src/shims/yield.h

   1 /*
   2  * Copyright (c) 2013 Apple Inc. All rights reserved.
   3  *
   4  * @APPLE_APACHE_LICENSE_HEADER_START@
   5  *
   6  * Licensed under the Apache License, Version 2.0 (the "License");
   7  * you may not use this file except in compliance with the License.
   8  * You may obtain a copy of the License at
   9  *
  10  *     http://www.apache.org/licenses/LICENSE-2.0
  11  *
  12  * Unless required by applicable law or agreed to in writing, software
  13  * distributed under the License is distributed on an "AS IS" BASIS,
  14  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  15  * See the License for the specific language governing permissions and
  16  * limitations under the License.
  17  *
  18  * @APPLE_APACHE_LICENSE_HEADER_END@
  19  */
  20
  21 /*
  22  * IMPORTANT: This header file describes INTERNAL interfaces to libdispatch
  23  * which are subject to change in future releases of Mac OS X. Any applications
  24  * relying on these interfaces WILL break.
  25  */
  26
  27 #ifndef __DISPATCH_SHIMS_YIELD__
  28 #define __DISPATCH_SHIMS_YIELD__
  29
  30 #pragma mark -
  31 #pragma mark _dispatch_wait_until
  32
  33 #if DISPATCH_HW_CONFIG_UP
  34 #define _dispatch_wait_until(c) ({ \
  35                 typeof(c) _c; \
  36                 int _spins = 0; \
  37                 for (;;) { \
  38                         if (likely(_c = (c))) break; \
  39                         _spins++; \
  40                         _dispatch_preemption_yield(_spins); \
  41                 } \
  42                 _c; })
  43 #elif TARGET_OS_EMBEDDED
  44 // <rdar://problem/15440575>
  45 #ifndef DISPATCH_WAIT_SPINS
  46 #define DISPATCH_WAIT_SPINS 1024
  47 #endif
  48 #define _dispatch_wait_until(c) ({ \
  49                 typeof(c) _c; \
  50                 int _spins = -(DISPATCH_WAIT_SPINS); \
  51                 for (;;) { \
  52                         if (likely(_c = (c))) break; \
  53                         if (slowpath(_spins++ >= 0)) { \
  54                                 _dispatch_preemption_yield(_spins); \
  55                         } else { \
  56                                 dispatch_hardware_pause(); \
  57                         } \
  58                 } \
  59                 _c; })
  60 #else
  61 #define _dispatch_wait_until(c) ({ \
  62                 typeof(c) _c; \
  63                 for (;;) { \
  64                         if (likely(_c = (c))) break; \
  65                         dispatch_hardware_pause(); \
  66                 } \
  67                 _c; })
  68 #endif
  69
  70 #pragma mark -
  71 #pragma mark _dispatch_contention_wait_until
  72
  73 #if DISPATCH_HW_CONFIG_UP
  74 #define _dispatch_contention_wait_until(c) false
  75 #else
  76 #ifndef DISPATCH_CONTENTION_SPINS_MAX
  77 #define DISPATCH_CONTENTION_SPINS_MAX (128 - 1)
  78 #endif
  79 #ifndef DISPATCH_CONTENTION_SPINS_MIN
  80 #define DISPATCH_CONTENTION_SPINS_MIN (32 - 1)
  81 #endif
  82 #if TARGET_OS_EMBEDDED
  83 #define _dispatch_contention_spins() \
  84                 ((DISPATCH_CONTENTION_SPINS_MIN) + ((DISPATCH_CONTENTION_SPINS_MAX) - \
  85                 (DISPATCH_CONTENTION_SPINS_MIN)) / 2)
  86 #else
  87 // Use randomness to prevent threads from resonating at the same
  88 // frequency and permanently contending. All threads sharing the same
  89 // seed value is safe with the FreeBSD rand_r implementation.
  90 #define _dispatch_contention_spins() ({ \
  91                 static unsigned int _seed; \
  92                 ((unsigned int)rand_r(&_seed) & (DISPATCH_CONTENTION_SPINS_MAX)) | \
  93                                 (DISPATCH_CONTENTION_SPINS_MIN); })
  94 #endif
  95 #define _dispatch_contention_wait_until(c) ({ \
  96                 bool _out = false; \
  97                 unsigned int _spins = _dispatch_contention_spins(); \
  98                 while (_spins--) { \
  99                         dispatch_hardware_pause(); \
 100                         if ((_out = fastpath(c))) break; \
 101                 }; _out; })
 102 #endif
 103
 104 #pragma mark -
 105 #pragma mark dispatch_hardware_pause
 106
 107 #if defined(__x86_64__) || defined(__i386__)
 108 #define dispatch_hardware_pause() __asm__("pause")
 109 #elif (defined(__arm__) && defined(_ARM_ARCH_7) && defined(__thumb__)) || \
 110                 defined(__arm64__)
 111 #define dispatch_hardware_pause() __asm__("yield")
 112 #define dispatch_hardware_wfe()   __asm__("wfe")
 113 #else
 114 #define dispatch_hardware_pause() __asm__("")
 115 #endif
 116
 117 #pragma mark -
 118 #pragma mark _dispatch_preemption_yield
 119
 120 #if HAVE_MACH
 121 #if defined(SWITCH_OPTION_OSLOCK_DEPRESS)
 122 #define DISPATCH_YIELD_THREAD_SWITCH_OPTION SWITCH_OPTION_OSLOCK_DEPRESS
 123 #else
 124 #define DISPATCH_YIELD_THREAD_SWITCH_OPTION SWITCH_OPTION_DEPRESS
 125 #endif
 126 #define _dispatch_preemption_yield(n) thread_switch(MACH_PORT_NULL, \
 127                 DISPATCH_YIELD_THREAD_SWITCH_OPTION, (mach_msg_timeout_t)(n))
 128 #define _dispatch_preemption_yield_to(th, n) thread_switch(th, \
 129                 DISPATCH_YIELD_THREAD_SWITCH_OPTION, (mach_msg_timeout_t)(n))
 130 #else
 131 #define _dispatch_preemption_yield(n) pthread_yield_np()
 132 #define _dispatch_preemption_yield_to(th, n) pthread_yield_np()
 133 #endif // HAVE_MACH
 134
 135 #pragma mark -
 136 #pragma mark _dispatch_contention_usleep
 137
 138 #ifndef DISPATCH_CONTENTION_USLEEP_START
 139 #define DISPATCH_CONTENTION_USLEEP_START 500
 140 #endif
 141 #ifndef DISPATCH_CONTENTION_USLEEP_MAX
 142 #define DISPATCH_CONTENTION_USLEEP_MAX 100000
 143 #endif
 144
 145 #if HAVE_MACH
 146 #if defined(SWITCH_OPTION_DISPATCH_CONTENTION)
 147 #define _dispatch_contention_usleep(u) thread_switch(MACH_PORT_NULL, \
 148                 SWITCH_OPTION_DISPATCH_CONTENTION, (u))
 149 #else
 150 #define _dispatch_contention_usleep(u) thread_switch(MACH_PORT_NULL, \
 151                 SWITCH_OPTION_WAIT, (((u)-1)/1000)+1)
 152 #endif
 153 #else
 154 #define _dispatch_contention_usleep(u) usleep((u))
 155 #endif // HAVE_MACH
 156
 157 #endif // __DISPATCH_SHIMS_YIELD__