                if (!broadcast) {
                        // No need to signal if the CV is already balanced.
                        if (diff_genseq(kwq->kw_lword, kwq->kw_sword)) {
                                ksyn_cvsignal(kwq, th, uptoseq, fromseq, &updatebits, &broadcast, &nkwe);
                        }
                }
                
                if (broadcast) {
                        ksyn_handle_cvbroad(kwq, uptoseq, &updatebits);
                }
                
                kwq->kw_sword += (updatebits & PTHRW_COUNT_MASK);
                // set C or P bits and free if needed
                ksyn_cvupdate_fixup(kwq, &updatebits);
                *retval = updatebits;
                
                ksyn_wqunlock(kwq);
                
                if (nkwe != NULL) {
                        pthread_kern->zfree(kwe_zone, nkwe);
                }
                
                ksyn_wqrelease(kwq, 1, (KSYN_WQTYPE_INDROP | KSYN_WQTYPE_CVAR));
        }
        
        if (th != NULL) {
                thread_deallocate(th);
        }
        
        return error;
}

/*
 * psynch_cvbroad: This system call is used for broadcast posting on blocked waiters of psynch cvars.
 */
int
_psynch_cvbroad(__unused proc_t p,
                user_addr_t cv,
                uint64_t cvlsgen,
                uint64_t cvudgen,
                uint32_t flags,
                __unused user_addr_t mutex,
                __unused uint64_t mugen,
                __unused uint64_t tid,
                uint32_t *retval)
{
        uint32_t diffgen = cvudgen & 0xffffffff;
        uint32_t count = diffgen >> PTHRW_COUNT_SHIFT;
        if (count > pthread_kern->get_task_threadmax()) {
                __FAILEDUSERTEST__("cvbroad: difference greater than maximum possible thread count\n");
                return EBUSY;
        }
        
        uint32_t csgen = (cvlsgen >> 32) & 0xffffffff;
        uint32_t cgen = cvlsgen & 0xffffffff;
        uint32_t cugen = (cvudgen >> 32) & 0xffffffff;
        
        return __psynch_cvsignal(cv, cgen, cugen, csgen, flags, 1, 0, retval);
}

/*
 * psynch_cvsignal: This system call is used for signalling the blocked waiters of psynch cvars.
 */
int
_psynch_cvsignal(__unused proc_t p,
                 user_addr_t cv,
                 uint64_t cvlsgen,
                 uint32_t cvugen,
                 int threadport,
                 __unused user_addr_t mutex,
                 __unused uint64_t mugen,
                 __unused uint64_t tid,
                 uint32_t flags,
                 uint32_t *retval)
{
        uint32_t csgen = (cvlsgen >> 32) & 0xffffffff;
        uint32_t cgen = cvlsgen & 0xffffffff;
        
        return __psynch_cvsignal(cv, cgen, cvugen, csgen, flags, 0, threadport, retval);
}

/*
 * psynch_cvwait: This system call is used for psynch cvar waiters to block in kernel.
 */
int
_psynch_cvwait(__unused proc_t p,
               user_addr_t cv,
               uint64_t cvlsgen,
               uint32_t cvugen,
               user_addr_t mutex,
               uint64_t mugen,
               uint32_t flags,
               int64_t sec,
               uint32_t nsec,
               uint32_t *retval)
{
        int error = 0;
        uint32_t updatebits = 0;
        ksyn_wait_queue_t ckwq = NULL;
        ksyn_waitq_element_t kwe, nkwe = NULL;
        
        /* for conformance reasons */
        pthread_kern->__pthread_testcancel(0);
        
        uint32_t csgen = (cvlsgen >> 32) & 0xffffffff;
        uint32_t cgen = cvlsgen & 0xffffffff;
        uint32_t ugen = (mugen >> 32) & 0xffffffff;
        uint32_t mgen = mugen & 0xffffffff;
        
        uint32_t lockseq = (cgen & PTHRW_COUNT_MASK);
        
        /*
         * In cvwait U word can be out of range as cv could be used only for
         * timeouts. However S word needs to be within bounds and validated at
         * user level as well.
         */
        if (is_seqhigher_eq(csgen, lockseq) != 0) {
                __FAILEDUSERTEST__("psync_cvwait; invalid sequence numbers\n");
                return EINVAL;
        }
        
        error = ksyn_wqfind(cv, cgen, cvugen, csgen, flags, KSYN_WQTYPE_CVAR | KSYN_WQTYPE_INWAIT, &ckwq);
        if (error != 0) {
                return error;
        }
        
        if (mutex != 0) {
                error = _psynch_mutexdrop(NULL, mutex, mgen, ugen, 0, flags, NULL);
                if (error != 0) {
                        goto out;
                }
        }
        
        ksyn_wqlock(ckwq);
        
        // update L, U and S...
        UPDATE_CVKWQ(ckwq, cgen, cvugen, csgen);
        
        /* Look for the sequence for prepost (or conflicting thread */
        ksyn_queue_t kq = &ckwq->kw_ksynqueues[KSYN_QUEUE_WRITER];
        kwe = ksyn_queue_find_cvpreposeq(kq, lockseq);
        if (kwe != NULL) {
                if (kwe->kwe_state == KWE_THREAD_PREPOST) {
                        if ((kwe->kwe_lockseq & PTHRW_COUNT_MASK) == lockseq) {
                                /* we can safely consume a reference, so do so */
                                if (--kwe->kwe_count == 0) {
                                        ksyn_queue_remove_item(ckwq, kq, kwe);
                                        ckwq->kw_fakecount--;
                                        nkwe = kwe;
                                }
                        } else {
                                /*
                                 * consuming a prepost higher than our lock sequence is valid, but
                                 * can leave the higher thread without a match. Convert the entry
                                 * to a broadcast to compensate for this.
                                 */
                                ksyn_handle_cvbroad(ckwq, kwe->kwe_lockseq, &updatebits);
#if __TESTPANICS__
                                if (updatebits != 0)
                                        panic("psync_cvwait: convert pre-post to broadcast: woke up %d threads that shouldn't be there\n", updatebits);
#endif /* __TESTPANICS__ */
                        }
                } else if (kwe->kwe_state == KWE_THREAD_BROADCAST) {
                        // XXX
                        // Nothing to do.
                } else if (kwe->kwe_state == KWE_THREAD_INWAIT) {
                        __FAILEDUSERTEST__("cvwait: thread entry with same sequence already present\n");
                        error = EBUSY;
                } else {
                        panic("psync_cvwait: unexpected wait queue element type\n");
                }
                
                if (error == 0) {
                        updatebits = PTHRW_INC;
                        ckwq->kw_sword += PTHRW_INC;
                        
                        /* set C or P bits and free if needed */
                        ksyn_cvupdate_fixup(ckwq, &updatebits);
                        *retval = updatebits;
                }
        } else {
                uint64_t abstime = 0;

                if (sec != 0 || (nsec & 0x3fffffff) != 0) {
                        struct timespec ts;
                        ts.tv_sec = (__darwin_time_t)sec;
                        ts.tv_nsec = (nsec & 0x3fffffff);
                        nanoseconds_to_absolutetime((uint64_t)ts.tv_sec * NSEC_PER_SEC + ts.tv_nsec, &abstime);
                        clock_absolutetime_interval_to_deadline(abstime, &abstime);
                }
                
                error = ksyn_wait(ckwq, KSYN_QUEUE_WRITER, cgen, SEQFIT, abstime, psynch_cvcontinue, kThreadWaitPThreadCondVar);
                // ksyn_wait drops wait queue lock
        }
        
        ksyn_wqunlock(ckwq);
        
        if (nkwe != NULL) {
                pthread_kern->zfree(kwe_zone, nkwe);
        }
out:
        ksyn_wqrelease(ckwq, 1, (KSYN_WQTYPE_INWAIT | KSYN_WQTYPE_CVAR));
        return error;
}


void
psynch_cvcontinue(void *parameter, wait_result_t result)
{
        uthread_t uth = current_uthread();
        ksyn_wait_queue_t ckwq = parameter;
        ksyn_waitq_element_t kwe = pthread_kern->uthread_get_uukwe(uth);
        
        int error = _wait_result_to_errno(result);
        if (error != 0) {
                ksyn_wqlock(ckwq);
                /* just in case it got woken up as we were granting */
                pthread_kern->uthread_set_returnval(uth, kwe->kwe_psynchretval);

                if (kwe->kwe_kwqqueue) {
                        ksyn_queue_remove_item(ckwq, &ckwq->kw_ksynqueues[KSYN_QUEUE_WRITER], kwe);
                }
                if ((kwe->kwe_psynchretval & PTH_RWL_MTX_WAIT) != 0) {
                        /* the condition var granted.
                         * reset the error so that the thread returns back.
                         */
                        error = 0;
                        /* no need to set any bits just return as cvsig/broad covers this */
                } else {
                        ckwq->kw_sword += PTHRW_INC;
                        
                        /* set C and P bits, in the local error */
                        if ((ckwq->kw_lword & PTHRW_COUNT_MASK) == (ckwq->kw_sword & PTHRW_COUNT_MASK)) {
                                error |= ECVCERORR;
                                if (ckwq->kw_inqueue != 0) {
                                        ksyn_queue_free_items(ckwq, KSYN_QUEUE_WRITER, ckwq->kw_lword, 1);
                                }
                                ckwq->kw_lword = ckwq->kw_uword = ckwq->kw_sword = 0;
                                ckwq->kw_kflags |= KSYN_KWF_ZEROEDOUT;
                        } else {
                                /* everythig in the queue is a fake entry ? */
                                if (ckwq->kw_inqueue != 0 && ckwq->kw_fakecount == ckwq->kw_inqueue) {
                                        error |= ECVPERORR;
                                }
                        }
                }
                ksyn_wqunlock(ckwq);
        } else {
                int val = 0;
                // PTH_RWL_MTX_WAIT is removed
                if ((kwe->kwe_psynchretval & PTH_RWS_CV_MBIT) != 0) {
                        val = PTHRW_INC | PTH_RWS_CV_CBIT;
                }
                pthread_kern->uthread_set_returnval(uth, val);
        }
        
        ksyn_wqrelease(ckwq, 1, (KSYN_WQTYPE_INWAIT | KSYN_WQTYPE_CVAR));
        pthread_kern->unix_syscall_return(error);
}

/*
 * psynch_cvclrprepost: This system call clears pending prepost if present.
 */
int
_psynch_cvclrprepost(__unused proc_t p,
                     user_addr_t cv,
                     uint32_t cvgen,
                     uint32_t cvugen,
                     uint32_t cvsgen,
                     __unused uint32_t prepocnt,
                     uint32_t preposeq,
                     uint32_t flags,
                     int *retval)
{
        int error = 0;
        int mutex = (flags & _PTHREAD_MTX_OPT_MUTEX);
        int wqtype = (mutex ? KSYN_WQTYPE_MTX : KSYN_WQTYPE_CVAR) | KSYN_WQTYPE_INDROP;
        ksyn_wait_queue_t kwq = NULL;
        
        *retval = 0;
        
        error = ksyn_wqfind(cv, cvgen, cvugen, mutex ? 0 : cvsgen, flags, wqtype, &kwq);
        if (error != 0) {
                return error;
        }
        
        ksyn_wqlock(kwq);
        
        if (mutex) {
                int firstfit = (flags & PTHREAD_POLICY_FLAGS_MASK) == _PTHREAD_MUTEX_POLICY_FIRSTFIT;
                if (firstfit && kwq->kw_pre_rwwc != 0) {
                        if (is_seqlower_eq(kwq->kw_pre_lockseq, cvgen)) {
                                // clear prepost
                                kwq->kw_pre_rwwc = 0;
                                kwq->kw_pre_lockseq = 0;
                        }
                }
        } else {
                ksyn_queue_free_items(kwq, KSYN_QUEUE_WRITER, preposeq, 0);
        }
        
        ksyn_wqunlock(kwq);
        ksyn_wqrelease(kwq, 1, wqtype);
        return error;
}

/* ***************** pthread_rwlock ************************ */

static int
__psynch_rw_lock(int type,
                 user_addr_t rwlock,
                 uint32_t lgenval,
                 uint32_t ugenval,
                 uint32_t rw_wc,
                 int flags,
                 uint32_t *retval)
{
        int prepost_type, kqi;

        if (type == PTH_RW_TYPE_READ) {
                prepost_type = KW_UNLOCK_PREPOST_READLOCK;
                kqi = KSYN_QUEUE_READ;
        } else {
                prepost_type = KW_UNLOCK_PREPOST_WRLOCK;
                kqi = KSYN_QUEUE_WRITER;
        }

        uint32_t lockseq = lgenval & PTHRW_COUNT_MASK;

        int error;
        ksyn_wait_queue_t kwq;
        error = ksyn_wqfind(rwlock, lgenval, ugenval, rw_wc, flags, (KSYN_WQTYPE_INWAIT|KSYN_WQTYPE_RWLOCK), &kwq);
        if (error == 0) {
                ksyn_wqlock(kwq);
                _ksyn_check_init(kwq, lgenval);
                if (_ksyn_handle_missed_wakeups(kwq, type, lockseq, retval) ||
                    // handle overlap first as they are not counted against pre_rwwc
                    (type == PTH_RW_TYPE_READ && _ksyn_handle_overlap(kwq, lgenval, rw_wc, retval)) ||
                    _ksyn_handle_prepost(kwq, prepost_type, lockseq, retval)) {
                        ksyn_wqunlock(kwq);
                } else {
                        block_hint_t block_hint = type == PTH_RW_TYPE_READ ?
                                kThreadWaitPThreadRWLockRead : kThreadWaitPThreadRWLockWrite;
                        error = ksyn_wait(kwq, kqi, lgenval, SEQFIT, 0, THREAD_CONTINUE_NULL, block_hint);
                        // ksyn_wait drops wait queue lock
                        if (error == 0) {
                                uthread_t uth = current_uthread();
                                ksyn_waitq_element_t kwe = pthread_kern->uthread_get_uukwe(uth);
                                *retval = kwe->kwe_psynchretval;
                        }
                }
                ksyn_wqrelease(kwq, 0, (KSYN_WQTYPE_INWAIT|KSYN_WQTYPE_RWLOCK));
        }
        return error;
}

/*
 * psynch_rw_rdlock: This system call is used for psync rwlock readers to block.
 */
int
_psynch_rw_rdlock(__unused proc_t p,
                  user_addr_t rwlock,
                  uint32_t lgenval,
                  uint32_t ugenval,
                  uint32_t rw_wc,
                  int flags,
                  uint32_t *retval)
{
        return __psynch_rw_lock(PTH_RW_TYPE_READ, rwlock, lgenval, ugenval, rw_wc, flags, retval);
}

/*
 * psynch_rw_longrdlock: This system call is used for psync rwlock long readers to block.
 */
int
_psynch_rw_longrdlock(__unused proc_t p,
                      __unused user_addr_t rwlock,
                      __unused uint32_t lgenval,
                      __unused uint32_t ugenval,
                      __unused uint32_t rw_wc,
                      __unused int flags,
                      __unused uint32_t *retval)
{
        return ESRCH;
}


/*
 * psynch_rw_wrlock: This system call is used for psync rwlock writers to block.
 */
int
_psynch_rw_wrlock(__unused proc_t p,
                  user_addr_t rwlock,
                  uint32_t lgenval,
                  uint32_t ugenval,
                  uint32_t rw_wc,
                  int flags,
                  uint32_t *retval)
{
        return __psynch_rw_lock(PTH_RW_TYPE_WRITE, rwlock, lgenval, ugenval, rw_wc, flags, retval);
}

/*
 * psynch_rw_yieldwrlock: This system call is used for psync rwlock yielding writers to block.
 */
int
_psynch_rw_yieldwrlock(__unused proc_t p,
                       __unused user_addr_t rwlock,
                       __unused uint32_t lgenval,
                       __unused uint32_t ugenval,
                       __unused uint32_t rw_wc,
                       __unused int flags,
                       __unused uint32_t *retval)
{
        return ESRCH;
}

/*
 * psynch_rw_unlock: This system call is used for unlock state postings. This will grant appropriate
 *                      reader/writer variety lock.
 */
int
_psynch_rw_unlock(__unused proc_t p,
                  user_addr_t rwlock,
                  uint32_t lgenval,
                  uint32_t ugenval,
                  uint32_t rw_wc,
                  int flags,
                  uint32_t *retval)
{
        int error = 0;
        ksyn_wait_queue_t kwq;
        uint32_t updatebits = 0;
        int diff;
        uint32_t count = 0;
        uint32_t curgen = lgenval & PTHRW_COUNT_MASK;
        int clearedkflags = 0;

        error = ksyn_wqfind(rwlock, lgenval, ugenval, rw_wc, flags, (KSYN_WQTYPE_INDROP | KSYN_WQTYPE_RWLOCK), &kwq);
        if (error != 0) {
                return(error);
        }
        
        ksyn_wqlock(kwq);
        int isinit = _ksyn_check_init(kwq, lgenval);

        /* if lastunlock seq is set, ensure the current one is not lower than that, as it would be spurious */
        if ((kwq->kw_lastunlockseq != PTHRW_RWL_INIT) && (is_seqlower(ugenval, kwq->kw_lastunlockseq)!= 0)) {
                error = 0;
                goto out;
        }
        
        /* If L-U != num of waiters, then it needs to be preposted or spr */
        diff = find_diff(lgenval, ugenval);
        
        if (find_seq_till(kwq, curgen, diff, &count) == 0) {
                if ((count == 0) || (count < (uint32_t)diff))
                        goto prepost;
        }
        
        /* no prepost and all threads are in place, reset the bit */
        if ((isinit != 0) && ((kwq->kw_kflags & KSYN_KWF_INITCLEARED) != 0)){
                kwq->kw_kflags &= ~KSYN_KWF_INITCLEARED;
                clearedkflags = 1;
        }
        
        /* can handle unlock now */
        
        CLEAR_PREPOST_BITS(kwq);
        
        error = kwq_handle_unlock(kwq, lgenval, rw_wc, &updatebits, 0, NULL, 0);
#if __TESTPANICS__
        if (error != 0)
                panic("psynch_rw_unlock: kwq_handle_unlock failed %d\n",error);
#endif /* __TESTPANICS__ */
out:
        if (error == 0) {
                /* update bits?? */
                *retval = updatebits;
        }

        // <rdar://problem/22244050> If any of the wakeups failed because they already
        // returned to userspace because of a signal then we need to ensure that the
        // reset state is not cleared when that thread returns. Otherwise,
        // _pthread_rwlock_lock will clear the interrupted state before it is read.
        if (clearedkflags != 0 && kwq->kw_pre_intrcount > 0) {
                kwq->kw_kflags |= KSYN_KWF_INITCLEARED;
        }
        
        ksyn_wqunlock(kwq);
        ksyn_wqrelease(kwq, 0, (KSYN_WQTYPE_INDROP | KSYN_WQTYPE_RWLOCK));
        
        return(error);
        
prepost:
        /* update if the new seq is higher than prev prepost, or first set */
        if (is_rws_setseq(kwq->kw_pre_sseq) ||
            is_seqhigher_eq(rw_wc, kwq->kw_pre_sseq)) {
                kwq->kw_pre_rwwc = (diff - count);
                kwq->kw_pre_lockseq = curgen;
                kwq->kw_pre_sseq = rw_wc;
                updatebits = lgenval;   /* let this not do unlock handling */
        }
        error = 0;
        goto out;
}


/* ************************************************************************** */
void
pth_global_hashinit(void)
{
        pth_glob_hashtbl = hashinit(PTH_HASHSIZE * 4, M_PROC, &pthhash);
}

void
_pth_proc_hashinit(proc_t p)
{
        void *ptr = hashinit(PTH_HASHSIZE, M_PCB, &pthhash);
        if (ptr == NULL) {
                panic("pth_proc_hashinit: hash init returned 0\n");
        }
        
        pthread_kern->proc_set_pthhash(p, ptr);
}


static int
ksyn_wq_hash_lookup(user_addr_t uaddr,
                    proc_t p,
                    int flags,
                    ksyn_wait_queue_t *out_kwq,
                    struct pthhashhead **out_hashptr,
                    uint64_t *out_object,
                    uint64_t *out_offset)
{
        int res = 0;
        ksyn_wait_queue_t kwq;
        uint64_t object = 0, offset = 0;
        struct pthhashhead *hashptr;
        if ((flags & PTHREAD_PSHARED_FLAGS_MASK) == PTHREAD_PROCESS_SHARED) {
                hashptr = pth_glob_hashtbl;
                res = ksyn_findobj(uaddr, &object, &offset);
                if (res == 0) {
                        LIST_FOREACH(kwq, &hashptr[object & pthhash], kw_hash) {
                                if (kwq->kw_object == object && kwq->kw_offset == offset) {
                                        break;
                                }
                        }
                } else {
                        kwq = NULL;
                }
        } else {
                hashptr = pthread_kern->proc_get_pthhash(p);
                LIST_FOREACH(kwq, &hashptr[uaddr & pthhash], kw_hash) {
                        if (kwq->kw_addr == uaddr) {
                                break;
                        }
                }
        }
        *out_kwq = kwq;
        *out_object = object;
        *out_offset = offset;
        *out_hashptr = hashptr;
        return res;
}

void
_pth_proc_hashdelete(proc_t p)
{
        struct pthhashhead * hashptr;
        ksyn_wait_queue_t kwq;
        unsigned long hashsize = pthhash + 1;
        unsigned long i;
        
        hashptr = pthread_kern->proc_get_pthhash(p);
        pthread_kern->proc_set_pthhash(p, NULL);
        if (hashptr == NULL) {
                return;
        }
        
        pthread_list_lock();
        for(i= 0; i < hashsize; i++) {
                while ((kwq = LIST_FIRST(&hashptr[i])) != NULL) {
                        if ((kwq->kw_pflags & KSYN_WQ_INHASH) != 0) {
                                kwq->kw_pflags &= ~KSYN_WQ_INHASH;
                                LIST_REMOVE(kwq, kw_hash);
                        }
                        if ((kwq->kw_pflags & KSYN_WQ_FLIST) != 0) {
                                kwq->kw_pflags &= ~KSYN_WQ_FLIST;
                                LIST_REMOVE(kwq, kw_list);
                        }
                        pthread_list_unlock();
                        /* release fake entries if present for cvars */
                        if (((kwq->kw_type & KSYN_WQTYPE_MASK) == KSYN_WQTYPE_CVAR) && (kwq->kw_inqueue != 0))
                                ksyn_freeallkwe(&kwq->kw_ksynqueues[KSYN_QUEUE_WRITER]);
                        lck_mtx_destroy(&kwq->kw_lock, pthread_lck_grp);
                        pthread_kern->zfree(kwq_zone, kwq);
                        pthread_list_lock();
                }
        }
        pthread_list_unlock();
        FREE(hashptr, M_PROC);
}

/* no lock held for this as the waitqueue is getting freed */
void
ksyn_freeallkwe(ksyn_queue_t kq)
{
        ksyn_waitq_element_t kwe;
        while ((kwe = TAILQ_FIRST(&kq->ksynq_kwelist)) != NULL) {
                TAILQ_REMOVE(&kq->ksynq_kwelist, kwe, kwe_list);
                if (kwe->kwe_state != KWE_THREAD_INWAIT) {
                        pthread_kern->zfree(kwe_zone, kwe);
                }
        }
}

/* find kernel waitqueue, if not present create one. Grants a reference  */
int
ksyn_wqfind(user_addr_t uaddr, uint32_t mgen, uint32_t ugen, uint32_t sgen, int flags, int wqtype, ksyn_wait_queue_t *kwqp)
{
        int res = 0;
        ksyn_wait_queue_t kwq = NULL;
        ksyn_wait_queue_t nkwq = NULL;
        struct pthhashhead *hashptr;
        proc_t p = current_proc();
        
        uint64_t object = 0, offset = 0;
        if ((flags & PTHREAD_PSHARED_FLAGS_MASK) == PTHREAD_PROCESS_SHARED) {
                res = ksyn_findobj(uaddr, &object, &offset);
                hashptr = pth_glob_hashtbl;
        } else {
                hashptr = pthread_kern->proc_get_pthhash(p);
        }

        while (res == 0) {
                pthread_list_lock();
                res = ksyn_wq_hash_lookup(uaddr, current_proc(), flags, &kwq, &hashptr, &object, &offset);
                if (res != 0) {
                        pthread_list_unlock();
                        break;
                }
                if (kwq == NULL && nkwq == NULL) {
                        // Drop the lock to allocate a new kwq and retry.
                        pthread_list_unlock();

                        nkwq = (ksyn_wait_queue_t)pthread_kern->zalloc(kwq_zone);
                        bzero(nkwq, sizeof(struct ksyn_wait_queue));
                        int i;
                        for (i = 0; i < KSYN_QUEUE_MAX; i++) {
                                ksyn_queue_init(&nkwq->kw_ksynqueues[i]);
                        }
                        lck_mtx_init(&nkwq->kw_lock, pthread_lck_grp, pthread_lck_attr);
                        continue;
                } else if (kwq == NULL && nkwq != NULL) {
                        // Still not found, add the new kwq to the hash.
                        kwq = nkwq;
                        nkwq = NULL; // Don't free.
                        if ((flags & PTHREAD_PSHARED_FLAGS_MASK) == PTHREAD_PROCESS_SHARED) {
                                kwq->kw_pflags |= KSYN_WQ_SHARED;
                                LIST_INSERT_HEAD(&hashptr[object & pthhash], kwq, kw_hash);
                        } else {
                                LIST_INSERT_HEAD(&hashptr[uaddr & pthhash], kwq, kw_hash);
                        }
                        kwq->kw_pflags |= KSYN_WQ_INHASH;
                } else if (kwq != NULL) {
                        // Found an existing kwq, use it.
                        if ((kwq->kw_pflags & KSYN_WQ_FLIST) != 0) {
                                LIST_REMOVE(kwq, kw_list);
                                kwq->kw_pflags &= ~KSYN_WQ_FLIST;
                        }
                        if ((kwq->kw_type & KSYN_WQTYPE_MASK) != (wqtype & KSYN_WQTYPE_MASK)) {
                                if (kwq->kw_inqueue == 0 && kwq->kw_pre_rwwc == 0 && kwq->kw_pre_intrcount == 0) {
                                        if (kwq->kw_iocount == 0) {
                                                kwq->kw_type = 0; // mark for reinitialization
                                        } else if (kwq->kw_iocount == 1 && kwq->kw_dropcount == kwq->kw_iocount) {
                                                /* if all users are unlockers then wait for it to finish */
                                                kwq->kw_pflags |= KSYN_WQ_WAITING;
                                                // Drop the lock and wait for the kwq to be free.
                                                (void)msleep(&kwq->kw_pflags, pthread_list_mlock, PDROP, "ksyn_wqfind", 0);
                                                continue;
                                        } else {
                                                __FAILEDUSERTEST__("address already known to kernel for another [busy] synchronizer type\n");
                                                res = EINVAL;
                                        }
                                } else {
                                        __FAILEDUSERTEST__("address already known to kernel for another [busy] synchronizer type\n");
                                        res = EINVAL;
                                }
                        }
                }
                if (res == 0) {
                        if (kwq->kw_type == 0) {
                                kwq->kw_addr = uaddr;
                                kwq->kw_object = object;
                                kwq->kw_offset = offset;
                                kwq->kw_type = (wqtype & KSYN_WQTYPE_MASK);
                                CLEAR_REINIT_BITS(kwq);
                                kwq->kw_lword = mgen;
                                kwq->kw_uword = ugen;
                                kwq->kw_sword = sgen;
                                kwq->kw_owner = 0;
                                kwq->kw_kflags = 0;
                                kwq->kw_qos_override = THREAD_QOS_UNSPECIFIED;
                        }
                        kwq->kw_iocount++;
                        if (wqtype == KSYN_WQTYPE_MUTEXDROP) {
                                kwq->kw_dropcount++;
                        }
                }
                pthread_list_unlock();
                break;
        }
        if (kwqp != NULL) {
                *kwqp = kwq;
        }
        if (nkwq) {
                lck_mtx_destroy(&nkwq->kw_lock, pthread_lck_grp);
                pthread_kern->zfree(kwq_zone, nkwq);
        }
        return res;
}

/* Reference from find is dropped here. Starts the free process if needed */
void
ksyn_wqrelease(ksyn_wait_queue_t kwq, int qfreenow, int wqtype)
{
        uint64_t deadline;
        ksyn_wait_queue_t free_elem = NULL;
        
        pthread_list_lock();
        if (wqtype == KSYN_WQTYPE_MUTEXDROP) {
                kwq->kw_dropcount--;
        }
        if (--kwq->kw_iocount == 0) {
                if ((kwq->kw_pflags & KSYN_WQ_WAITING) != 0) {
                        /* some one is waiting for the waitqueue, wake them up */
                        kwq->kw_pflags &= ~KSYN_WQ_WAITING;
                        wakeup(&kwq->kw_pflags);
                }
                
                if (kwq->kw_pre_rwwc == 0 && kwq->kw_inqueue == 0 && kwq->kw_pre_intrcount == 0) {
                        if (qfreenow == 0) {
                                microuptime(&kwq->kw_ts);
                                LIST_INSERT_HEAD(&pth_free_list, kwq, kw_list);
                                kwq->kw_pflags |= KSYN_WQ_FLIST;
                                if (psynch_cleanupset == 0) {
                                        struct timeval t;
                                        microuptime(&t);
                                        t.tv_sec += KSYN_CLEANUP_DEADLINE;
                                        deadline = tvtoabstime(&t);
                                        thread_call_enter_delayed(psynch_thcall, deadline);
                                        psynch_cleanupset = 1;
                                }
                        } else {
                                kwq->kw_pflags &= ~KSYN_WQ_INHASH;
                                LIST_REMOVE(kwq, kw_hash);
                                free_elem = kwq;
                        }
                }
        }
        pthread_list_unlock();
        if (free_elem != NULL) {
                lck_mtx_destroy(&free_elem->kw_lock, pthread_lck_grp);
                pthread_kern->zfree(kwq_zone, free_elem);
        }
}

/* responsible to free the waitqueues */
void
psynch_wq_cleanup(__unused void *param, __unused void * param1)
{
        ksyn_wait_queue_t kwq;
        struct timeval t;
        int reschedule = 0;
        uint64_t deadline = 0;
        LIST_HEAD(, ksyn_wait_queue) freelist;
        LIST_INIT(&freelist);

        pthread_list_lock();
        
        microuptime(&t);
        
        LIST_FOREACH(kwq, &pth_free_list, kw_list) {
                if (kwq->kw_iocount != 0 || kwq->kw_pre_rwwc != 0 || kwq->kw_inqueue != 0 || kwq->kw_pre_intrcount != 0) {
                        // still in use
                        continue;
                }
                __darwin_time_t diff = t.tv_sec - kwq->kw_ts.tv_sec;
                if (diff < 0)
                        diff *= -1;
                if (diff >= KSYN_CLEANUP_DEADLINE) {
                        kwq->kw_pflags &= ~(KSYN_WQ_FLIST | KSYN_WQ_INHASH);
                        LIST_REMOVE(kwq, kw_hash);
                        LIST_REMOVE(kwq, kw_list);
                        LIST_INSERT_HEAD(&freelist, kwq, kw_list);
                } else {
                        reschedule = 1;
                }
                
        }
        if (reschedule != 0) {
                t.tv_sec += KSYN_CLEANUP_DEADLINE;
                deadline = tvtoabstime(&t);
                thread_call_enter_delayed(psynch_thcall, deadline);
                psynch_cleanupset = 1;
        } else {
                psynch_cleanupset = 0;
        }
        pthread_list_unlock();

        while ((kwq = LIST_FIRST(&freelist)) != NULL) {
                LIST_REMOVE(kwq, kw_list);
                lck_mtx_destroy(&kwq->kw_lock, pthread_lck_grp);
                pthread_kern->zfree(kwq_zone, kwq);
        }
}

static int
_wait_result_to_errno(wait_result_t result)
{
        int res = 0;
        switch (result) {
                case THREAD_TIMED_OUT:
                        res = ETIMEDOUT;
                        break;
                case THREAD_INTERRUPTED:
                        res = EINTR;
                        break;
        }
        return res;
}

int
ksyn_wait(ksyn_wait_queue_t kwq,
          int kqi,
          uint32_t lockseq,
          int fit,
          uint64_t abstime,
          thread_continue_t continuation,
          block_hint_t block_hint)
{
        int res;

        thread_t th = current_thread();
        uthread_t uth = pthread_kern->get_bsdthread_info(th);
        ksyn_waitq_element_t kwe = pthread_kern->uthread_get_uukwe(uth);
        bzero(kwe, sizeof(*kwe));
        kwe->kwe_count = 1;
        kwe->kwe_lockseq = lockseq & PTHRW_COUNT_MASK;
        kwe->kwe_state = KWE_THREAD_INWAIT;
        kwe->kwe_uth = uth;
        kwe->kwe_tid = thread_tid(th);

        res = ksyn_queue_insert(kwq, kqi, kwe, lockseq, fit);
        if (res != 0) {
                //panic("psynch_rw_wrlock: failed to enqueue\n"); // XXX
                ksyn_wqunlock(kwq);
                return res;
        }
        
        thread_set_pending_block_hint(th, block_hint);
        assert_wait_deadline_with_leeway(&kwe->kwe_psynchretval, THREAD_ABORTSAFE, TIMEOUT_URGENCY_USER_NORMAL, abstime, 0);
        ksyn_wqunlock(kwq);
        
        kern_return_t ret;
        if (continuation == THREAD_CONTINUE_NULL) {
                ret = thread_block(NULL);
        } else {
                ret = thread_block_parameter(continuation, kwq);
                
                // If thread_block_parameter returns (interrupted) call the
                // continuation manually to clean up.
                continuation(kwq, ret);
                
                // NOT REACHED
                panic("ksyn_wait continuation returned");
        }
        
        res = _wait_result_to_errno(ret);
        if (res != 0) {
                ksyn_wqlock(kwq);
                if (kwe->kwe_kwqqueue) {
                        ksyn_queue_remove_item(kwq, &kwq->kw_ksynqueues[kqi], kwe);
                }
                ksyn_wqunlock(kwq);
        }
        return res;
}

kern_return_t
ksyn_signal(ksyn_wait_queue_t kwq,
            int kqi,
            ksyn_waitq_element_t kwe,
            uint32_t updateval)
{
        kern_return_t ret;

        // If no wait element was specified, wake the first.
        if (!kwe) {
                kwe = TAILQ_FIRST(&kwq->kw_ksynqueues[kqi].ksynq_kwelist);
                if (!kwe) {
                        panic("ksyn_signal: panic signaling empty queue");
                }
        }

        if (kwe->kwe_state != KWE_THREAD_INWAIT) {
                panic("ksyn_signal: panic signaling non-waiting element");
        }

        ksyn_queue_remove_item(kwq, &kwq->kw_ksynqueues[kqi], kwe);
        kwe->kwe_psynchretval = updateval;

        ret = thread_wakeup_one((caddr_t)&kwe->kwe_psynchretval);
        if (ret != KERN_SUCCESS && ret != KERN_NOT_WAITING) {
                panic("ksyn_signal: panic waking up thread %x\n", ret);
        }
        return ret;
}

int
ksyn_findobj(user_addr_t uaddr, uint64_t *objectp, uint64_t *offsetp)
{
        kern_return_t ret;
        vm_page_info_basic_data_t info;
        mach_msg_type_number_t count = VM_PAGE_INFO_BASIC_COUNT;
        ret = pthread_kern->vm_map_page_info(pthread_kern->current_map(), uaddr, VM_PAGE_INFO_BASIC, (vm_page_info_t)&info, &count);
        if (ret != KERN_SUCCESS) {
                return EINVAL;
        }
        
        if (objectp != NULL) {
                *objectp = (uint64_t)info.object_id;
        }
        if (offsetp != NULL) {
                *offsetp = (uint64_t)info.offset;
        }
        
        return(0);
}


/* lowest of kw_fr, kw_flr, kw_fwr, kw_fywr */
int
kwq_find_rw_lowest(ksyn_wait_queue_t kwq, int flags, uint32_t premgen, int *typep, uint32_t lowest[])
{
        uint32_t kw_fr, kw_fwr, low;
        int type = 0, lowtype, typenum[2] = { 0 };
        uint32_t numbers[2] = { 0 };
        int count = 0, i;
        
        
        if ((kwq->kw_ksynqueues[KSYN_QUEUE_READ].ksynq_count != 0) || ((flags & KW_UNLOCK_PREPOST_READLOCK) != 0)) {
                type |= PTH_RWSHFT_TYPE_READ;
                /* read entries are present */
                if (kwq->kw_ksynqueues[KSYN_QUEUE_READ].ksynq_count != 0) {
                        kw_fr = kwq->kw_ksynqueues[KSYN_QUEUE_READ].ksynq_firstnum;
                        if (((flags & KW_UNLOCK_PREPOST_READLOCK) != 0) && (is_seqlower(premgen, kw_fr) != 0))
                                kw_fr = premgen;
                } else
                        kw_fr = premgen;
                
                lowest[KSYN_QUEUE_READ] = kw_fr;
                numbers[count]= kw_fr;
                typenum[count] = PTH_RW_TYPE_READ;
                count++;
        } else
                lowest[KSYN_QUEUE_READ] = 0;
        
        if ((kwq->kw_ksynqueues[KSYN_QUEUE_WRITER].ksynq_count != 0) || ((flags & KW_UNLOCK_PREPOST_WRLOCK) != 0)) {
                type |= PTH_RWSHFT_TYPE_WRITE;
                /* read entries are present */
                if (kwq->kw_ksynqueues[KSYN_QUEUE_WRITER].ksynq_count != 0) {
                        kw_fwr = kwq->kw_ksynqueues[KSYN_QUEUE_WRITER].ksynq_firstnum;
                        if (((flags & KW_UNLOCK_PREPOST_WRLOCK) != 0) && (is_seqlower(premgen, kw_fwr) != 0))
                                kw_fwr = premgen;
                } else
                        kw_fwr = premgen;
                
                lowest[KSYN_QUEUE_WRITER] = kw_fwr;
                numbers[count]= kw_fwr;
                typenum[count] = PTH_RW_TYPE_WRITE;
                count++;
        } else
                lowest[KSYN_QUEUE_WRITER] = 0;
        
#if __TESTPANICS__
        if (count == 0)
                panic("nothing in the queue???\n");
#endif /* __TESTPANICS__ */
        
        low = numbers[0];
        lowtype = typenum[0];
        if (count > 1) {
                for (i = 1; i< count; i++) {
                        if (is_seqlower(numbers[i] , low) != 0) {
                                low = numbers[i];
                                lowtype = typenum[i];
                        }
                }
        }
        type |= lowtype;
        
        if (typep != 0)
                *typep = type;
        return(0);
}

/* wakeup readers to upto the writer limits */
int
ksyn_wakeupreaders(ksyn_wait_queue_t kwq, uint32_t limitread, int allreaders, uint32_t updatebits, int *wokenp)
{
        ksyn_queue_t kq;
        int failedwakeup = 0;
        int numwoken = 0;
        kern_return_t kret = KERN_SUCCESS;
        uint32_t lbits = 0;
        
        lbits = updatebits;
        
        kq = &kwq->kw_ksynqueues[KSYN_QUEUE_READ];
        while ((kq->ksynq_count != 0) && (allreaders || (is_seqlower(kq->ksynq_firstnum, limitread) != 0))) {
                kret = ksyn_signal(kwq, KSYN_QUEUE_READ, NULL, lbits);
                if (kret == KERN_NOT_WAITING) {
                        failedwakeup++;
                }
                numwoken++;
        }
        
        if (wokenp != NULL)
                *wokenp = numwoken;
        return(failedwakeup);
}


/* This handles the unlock grants for next set on rw_unlock() or on arrival of all preposted waiters */
int
kwq_handle_unlock(ksyn_wait_queue_t kwq,
                  __unused uint32_t mgen,
                  uint32_t rw_wc,
                  uint32_t *updatep,
                  int flags,
                  int *blockp,
                  uint32_t premgen)
{
        uint32_t low_writer, limitrdnum;
        int rwtype, error=0;
        int allreaders, failed;
        uint32_t updatebits=0, numneeded = 0;;
        int prepost = flags & KW_UNLOCK_PREPOST;
        thread_t preth = THREAD_NULL;
        ksyn_waitq_element_t kwe;
        uthread_t uth;
        thread_t th;
        int woken = 0;
        int block = 1;
        uint32_t lowest[KSYN_QUEUE_MAX]; /* np need for upgrade as it is handled separately */
        kern_return_t kret = KERN_SUCCESS;
        ksyn_queue_t kq;
        int curthreturns = 0;
        
        if (prepost != 0) {
                preth = current_thread();
        }
        
        kq = &kwq->kw_ksynqueues[KSYN_QUEUE_READ];
        kwq->kw_lastseqword = rw_wc;
        kwq->kw_lastunlockseq = (rw_wc & PTHRW_COUNT_MASK);
        kwq->kw_overlapwatch = 0;
        
        error = kwq_find_rw_lowest(kwq, flags, premgen, &rwtype, lowest);
#if __TESTPANICS__
        if (error != 0)
                panic("rwunlock: cannot fails to slot next round of threads");
#endif /* __TESTPANICS__ */
        
        low_writer = lowest[KSYN_QUEUE_WRITER];
        
        allreaders = 0;
        updatebits = 0;
        
        switch (rwtype & PTH_RW_TYPE_MASK) {
                case PTH_RW_TYPE_READ: {
                        // XXX
                        /* what about the preflight which is LREAD or READ ?? */
                        if ((rwtype & PTH_RWSHFT_TYPE_MASK) != 0) {
                                if (rwtype & PTH_RWSHFT_TYPE_WRITE) {
                                        updatebits |= (PTH_RWL_WBIT | PTH_RWL_KBIT);
                                }
                        }
                        limitrdnum = 0;
                        if ((rwtype & PTH_RWSHFT_TYPE_WRITE) != 0) {
                                limitrdnum = low_writer;
                        } else {
                                allreaders = 1;
                        }
                        
                        numneeded = 0;
                        
                        if ((rwtype & PTH_RWSHFT_TYPE_WRITE) != 0) {
                                limitrdnum = low_writer;
                                numneeded = ksyn_queue_count_tolowest(kq, limitrdnum);
                                if (((flags & KW_UNLOCK_PREPOST_READLOCK) != 0) && (is_seqlower(premgen, limitrdnum) != 0)) {
                                        curthreturns = 1;
                                        numneeded += 1;
                                }
                        } else {
                                // no writers at all
                                // no other waiters only readers
                                kwq->kw_overlapwatch = 1;
                                numneeded += kwq->kw_ksynqueues[KSYN_QUEUE_READ].ksynq_count;
                                if ((flags & KW_UNLOCK_PREPOST_READLOCK) != 0) {
                                        curthreturns = 1;
                                        numneeded += 1;
                                }
                        }
                        
                        updatebits += (numneeded << PTHRW_COUNT_SHIFT);
                        
                        kwq->kw_nextseqword = (rw_wc & PTHRW_COUNT_MASK) + updatebits;
                        
                        if (curthreturns != 0) {
                                block = 0;
                                uth = current_uthread();
                                kwe = pthread_kern->uthread_get_uukwe(uth);
                                kwe->kwe_psynchretval = updatebits;
                        }
                        
                        
                        failed = ksyn_wakeupreaders(kwq, limitrdnum, allreaders, updatebits, &woken);
                        if (failed != 0) {
                                kwq->kw_pre_intrcount = failed; /* actually a count */
                                kwq->kw_pre_intrseq = limitrdnum;
                                kwq->kw_pre_intrretbits = updatebits;
                                kwq->kw_pre_intrtype = PTH_RW_TYPE_READ;
                        }
                        
                        error = 0;
                        
                        if ((kwq->kw_ksynqueues[KSYN_QUEUE_WRITER].ksynq_count != 0) && ((updatebits & PTH_RWL_WBIT) == 0))
                                panic("kwq_handle_unlock: writer pending but no writebit set %x\n", updatebits);
                }
                        break;
                        
                case PTH_RW_TYPE_WRITE: {
                        
                        /* only one thread is goin to be granted */
                        updatebits |= (PTHRW_INC);
                        updatebits |= PTH_RWL_KBIT| PTH_RWL_EBIT;
                        
                        if (((flags & KW_UNLOCK_PREPOST_WRLOCK) != 0) && (low_writer == premgen)) {
                                block = 0;
                                if (kwq->kw_ksynqueues[KSYN_QUEUE_WRITER].ksynq_count != 0) {
                                        updatebits |= PTH_RWL_WBIT;
                                }
                                th = preth;
                                uth = pthread_kern->get_bsdthread_info(th);
                                kwe = pthread_kern->uthread_get_uukwe(uth);
                                kwe->kwe_psynchretval = updatebits;
                        } else {
                                /* we are not granting writelock to the preposting thread */
                                /* if there are writers present or the preposting write thread then W bit is to be set */
                                if (kwq->kw_ksynqueues[KSYN_QUEUE_WRITER].ksynq_count > 1 ||
                                    (flags & KW_UNLOCK_PREPOST_WRLOCK) != 0) {
                                        updatebits |= PTH_RWL_WBIT;
                                }
                                /* setup next in the queue */
                                kret = ksyn_signal(kwq, KSYN_QUEUE_WRITER, NULL, updatebits);
                                if (kret == KERN_NOT_WAITING) {
                                        kwq->kw_pre_intrcount = 1;      /* actually a count */
                                        kwq->kw_pre_intrseq = low_writer;
                                        kwq->kw_pre_intrretbits = updatebits;
                                        kwq->kw_pre_intrtype = PTH_RW_TYPE_WRITE;
                                }
                                error = 0;
                        }
                        kwq->kw_nextseqword = (rw_wc & PTHRW_COUNT_MASK) + updatebits;
                        if ((updatebits & (PTH_RWL_KBIT | PTH_RWL_EBIT)) != (PTH_RWL_KBIT | PTH_RWL_EBIT))
                                panic("kwq_handle_unlock: writer lock granted but no ke set %x\n", updatebits);
                }
                        break;
                        
                default:
                        panic("rwunlock: invalid type for lock grants");
                        
        };
        
        if (updatep != NULL)
                *updatep = updatebits;
        if (blockp != NULL)
                *blockp = block;
        return(error);
}

/************* Indiv queue support routines ************************/
void
ksyn_queue_init(ksyn_queue_t kq)
{
        TAILQ_INIT(&kq->ksynq_kwelist);
        kq->ksynq_count = 0;
        kq->ksynq_firstnum = 0;
        kq->ksynq_lastnum = 0;
}

int
ksyn_queue_insert(ksyn_wait_queue_t kwq, int kqi, ksyn_waitq_element_t kwe, uint32_t mgen, int fit)
{
        ksyn_queue_t kq = &kwq->kw_ksynqueues[kqi];
        uint32_t lockseq = mgen & PTHRW_COUNT_MASK;
        int res = 0;

        if (kwe->kwe_kwqqueue != NULL) {
                panic("adding enqueued item to another queue");
        }

        if (kq->ksynq_count == 0) {
                TAILQ_INSERT_HEAD(&kq->ksynq_kwelist, kwe, kwe_list);
                kq->ksynq_firstnum = lockseq;
                kq->ksynq_lastnum = lockseq;
        } else if (fit == FIRSTFIT) {
                /* TBD: if retry bit is set for mutex, add it to the head */
                /* firstfit, arriving order */
                TAILQ_INSERT_TAIL(&kq->ksynq_kwelist, kwe, kwe_list);
                if (is_seqlower(lockseq, kq->ksynq_firstnum)) {
                        kq->ksynq_firstnum = lockseq;
                }
                if (is_seqhigher(lockseq, kq->ksynq_lastnum)) {
                        kq->ksynq_lastnum = lockseq;
                }
        } else if (lockseq == kq->ksynq_firstnum || lockseq == kq->ksynq_lastnum) {
                /* During prepost when a thread is getting cancelled, we could have two with same seq */
                res = EBUSY;
                if (kwe->kwe_state == KWE_THREAD_PREPOST) {
                        ksyn_waitq_element_t tmp = ksyn_queue_find_seq(kwq, kq, lockseq);
                        if (tmp != NULL && tmp->kwe_uth != NULL && pthread_kern->uthread_is_cancelled(tmp->kwe_uth)) {
                                TAILQ_INSERT_TAIL(&kq->ksynq_kwelist, kwe, kwe_list);
                                res = 0;
                        }
                }
        } else if (is_seqlower(kq->ksynq_lastnum, lockseq)) { // XXX is_seqhigher
                TAILQ_INSERT_TAIL(&kq->ksynq_kwelist, kwe, kwe_list);
                kq->ksynq_lastnum = lockseq;
        } else if (is_seqlower(lockseq, kq->ksynq_firstnum)) {
                TAILQ_INSERT_HEAD(&kq->ksynq_kwelist, kwe, kwe_list);
                kq->ksynq_firstnum = lockseq;
        } else {
                ksyn_waitq_element_t q_kwe, r_kwe;
                
                res = ESRCH;
                TAILQ_FOREACH_SAFE(q_kwe, &kq->ksynq_kwelist, kwe_list, r_kwe) {
                        if (is_seqhigher(q_kwe->kwe_lockseq, lockseq)) {
                                TAILQ_INSERT_BEFORE(q_kwe, kwe, kwe_list);
                                res = 0;
                                break;
                        }
                }
        }
        
        if (res == 0) {
                kwe->kwe_kwqqueue = kwq;
                kq->ksynq_count++;
                kwq->kw_inqueue++;
                update_low_high(kwq, lockseq);
        }
        return res;
}

void
ksyn_queue_remove_item(ksyn_wait_queue_t kwq, ksyn_queue_t kq, ksyn_waitq_element_t kwe)
{
        if (kq->ksynq_count == 0) {
                panic("removing item from empty queue");
        }

        if (kwe->kwe_kwqqueue != kwq) {
                panic("removing item from wrong queue");
        }

        TAILQ_REMOVE(&kq->ksynq_kwelist, kwe, kwe_list);
        kwe->kwe_list.tqe_next = NULL;
        kwe->kwe_list.tqe_prev = NULL;
        kwe->kwe_kwqqueue = NULL;
        
        if (--kq->ksynq_count > 0) {
                ksyn_waitq_element_t tmp;
                tmp = TAILQ_FIRST(&kq->ksynq_kwelist);
                kq->ksynq_firstnum = tmp->kwe_lockseq & PTHRW_COUNT_MASK;
                tmp = TAILQ_LAST(&kq->ksynq_kwelist, ksynq_kwelist_head);
                kq->ksynq_lastnum = tmp->kwe_lockseq & PTHRW_COUNT_MASK;
        } else {
                kq->ksynq_firstnum = 0;
                kq->ksynq_lastnum = 0;
        }
        
        if (--kwq->kw_inqueue > 0) {
                uint32_t curseq = kwe->kwe_lockseq & PTHRW_COUNT_MASK;
                if (kwq->kw_lowseq == curseq) {
                        kwq->kw_lowseq = find_nextlowseq(kwq);
                }
                if (kwq->kw_highseq == curseq) {
                        kwq->kw_highseq = find_nexthighseq(kwq);
                }
        } else {
                kwq->kw_lowseq = 0;
                kwq->kw_highseq = 0;
        }
}

ksyn_waitq_element_t
ksyn_queue_find_seq(__unused ksyn_wait_queue_t kwq, ksyn_queue_t kq, uint32_t seq)
{
        ksyn_waitq_element_t kwe;
        
        // XXX: should stop searching when higher sequence number is seen
        TAILQ_FOREACH(kwe, &kq->ksynq_kwelist, kwe_list) {
                if ((kwe->kwe_lockseq & PTHRW_COUNT_MASK) == seq) {
                        return kwe;
                }
        }
        return NULL;
}

/* find the thread at the target sequence (or a broadcast/prepost at or above) */
ksyn_waitq_element_t
ksyn_queue_find_cvpreposeq(ksyn_queue_t kq, uint32_t cgen)
{
        ksyn_waitq_element_t result = NULL;
        ksyn_waitq_element_t kwe;
        uint32_t lgen = (cgen & PTHRW_COUNT_MASK);
        
        TAILQ_FOREACH(kwe, &kq->ksynq_kwelist, kwe_list) {
                if (is_seqhigher_eq(kwe->kwe_lockseq, cgen)) {
                        result = kwe;
                        
                        // KWE_THREAD_INWAIT must be strictly equal
                        if (kwe->kwe_state == KWE_THREAD_INWAIT && (kwe->kwe_lockseq & PTHRW_COUNT_MASK) != lgen) {
                                result = NULL;
                        }
                        break;
                }
        }
        return result;
}

/* look for a thread at lockseq, a */
ksyn_waitq_element_t
ksyn_queue_find_signalseq(__unused ksyn_wait_queue_t kwq, ksyn_queue_t kq, uint32_t uptoseq, uint32_t signalseq)
{
        ksyn_waitq_element_t result = NULL;
        ksyn_waitq_element_t q_kwe, r_kwe;
        
        // XXX
        /* case where wrap in the tail of the queue exists */
        TAILQ_FOREACH_SAFE(q_kwe, &kq->ksynq_kwelist, kwe_list, r_kwe) {
                if (q_kwe->kwe_state == KWE_THREAD_PREPOST) {
                        if (is_seqhigher(q_kwe->kwe_lockseq, uptoseq)) {
                                return result;
                        }
                }
                if (q_kwe->kwe_state == KWE_THREAD_PREPOST || q_kwe->kwe_state == KWE_THREAD_BROADCAST) {
                        /* match any prepost at our same uptoseq or any broadcast above */
                        if (is_seqlower(q_kwe->kwe_lockseq, uptoseq)) {
                                continue;
                        }
                        return q_kwe;
                } else if (q_kwe->kwe_state == KWE_THREAD_INWAIT) {
                        /*
                         * Match any (non-cancelled) thread at or below our upto sequence -
                         * but prefer an exact match to our signal sequence (if present) to
                         * keep exact matches happening.
                         */
                        if (is_seqhigher(q_kwe->kwe_lockseq, uptoseq)) {
                                return result;
                        }
                        if (q_kwe->kwe_kwqqueue == kwq) {
                                if (!pthread_kern->uthread_is_cancelled(q_kwe->kwe_uth)) {
                                        /* if equal or higher than our signal sequence, return this one */
                                        if (is_seqhigher_eq(q_kwe->kwe_lockseq, signalseq)) {
                                                return q_kwe;
                                        }
                                        
                                        /* otherwise, just remember this eligible thread and move on */
                                        if (result == NULL) {
                                                result = q_kwe;
                                        }
                                }
                        }
                } else {
                        panic("ksyn_queue_find_signalseq(): unknown wait queue element type (%d)\n", q_kwe->kwe_state);
                }
        }
        return result;
}

void
ksyn_queue_free_items(ksyn_wait_queue_t kwq, int kqi, uint32_t upto, int all)
{
        ksyn_waitq_element_t kwe;
        uint32_t tseq = upto & PTHRW_COUNT_MASK;
        ksyn_queue_t kq = &kwq->kw_ksynqueues[kqi];
        
        while ((kwe = TAILQ_FIRST(&kq->ksynq_kwelist)) != NULL) {
                if (all == 0 && is_seqhigher(kwe->kwe_lockseq, tseq)) {
                        break;
                }
                if (kwe->kwe_state == KWE_THREAD_INWAIT) {
                        /*
                         * This scenario is typically noticed when the cvar is
                         * reinited and the new waiters are waiting. We can
                         * return them as spurious wait so the cvar state gets
                         * reset correctly.
                         */
                        
                        /* skip canceled ones */
                        /* wake the rest */
                        /* set M bit to indicate to waking CV to retun Inc val */
                        (void)ksyn_signal(kwq, kqi, kwe, PTHRW_INC | PTH_RWS_CV_MBIT | PTH_RWL_MTX_WAIT);
                } else {
                        ksyn_queue_remove_item(kwq, kq, kwe);
                        pthread_kern->zfree(kwe_zone, kwe);
                        kwq->kw_fakecount--;
                }
        }
}

/*************************************************************************/

void
update_low_high(ksyn_wait_queue_t kwq, uint32_t lockseq)
{
        if (kwq->kw_inqueue == 1) {
                kwq->kw_lowseq = lockseq;
                kwq->kw_highseq = lockseq;
        } else {
                if (is_seqlower(lockseq, kwq->kw_lowseq)) {
                        kwq->kw_lowseq = lockseq;
                }
                if (is_seqhigher(lockseq, kwq->kw_highseq)) {
                        kwq->kw_highseq = lockseq;
                }
        }
}

uint32_t
find_nextlowseq(ksyn_wait_queue_t kwq)
{
        uint32_t lowest = 0;
        int first = 1;
        int i;
        
        for (i = 0; i < KSYN_QUEUE_MAX; i++) {
                if (kwq->kw_ksynqueues[i].ksynq_count > 0) {
                        uint32_t current = kwq->kw_ksynqueues[i].ksynq_firstnum;
                        if (first || is_seqlower(current, lowest)) {
                                lowest = current;
                                first = 0;
                        }
                }
        }
        
        return lowest;
}

uint32_t
find_nexthighseq(ksyn_wait_queue_t kwq)
{
        uint32_t highest = 0;
        int first = 1;
        int i;
        
        for (i = 0; i < KSYN_QUEUE_MAX; i++) {
                if (kwq->kw_ksynqueues[i].ksynq_count > 0) {
                        uint32_t current = kwq->kw_ksynqueues[i].ksynq_lastnum;
                        if (first || is_seqhigher(current, highest)) {
                                highest = current;
                                first = 0;
                        }
                }
        }
        
        return highest;
}

int
find_seq_till(ksyn_wait_queue_t kwq, uint32_t upto, uint32_t nwaiters, uint32_t *countp)
{
        int i;
        uint32_t count = 0;
        
        for (i = 0; i< KSYN_QUEUE_MAX; i++) {
                count += ksyn_queue_count_tolowest(&kwq->kw_ksynqueues[i], upto);
                if (count >= nwaiters) {
                        break;
                }
        }
        
        if (countp != NULL) {
                *countp = count;
        }
        
        if (count == 0) {
                return 0;
        } else if (count >= nwaiters) {
                return 1;
        } else {
                return 0;
        }
}


uint32_t
ksyn_queue_count_tolowest(ksyn_queue_t kq, uint32_t upto)
{
        uint32_t i = 0;
        ksyn_waitq_element_t kwe, newkwe;
        
        if (kq->ksynq_count == 0 || is_seqhigher(kq->ksynq_firstnum, upto)) {
                return 0;
        }
        if (upto == kq->ksynq_firstnum) {
                return 1;
        }
        TAILQ_FOREACH_SAFE(kwe, &kq->ksynq_kwelist, kwe_list, newkwe) {
                uint32_t curval = (kwe->kwe_lockseq & PTHRW_COUNT_MASK);
                if (is_seqhigher(curval, upto)) {
                        break;
                }
                ++i;
                if (upto == curval) {
                        break;
                }
        }
        return i;
}

/* handles the cond broadcast of cvar and returns number of woken threads and bits for syscall return */
void
ksyn_handle_cvbroad(ksyn_wait_queue_t ckwq, uint32_t upto, uint32_t *updatep)
{
        ksyn_waitq_element_t kwe, newkwe;
        uint32_t updatebits = 0;
        ksyn_queue_t kq = &ckwq->kw_ksynqueues[KSYN_QUEUE_WRITER];
        
        struct ksyn_queue kfreeq;
        ksyn_queue_init(&kfreeq);
        
retry:
        TAILQ_FOREACH_SAFE(kwe, &kq->ksynq_kwelist, kwe_list, newkwe) {
                if (is_seqhigher(kwe->kwe_lockseq, upto)) {
                        // outside our range
                        break;
                }

                if (kwe->kwe_state == KWE_THREAD_INWAIT) {
                        // Wake only non-canceled threads waiting on this CV.
                        if (!pthread_kern->uthread_is_cancelled(kwe->kwe_uth)) {
                                (void)ksyn_signal(ckwq, KSYN_QUEUE_WRITER, kwe, PTH_RWL_MTX_WAIT);
                                updatebits += PTHRW_INC;
                        }
                } else if (kwe->kwe_state == KWE_THREAD_BROADCAST ||
                           kwe->kwe_state == KWE_THREAD_PREPOST) {
                        ksyn_queue_remove_item(ckwq, kq, kwe);
                        TAILQ_INSERT_TAIL(&kfreeq.ksynq_kwelist, kwe, kwe_list);
                        ckwq->kw_fakecount--;
                } else {
                        panic("unknown kwe state\n");
                }
        }
        
        /* Need to enter a broadcast in the queue (if not already at L == S) */
        
        if (diff_genseq(ckwq->kw_lword, ckwq->kw_sword)) {
                newkwe = TAILQ_FIRST(&kfreeq.ksynq_kwelist);
                if (newkwe == NULL) {
                        ksyn_wqunlock(ckwq);
                        newkwe = (ksyn_waitq_element_t)pthread_kern->zalloc(kwe_zone);
                        TAILQ_INSERT_TAIL(&kfreeq.ksynq_kwelist, newkwe, kwe_list);
                        ksyn_wqlock(ckwq);
                        goto retry;
                } else {
                        TAILQ_REMOVE(&kfreeq.ksynq_kwelist, newkwe, kwe_list);
                        ksyn_prepost(ckwq, newkwe, KWE_THREAD_BROADCAST, upto);
                }
        }
        
        // free up any remaining things stumbled across above
        while ((kwe = TAILQ_FIRST(&kfreeq.ksynq_kwelist)) != NULL) {
                TAILQ_REMOVE(&kfreeq.ksynq_kwelist, kwe, kwe_list);
                pthread_kern->zfree(kwe_zone, kwe);
        }
        
        if (updatep != NULL) {
                *updatep = updatebits;
        }
}

void
ksyn_cvupdate_fixup(ksyn_wait_queue_t ckwq, uint32_t *updatebits)
{
        if ((ckwq->kw_lword & PTHRW_COUNT_MASK) == (ckwq->kw_sword & PTHRW_COUNT_MASK)) {
                if (ckwq->kw_inqueue != 0) {
                        /* FREE THE QUEUE */
                        ksyn_queue_free_items(ckwq, KSYN_QUEUE_WRITER, ckwq->kw_lword, 0);
#if __TESTPANICS__
                        if (ckwq->kw_inqueue != 0)
                                panic("ksyn_cvupdate_fixup: L == S, but entries in queue beyond S");
#endif /* __TESTPANICS__ */
                }
                ckwq->kw_lword = ckwq->kw_uword = ckwq->kw_sword = 0;
                ckwq->kw_kflags |= KSYN_KWF_ZEROEDOUT;
                *updatebits |= PTH_RWS_CV_CBIT;
        } else if (ckwq->kw_inqueue != 0 && ckwq->kw_fakecount == ckwq->kw_inqueue) {
                // only fake entries are present in the queue
                *updatebits |= PTH_RWS_CV_PBIT;
        }
}

void
psynch_zoneinit(void)
{
        kwq_zone = (zone_t)pthread_kern->zinit(sizeof(struct ksyn_wait_queue), 8192 * sizeof(struct ksyn_wait_queue), 4096, "ksyn_wait_queue");
        kwe_zone = (zone_t)pthread_kern->zinit(sizeof(struct ksyn_waitq_element), 8192 * sizeof(struct ksyn_waitq_element), 4096, "ksyn_waitq_element");
}

void *
_pthread_get_thread_kwq(thread_t thread)
{
        assert(thread);
        struct uthread * uthread = pthread_kern->get_bsdthread_info(thread);
        assert(uthread);
        ksyn_waitq_element_t kwe = pthread_kern->uthread_get_uukwe(uthread);
        assert(kwe);
        ksyn_wait_queue_t kwq = kwe->kwe_kwqqueue;
        return kwq;
}

/* This function is used by stackshot to determine why a thread is blocked, and report
 * who owns the object that the thread is blocked on. It should *only* be called if the
 * `block_hint' field in the relevant thread's struct is populated with something related
 * to pthread sync objects.
 */
void
_pthread_find_owner(thread_t thread, struct stackshot_thread_waitinfo * waitinfo)
{
        ksyn_wait_queue_t kwq = _pthread_get_thread_kwq(thread);
        switch (waitinfo->wait_type) {
                case kThreadWaitPThreadMutex:
                        assert((kwq->kw_type & KSYN_WQTYPE_MASK) == KSYN_WQTYPE_MTX);
                        waitinfo->owner   = kwq->kw_owner;
                        waitinfo->context = kwq->kw_addr;
                        break;
                /* Owner of rwlock not stored in kernel space due to races. Punt
                 * and hope that the userspace address is helpful enough. */
                case kThreadWaitPThreadRWLockRead:
                case kThreadWaitPThreadRWLockWrite:
                        assert((kwq->kw_type & KSYN_WQTYPE_MASK) == KSYN_WQTYPE_RWLOCK);
                        waitinfo->owner   = 0;
                        waitinfo->context = kwq->kw_addr;
                        break;
                /* Condvars don't have owners, so just give the userspace address. */
                case kThreadWaitPThreadCondVar:
                        assert((kwq->kw_type & KSYN_WQTYPE_MASK) == KSYN_WQTYPE_CVAR);
                        waitinfo->owner   = 0;
                        waitinfo->context = kwq->kw_addr;
                        break;
                case kThreadWaitNone:
                default:
                        waitinfo->owner = 0;
                        waitinfo->context = 0;
                        break;
        }
}