linuxthreads/spinlock.h

   1 /* Linuxthreads - a simple clone()-based implementation of Posix        */
   2 /* threads for Linux.                                                   */
   3 /* Copyright (C) 1998 Xavier Leroy (Xavier.Leroy@inria.fr)              */
   4 /*                                                                      */
   5 /* This program is free software; you can redistribute it and/or        */
   6 /* modify it under the terms of the GNU Library General Public License  */
   7 /* as published by the Free Software Foundation; either version 2       */
   8 /* of the License, or (at your option) any later version.               */
   9 /*                                                                      */
  10 /* This program is distributed in the hope that it will be useful,      */
  11 /* but WITHOUT ANY WARRANTY; without even the implied warranty of       */
  12 /* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the        */
  13 /* GNU Library General Public License for more details.                 */
  14
  15 #include <bits/initspin.h>
  16
  17
  18 /* There are 2 compare and swap synchronization primitives with
  19    different semantics:
  20
  21         1. compare_and_swap, which has acquire semantics (i.e. it
  22         completes befor subsequent writes.)
  23         2. compare_and_swap_with_release_semantics, which has release
  24         semantics (it completes after previous writes.)
  25
  26    For those platforms on which they are the same. HAS_COMPARE_AND_SWAP
  27    should be defined. For those platforms on which they are different,
  28    HAS_COMPARE_AND_SWAP_WITH_RELEASE_SEMANTICS has to be defined.  */
  29
  30 #ifndef HAS_COMPARE_AND_SWAP
  31 #ifdef HAS_COMPARE_AND_SWAP_WITH_RELEASE_SEMANTICS
  32 #define HAS_COMPARE_AND_SWAP
  33 #endif
  34 #endif
  35
  36 #if defined(TEST_FOR_COMPARE_AND_SWAP)
  37
  38 extern int __pthread_has_cas;
  39 extern int __pthread_compare_and_swap(long * ptr, long oldval, long newval,
  40                                       int * spinlock);
  41
  42 static inline int compare_and_swap(long * ptr, long oldval, long newval,
  43                                    int * spinlock)
  44 {
  45   if (__builtin_expect (__pthread_has_cas, 1))
  46     return __compare_and_swap(ptr, oldval, newval);
  47   else
  48     return __pthread_compare_and_swap(ptr, oldval, newval, spinlock);
  49 }
  50
  51 #elif defined(HAS_COMPARE_AND_SWAP)
  52
  53 #ifdef IMPLEMENT_TAS_WITH_CAS
  54 #define testandset(p) !__compare_and_swap((long int *) p, 0, 1)
  55 #endif
  56
  57 #ifdef HAS_COMPARE_AND_SWAP_WITH_RELEASE_SEMANTICS
  58
  59 static inline int
  60 compare_and_swap_with_release_semantics (long * ptr, long oldval,
  61                                          long newval, int * spinlock)
  62 {
  63   return __compare_and_swap_with_release_semantics (ptr, oldval,
  64                                                     newval);
  65 }
  66
  67 #endif
  68
  69 static inline int compare_and_swap(long * ptr, long oldval, long newval,
  70                                    int * spinlock)
  71 {
  72   return __compare_and_swap(ptr, oldval, newval);
  73 }
  74
  75 #else
  76
  77 extern int __pthread_compare_and_swap(long * ptr, long oldval, long newval,
  78                                       int * spinlock);
  79
  80 static inline int compare_and_swap(long * ptr, long oldval, long newval,
  81                                    int * spinlock)
  82 {
  83   return __pthread_compare_and_swap(ptr, oldval, newval, spinlock);
  84 }
  85
  86 #endif
  87
  88 #ifndef HAS_COMPARE_AND_SWAP_WITH_RELEASE_SEMANTICS
  89 #define compare_and_swap_with_release_semantics compare_and_swap
  90 #define __compare_and_swap_with_release_semantics __compare_and_swap
  91 #endif
  92
  93 /* Internal locks */
  94
  95 extern void internal_function __pthread_lock(struct _pthread_fastlock * lock,
  96                                              pthread_descr self);
  97 extern int __pthread_unlock(struct _pthread_fastlock *lock);
  98
  99 static inline void __pthread_init_lock(struct _pthread_fastlock * lock)
 100 {
 101   lock->__status = 0;
 102   lock->__spinlock = __LT_SPINLOCK_INIT;
 103 }
 104
 105 static inline int __pthread_trylock (struct _pthread_fastlock * lock)
 106 {
 107 #if defined TEST_FOR_COMPARE_AND_SWAP
 108   if (!__pthread_has_cas)
 109 #endif
 110 #if !defined HAS_COMPARE_AND_SWAP || defined TEST_FOR_COMPARE_AND_SWAP
 111   {
 112     return (testandset(&lock->__spinlock) ? EBUSY : 0);
 113   }
 114 #endif
 115
 116 #if defined HAS_COMPARE_AND_SWAP
 117   do {
 118     if (lock->__status != 0) return EBUSY;
 119   } while(! __compare_and_swap(&lock->__status, 0, 1));
 120   return 0;
 121 #endif
 122 }
 123
 124 /* Variation of internal lock used for pthread_mutex_t, supporting
 125    timed-out waits.  Warning: do not mix these operations with the above ones
 126    over the same lock object! */
 127
 128 extern void __pthread_alt_lock(struct _pthread_fastlock * lock,
 129                                pthread_descr self);
 130
 131 extern int __pthread_alt_timedlock(struct _pthread_fastlock * lock,
 132                                pthread_descr self, const struct timespec *abstime);
 133
 134 extern void __pthread_alt_unlock(struct _pthread_fastlock *lock);
 135
 136 static inline void __pthread_alt_init_lock(struct _pthread_fastlock * lock)
 137 {
 138   lock->__status = 0;
 139   lock->__spinlock = __LT_SPINLOCK_INIT;
 140 }
 141
 142 static inline int __pthread_alt_trylock (struct _pthread_fastlock * lock)
 143 {
 144 #if defined TEST_FOR_COMPARE_AND_SWAP
 145   if (!__pthread_has_cas)
 146 #endif
 147 #if !defined HAS_COMPARE_AND_SWAP || defined TEST_FOR_COMPARE_AND_SWAP
 148   {
 149     int res = EBUSY;
 150
 151     if (testandset(&lock->__spinlock) == 0)
 152       {
 153         if (lock->__status == 0)
 154           {
 155             lock->__status = 1;
 156             WRITE_MEMORY_BARRIER();
 157             res = 0;
 158           }
 159         lock->__spinlock = __LT_SPINLOCK_INIT;
 160       }
 161     return res;
 162   }
 163 #endif
 164
 165 #if defined HAS_COMPARE_AND_SWAP
 166   do {
 167     if (lock->__status != 0) return EBUSY;
 168   } while(! compare_and_swap(&lock->__status, 0, 1, &lock->__spinlock));
 169   return 0;
 170 #endif
 171 }
 172
 173 /* Operations on pthread_atomic, which is defined in internals.h */
 174
 175 static inline long atomic_increment(struct pthread_atomic *pa)
 176 {
 177     long oldval;
 178
 179     do {
 180         oldval = pa->p_count;
 181     } while (!compare_and_swap(&pa->p_count, oldval, oldval + 1, &pa->p_spinlock));
 182
 183     return oldval;
 184 }
 185
 186
 187 static inline long atomic_decrement(struct pthread_atomic *pa)
 188 {
 189     long oldval;
 190
 191     do {
 192         oldval = pa->p_count;
 193     } while (!compare_and_swap(&pa->p_count, oldval, oldval - 1, &pa->p_spinlock));
 194
 195     return oldval;
 196 }
 197
 198
 199 static inline __attribute__((always_inline)) void
 200 __pthread_set_own_extricate_if (pthread_descr self, pthread_extricate_if *peif)
 201 {
 202   /* Only store a non-null peif if the thread has cancellation enabled.
 203      Otherwise pthread_cancel will unconditionally call the extricate handler,
 204      and restart the thread giving rise to forbidden spurious wakeups. */
 205   if (peif == NULL
 206       || THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE)
 207     {
 208       /* If we are removing the extricate interface, we need to synchronize
 209          against pthread_cancel so that it does not continue with a pointer
 210          to a deallocated pthread_extricate_if struct! The thread lock
 211          is (ab)used for this synchronization purpose. */
 212       if (peif == NULL)
 213         __pthread_lock (THREAD_GETMEM(self, p_lock), self);
 214       THREAD_SETMEM(self, p_extricate, peif);
 215       if (peif == NULL)
 216         __pthread_unlock (THREAD_GETMEM(self, p_lock));
 217     }
 218 }