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) do { \
  35                 int _spins = 0; \
  36                 while (!(c)) { \
  37                         _spins++; \
  38                         _dispatch_preemption_yield(_spins); \
  39                 } } while (0)
  40 #elif TARGET_OS_EMBEDDED
  41 // <rdar://problem/15440575>
  42 #ifndef DISPATCH_WAIT_SPINS
  43 #define DISPATCH_WAIT_SPINS 1024
  44 #endif
  45 #define _dispatch_wait_until(c) do { \
  46                 int _spins = -(DISPATCH_WAIT_SPINS); \
  47                 while (!(c)) { \
  48                         if (slowpath(_spins++ >= 0)) { \
  49                                 _dispatch_preemption_yield(_spins); \
  50                         } else { \
  51                                 dispatch_hardware_pause(); \
  52                         } \
  53                 } } while (0)
  54 #else
  55 #define _dispatch_wait_until(c) do { \
  56                 while (!(c)) { \
  57                         dispatch_hardware_pause(); \
  58                 } } while (0)
  59 #endif
  60
  61 #pragma mark -
  62 #pragma mark _dispatch_contention_wait_until
  63
  64 #if DISPATCH_HW_CONFIG_UP
  65 #define _dispatch_contention_wait_until(c) false
  66 #else
  67 #ifndef DISPATCH_CONTENTION_SPINS_MAX
  68 #define DISPATCH_CONTENTION_SPINS_MAX (128 - 1)
  69 #endif
  70 #ifndef DISPATCH_CONTENTION_SPINS_MIN
  71 #define DISPATCH_CONTENTION_SPINS_MIN (32 - 1)
  72 #endif
  73 #if TARGET_OS_EMBEDDED
  74 #define _dispatch_contention_spins() \
  75                 ((DISPATCH_CONTENTION_SPINS_MIN) + ((DISPATCH_CONTENTION_SPINS_MAX) - \
  76                 (DISPATCH_CONTENTION_SPINS_MIN)) / 2)
  77 #else
  78 // Use randomness to prevent threads from resonating at the same
  79 // frequency and permanently contending. All threads sharing the same
  80 // seed value is safe with the FreeBSD rand_r implementation.
  81 #define _dispatch_contention_spins() ({ \
  82                 static unsigned int _seed; \
  83                 ((unsigned int)rand_r(&_seed) & (DISPATCH_CONTENTION_SPINS_MAX)) | \
  84                                 (DISPATCH_CONTENTION_SPINS_MIN); })
  85 #endif
  86 #define _dispatch_contention_wait_until(c) ({ \
  87                 bool _out = false; \
  88                 unsigned int _spins = _dispatch_contention_spins(); \
  89                 while (_spins--) { \
  90                         dispatch_hardware_pause(); \
  91                         if ((_out = fastpath(c))) break; \
  92                 }; _out; })
  93 #endif
  94
  95 #pragma mark -
  96 #pragma mark dispatch_hardware_pause
  97
  98 #if defined(__x86_64__) || defined(__i386__)
  99 #define dispatch_hardware_pause() __asm__("pause")
 100 #elif (defined(__arm__) && defined(_ARM_ARCH_7) && defined(__thumb__)) || \
 101                 defined(__arm64__)
 102 #define dispatch_hardware_pause() __asm__("yield")
 103 #define dispatch_hardware_wfe()   __asm__("wfe")
 104 #else
 105 #define dispatch_hardware_pause() __asm__("")
 106 #endif
 107
 108 #pragma mark -
 109 #pragma mark _dispatch_preemption_yield
 110
 111 #if HAVE_MACH
 112 #if defined(SWITCH_OPTION_OSLOCK_DEPRESS) && !(TARGET_IPHONE_SIMULATOR && \
 113                 IPHONE_SIMULATOR_HOST_MIN_VERSION_REQUIRED < 1090)
 114 #define DISPATCH_YIELD_THREAD_SWITCH_OPTION SWITCH_OPTION_OSLOCK_DEPRESS
 115 #else
 116 #define DISPATCH_YIELD_THREAD_SWITCH_OPTION SWITCH_OPTION_DEPRESS
 117 #endif
 118 #define _dispatch_preemption_yield(n) _dispatch_thread_switch(MACH_PORT_NULL, \
 119                 DISPATCH_YIELD_THREAD_SWITCH_OPTION, (mach_msg_timeout_t)(n))
 120 #else
 121 #define _dispatch_preemption_yield(n) pthread_yield_np()
 122 #endif // HAVE_MACH
 123
 124 #pragma mark -
 125 #pragma mark _dispatch_contention_usleep
 126
 127 #ifndef DISPATCH_CONTENTION_USLEEP_START
 128 #define DISPATCH_CONTENTION_USLEEP_START 500
 129 #endif
 130 #ifndef DISPATCH_CONTENTION_USLEEP_MAX
 131 #define DISPATCH_CONTENTION_USLEEP_MAX 100000
 132 #endif
 133
 134 #if HAVE_MACH
 135 #if defined(SWITCH_OPTION_DISPATCH_CONTENTION) && !(TARGET_IPHONE_SIMULATOR && \
 136                 IPHONE_SIMULATOR_HOST_MIN_VERSION_REQUIRED < 1090)
 137 #define _dispatch_contention_usleep(u) _dispatch_thread_switch(MACH_PORT_NULL, \
 138                 SWITCH_OPTION_DISPATCH_CONTENTION, (u))
 139 #else
 140 #define _dispatch_contention_usleep(u) _dispatch_thread_switch(MACH_PORT_NULL, \
 141                 SWITCH_OPTION_WAIT, (((u)-1)/1000)+1)
 142 #endif
 143 #else
 144 #define _dispatch_contention_usleep(u) usleep((u))
 145 #endif // HAVE_MACH
 146
 147 #pragma mark -
 148 #pragma mark _dispatch_thread_switch
 149
 150 #if HAVE_MACH
 151 #define _dispatch_thread_switch(thread_name, option, option_time) \
 152                 thread_switch((thread_name), (option), (option_time))
 153
 154 #endif // HAVE_MACH
 155
 156 #endif // __DISPATCH_SHIMS_YIELD__