internal/os/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 libplatform
  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 __OS_YIELD__
  28 #define __OS_YIELD__
  29
  30 #include <TargetConditionals.h>
  31
  32 #pragma mark -
  33 #pragma mark _os_wait_until
  34
  35 #if OS_ATOMIC_UP
  36 #define _os_wait_until(c) do { \
  37                 int _spins = 0; \
  38                 while (unlikely(!(c))) { \
  39                         _spins++; \
  40                         _os_preemption_yield(_spins); \
  41                 } } while (0)
  42 #elif TARGET_OS_EMBEDDED
  43 // <rdar://problem/15508918>
  44 #ifndef OS_WAIT_SPINS
  45 #define OS_WAIT_SPINS 1024
  46 #endif
  47 #define _os_wait_until(c) do { \
  48                 int _spins = -(OS_WAIT_SPINS); \
  49                 while (unlikely(!(c))) { \
  50                         if (unlikely(_spins++ >= 0)) { \
  51                                 _os_preemption_yield(_spins); \
  52                         } else { \
  53                                 os_hardware_pause(); \
  54                         } \
  55                 } } while (0)
  56 #else
  57 #define _os_wait_until(c) do { \
  58                 while (!(c)) { \
  59                         os_hardware_pause(); \
  60                 } } while (0)
  61 #endif
  62
  63 #pragma mark -
  64 #pragma mark os_hardware_pause
  65
  66 #if defined(__x86_64__) || defined(__i386__)
  67 #define os_hardware_pause() __asm__("pause")
  68 #elif (defined(__arm__) && defined(_ARM_ARCH_7) && defined(__thumb__)) || \
  69                 defined(__arm64__)
  70 #define os_hardware_pause() __asm__("yield")
  71 #define os_hardware_wfe()   __asm__("wfe")
  72 #else
  73 #define os_hardware_pause() __asm__("")
  74 #endif
  75
  76 #pragma mark -
  77 #pragma mark _os_preemption_yield
  78
  79 #if defined(SWITCH_OPTION_OSLOCK_DEPRESS) && !(TARGET_IPHONE_SIMULATOR && \
  80                 IPHONE_SIMULATOR_HOST_MIN_VERSION_REQUIRED < 1090)
  81 #define OS_YIELD_THREAD_SWITCH_OPTION SWITCH_OPTION_OSLOCK_DEPRESS
  82 #else
  83 #define OS_YIELD_THREAD_SWITCH_OPTION SWITCH_OPTION_DEPRESS
  84 #endif
  85 #define _os_preemption_yield(n) thread_switch(MACH_PORT_NULL, \
  86                 OS_YIELD_THREAD_SWITCH_OPTION, (mach_msg_timeout_t)(n))
  87
  88 #endif // __OS_YIELD__