lib/pthread-spin.c

   1 /* POSIX spin locks.
   2    Copyright (C) 2010-2019 Free Software Foundation, Inc.
   3
   4    This program is free software; you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 2, or (at your option)
   7    any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program; if not, see <https://www.gnu.org/licenses/>.  */
  16
  17 /* Written by Paul Eggert, 2010, and Bruno Haible <bruno@clisp.org>, 2019.  */
  18
  19 #include <config.h>
  20
  21 /* Specification.  */
  22 #include <pthread.h>
  23
  24 #if (defined _WIN32 && ! defined __CYGWIN__) && USE_WINDOWS_THREADS
  25 # include "windows-spin.h"
  26 #endif
  27
  28 #if (defined _WIN32 && ! defined __CYGWIN__) && USE_WINDOWS_THREADS
  29 /* Use Windows threads.  */
  30
  31 int
  32 pthread_spin_init (pthread_spinlock_t *lock,
  33                    int shared_across_processes _GL_UNUSED)
  34 {
  35   glwthread_spin_init (lock);
  36   return 0;
  37 }
  38
  39 int
  40 pthread_spin_lock (pthread_spinlock_t *lock)
  41 {
  42   return glwthread_spin_lock (lock);
  43 }
  44
  45 int
  46 pthread_spin_trylock (pthread_spinlock_t *lock)
  47 {
  48   return glwthread_spin_trylock (lock);
  49 }
  50
  51 int
  52 pthread_spin_unlock (pthread_spinlock_t *lock)
  53 {
  54   return glwthread_spin_unlock (lock);
  55 }
  56
  57 int
  58 pthread_spin_destroy (pthread_spinlock_t *lock)
  59 {
  60   return glwthread_spin_destroy (lock);
  61 }
  62
  63 #elif HAVE_PTHREAD_H
  64 /* Provide workarounds for POSIX threads.  */
  65
  66 /* We don't use the C11 <stdatomic.h> (available in GCC >= 4.9) because it would
  67    require to link with -latomic.  */
  68
  69 # if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 7)
  70 /* Use GCC built-ins (available in GCC >= 4.7) that operate on the first byte
  71    of the lock.
  72    Documentation:
  73    <https://gcc.gnu.org/onlinedocs/gcc-4.7.0/gcc/_005f_005fatomic-Builtins.html>  */
  74
  75 int
  76 pthread_spin_init (pthread_spinlock_t *lock,
  77                    int shared_across_processes _GL_UNUSED)
  78 {
  79   __atomic_clear (lock, __ATOMIC_SEQ_CST);
  80   return 0;
  81 }
  82
  83 int
  84 pthread_spin_lock (pthread_spinlock_t *lock)
  85 {
  86   while (__atomic_test_and_set (lock, __ATOMIC_SEQ_CST))
  87     ;
  88   return 0;
  89 }
  90
  91 int
  92 pthread_spin_trylock (pthread_spinlock_t *lock)
  93 {
  94   if (__atomic_test_and_set (lock, __ATOMIC_SEQ_CST))
  95     return EBUSY;
  96   return 0;
  97 }
  98
  99 int
 100 pthread_spin_unlock (pthread_spinlock_t *lock)
 101 {
 102   __atomic_clear (lock, __ATOMIC_SEQ_CST);
 103   return 0;
 104 }
 105
 106 int
 107 pthread_spin_destroy (pthread_spinlock_t *lock)
 108 {
 109   return 0;
 110 }
 111
 112 # else
 113 /* Emulate a spin lock through a mutex.  */
 114
 115 int
 116 pthread_spin_init (pthread_spinlock_t *lock,
 117                    int shared_across_processes _GL_UNUSED)
 118 {
 119   return pthread_mutex_init (lock, NULL);
 120 }
 121
 122 int
 123 pthread_spin_lock (pthread_spinlock_t *lock)
 124 {
 125   return pthread_mutex_lock (lock);
 126 }
 127
 128 int
 129 pthread_spin_trylock (pthread_spinlock_t *lock)
 130 {
 131   return pthread_mutex_trylock (lock);
 132 }
 133
 134 int
 135 pthread_spin_unlock (pthread_spinlock_t *lock)
 136 {
 137   return pthread_mutex_unlock (lock);
 138 }
 139
 140 int
 141 pthread_spin_destroy (pthread_spinlock_t *lock)
 142 {
 143   return pthread_mutex_destroy (lock);
 144 }
 145
 146 # endif
 147
 148 #else
 149 /* Provide a dummy implementation for single-threaded applications.  */
 150
 151 int
 152 pthread_spin_init (pthread_spinlock_t *lock _GL_UNUSED,
 153                    int shared_across_processes _GL_UNUSED)
 154 {
 155   return 0;
 156 }
 157
 158 int
 159 pthread_spin_lock (pthread_spinlock_t *lock _GL_UNUSED)
 160 {
 161   return 0;
 162 }
 163
 164 int
 165 pthread_spin_trylock (pthread_spinlock_t *lock _GL_UNUSED)
 166 {
 167   return 0;
 168 }
 169
 170 int
 171 pthread_spin_unlock (pthread_spinlock_t *lock _GL_UNUSED)
 172 {
 173   return 0;
 174 }
 175
 176 int
 177 pthread_spin_destroy (pthread_spinlock_t *lock _GL_UNUSED)
 178 {
 179   return 0;
 180 }
 181
 182 #endif