libcilkrts/runtime/spin_mutex.c

   1 /* spin_mutex.c                  -*-C-*-
   2  *
   3  *************************************************************************
   4  *
   5  *  @copyright
   6  *  Copyright (C) 2009-2013, Intel Corporation
   7  *  All rights reserved.
   8  *
   9  *  @copyright
  10  *  Redistribution and use in source and binary forms, with or without
  11  *  modification, are permitted provided that the following conditions
  12  *  are met:
  13  *
  14  *    * Redistributions of source code must retain the above copyright
  15  *      notice, this list of conditions and the following disclaimer.
  16  *    * Redistributions in binary form must reproduce the above copyright
  17  *      notice, this list of conditions and the following disclaimer in
  18  *      the documentation and/or other materials provided with the
  19  *      distribution.
  20  *    * Neither the name of Intel Corporation nor the names of its
  21  *      contributors may be used to endorse or promote products derived
  22  *      from this software without specific prior written permission.
  23  *
  24  *  @copyright
  25  *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  26  *  "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  27  *  LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  28  *  A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  29  *  HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  30  *  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
  31  *  BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
  32  *  OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
  33  *  AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  34  *  LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
  35  *  WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  36  *  POSSIBILITY OF SUCH DAMAGE.
  37  **************************************************************************/
  38
  39 #include "spin_mutex.h"
  40 #include "bug.h"
  41 #include "os.h"
  42 #include "stats.h"
  43
  44 // TBD (11/30/12): We should be doing a conditional test-xchg instead
  45 // of an unconditional xchg operation for the spin mutex.
  46
  47 /* m->lock == 1 means that mutex M is locked */
  48 #define TRY_ACQUIRE(m) (__cilkrts_xchg(&(m)->lock, 1) == 0)
  49
  50 /* ICC 11.1+ understands release semantics and generates an
  51    ordinary store with a software memory barrier. */
  52 #if __ICC >= 1110
  53 #define RELEASE(m) __sync_lock_release(&(m)->lock)
  54 #else
  55 #define RELEASE(m) __cilkrts_xchg(&(m)->lock, 0)
  56 #endif
  57
  58
  59 spin_mutex* spin_mutex_create()
  60 {
  61     spin_mutex* mutex = (spin_mutex*)__cilkrts_malloc(sizeof(spin_mutex));
  62     spin_mutex_init(mutex);
  63     return mutex;
  64 }
  65
  66 void spin_mutex_init(struct spin_mutex *m)
  67 {
  68     // Use a simple assignment so Inspector doesn't bug us about the
  69     // interlocked exchange doing a read of an uninitialized variable.
  70     // By definition there can't be a race when we're initializing the
  71     // lock...
  72     m->lock = 0;
  73 }
  74
  75 void spin_mutex_lock(struct spin_mutex *m)
  76 {
  77     int count;
  78     const int maxspin = 1000; /* SWAG */
  79     if (!TRY_ACQUIRE(m)) {
  80         count = 0;
  81         do {
  82             do {
  83                 __cilkrts_short_pause();
  84                 if (++count >= maxspin) {
  85                     /* let the OS reschedule every once in a while */
  86                     __cilkrts_yield();
  87                     count = 0;
  88                 }
  89             } while (m->lock != 0);
  90         } while (!TRY_ACQUIRE(m));
  91     }
  92 }
  93
  94 int spin_mutex_trylock(struct spin_mutex *m)
  95 {
  96     return TRY_ACQUIRE(m);
  97 }
  98
  99 void spin_mutex_unlock(struct spin_mutex *m)
 100 {
 101     RELEASE(m);
 102 }
 103
 104 void spin_mutex_destroy(struct spin_mutex *m)
 105 {
 106     __cilkrts_free(m);
 107 }
 108
 109 /* End spin_mutex.c */