libcilkrts/runtime/spin_mutex.c

   1 /* spin_mutex.c                  -*-C-*-
   2  *
   3  *************************************************************************
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   5  *  Copyright (C) 2009-2016, Intel Corporation
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  48  **************************************************************************/
  49
  50 #include "spin_mutex.h"
  51 #include "bug.h"
  52 #include "os.h"
  53 #include "stats.h"
  54
  55 // TBD (11/30/12): We should be doing a conditional test-xchg instead
  56 // of an unconditional xchg operation for the spin mutex.
  57
  58 /* m->lock == 1 means that mutex M is locked */
  59 #define TRY_ACQUIRE(m) (__cilkrts_xchg(&(m)->lock, 1) == 0)
  60
  61 /* ICC 11.1+ understands release semantics and generates an
  62    ordinary store with a software memory barrier. */
  63 #if __ICC >= 1110
  64 #define RELEASE(m) __sync_lock_release(&(m)->lock)
  65 #else
  66 #define RELEASE(m) __cilkrts_xchg(&(m)->lock, 0)
  67 #endif
  68
  69
  70 spin_mutex* spin_mutex_create()
  71 {
  72     spin_mutex* mutex = (spin_mutex*)__cilkrts_malloc(sizeof(spin_mutex));
  73     spin_mutex_init(mutex);
  74     return mutex;
  75 }
  76
  77 void spin_mutex_init(struct spin_mutex *m)
  78 {
  79     // Use a simple assignment so Inspector doesn't bug us about the
  80     // interlocked exchange doing a read of an uninitialized variable.
  81     // By definition there can't be a race when we're initializing the
  82     // lock...
  83     m->lock = 0;
  84 }
  85
  86 void spin_mutex_lock(struct spin_mutex *m)
  87 {
  88     int count;
  89     const int maxspin = 1000; /* SWAG */
  90     if (!TRY_ACQUIRE(m)) {
  91         count = 0;
  92         do {
  93             do {
  94                 __cilkrts_short_pause();
  95                 if (++count >= maxspin) {
  96                     /* let the OS reschedule every once in a while */
  97                     __cilkrts_yield();
  98                     count = 0;
  99                 }
 100             } while (m->lock != 0);
 101         } while (!TRY_ACQUIRE(m));
 102     }
 103 }
 104
 105 int spin_mutex_trylock(struct spin_mutex *m)
 106 {
 107     return TRY_ACQUIRE(m);
 108 }
 109
 110 void spin_mutex_unlock(struct spin_mutex *m)
 111 {
 112     RELEASE(m);
 113 }
 114
 115 void spin_mutex_destroy(struct spin_mutex *m)
 116 {
 117     __cilkrts_free(m);
 118 }
 119
 120 /* End spin_mutex.c */