libgo/runtime/thread.c

   1 // Copyright 2010 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 #include <errno.h>
   6 #include "runtime.h"
   7 #include "go-assert.h"
   8
   9 void
  10 runtime_initlock(Lock *l)
  11 {
  12         l->key = 0;
  13         if(sem_init(&l->sem, 0, 0) != 0)
  14                 runtime_throw("sem_init failed");
  15 }
  16
  17 static uint32
  18 runtime_xadd(uint32 volatile *val, int32 delta)
  19 {
  20         uint32 oval, nval;
  21
  22         for(;;){
  23                 oval = *val;
  24                 nval = oval + delta;
  25                 if(runtime_cas(val, oval, nval))
  26                         return nval;
  27         }
  28 }
  29
  30 // noinline so that runtime_lock doesn't have to split the stack.
  31 static void runtime_lock_full(Lock *l) __attribute__ ((noinline));
  32
  33 static void
  34 runtime_lock_full(Lock *l)
  35 {
  36         for(;;){
  37                 if(sem_wait(&l->sem) == 0)
  38                         return;
  39                 if(errno != EINTR)
  40                         runtime_throw("sem_wait failed");
  41         }
  42 }
  43
  44 void
  45 runtime_lock(Lock *l)
  46 {
  47         if(m != nil) {
  48                 if(m->locks < 0)
  49                         runtime_throw("lock count");
  50                 m->locks++;
  51         }
  52
  53         if(runtime_xadd(&l->key, 1) > 1)        // someone else has it; wait
  54                 runtime_lock_full(l);
  55 }
  56
  57 static void runtime_unlock_full(Lock *l) __attribute__ ((noinline));
  58
  59 static void
  60 runtime_unlock_full(Lock *l)
  61 {
  62         if(sem_post(&l->sem) != 0)
  63                 runtime_throw("sem_post failed");
  64 }
  65
  66 void
  67 runtime_unlock(Lock *l)
  68 {
  69         if(m != nil) {
  70                 m->locks--;
  71                 if(m->locks < 0)
  72                         runtime_throw("lock count");
  73         }
  74
  75         if(runtime_xadd(&l->key, -1) > 0)       // someone else is waiting
  76                 runtime_unlock_full(l);
  77 }
  78
  79 void
  80 runtime_destroylock(Lock *l)
  81 {
  82         sem_destroy(&l->sem);
  83 }
  84
  85 #ifndef HAVE_SYNC_BOOL_COMPARE_AND_SWAP_4
  86
  87 // For targets which don't have the required sync support.  Really
  88 // this should be provided by gcc itself.  FIXME.
  89
  90 static pthread_mutex_t sync_lock = PTHREAD_MUTEX_INITIALIZER;
  91
  92 _Bool
  93 __sync_bool_compare_and_swap_4(uint32*, uint32, uint32)
  94   __attribute__((visibility("hidden")));
  95
  96 _Bool
  97 __sync_bool_compare_and_swap_4(uint32* ptr, uint32 old, uint32 new)
  98 {
  99   int i;
 100   _Bool ret;
 101
 102   i = pthread_mutex_lock(&sync_lock);
 103   __go_assert(i == 0);
 104
 105   if(*ptr != old) {
 106     ret = 0;
 107   } else {
 108     *ptr = new;
 109     ret = 1;
 110   }
 111
 112   i = pthread_mutex_unlock(&sync_lock);
 113   __go_assert(i == 0);
 114
 115   return ret;
 116 }
 117
 118 #endif