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1 /* spin_mutex.c -*-C-*-
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2 *
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3 *************************************************************************
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4 *
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5 * Copyright (C) 2009-2016, Intel Corporation
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6 * All rights reserved.
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7 *
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8 * Redistribution and use in source and binary forms, with or without
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9 * modification, are permitted provided that the following conditions
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10 * are met:
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11 *
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12 * * Redistributions of source code must retain the above copyright
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13 * notice, this list of conditions and the following disclaimer.
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14 * * Redistributions in binary form must reproduce the above copyright
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15 * notice, this list of conditions and the following disclaimer in
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16 * the documentation and/or other materials provided with the
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17 * distribution.
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18 * * Neither the name of Intel Corporation nor the names of its
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19 * contributors may be used to endorse or promote products derived
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20 * from this software without specific prior written permission.
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21 *
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22 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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23 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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24 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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25 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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26 * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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27 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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28 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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29 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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30 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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31 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
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32 * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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33 * POSSIBILITY OF SUCH DAMAGE.
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34 *
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35 * *********************************************************************
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36 *
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37 * PLEASE NOTE: This file is a downstream copy of a file mainitained in
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38 * a repository at cilkplus.org. Changes made to this file that are not
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39 * submitted through the contribution process detailed at
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40 * http://www.cilkplus.org/submit-cilk-contribution will be lost the next
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41 * time that a new version is released. Changes only submitted to the
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42 * GNU compiler collection or posted to the git repository at
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43 * https://bitbucket.org/intelcilkruntime/intel-cilk-runtime.git are
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44 * not tracked.
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45 *
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46 * We welcome your contributions to this open source project. Thank you
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47 * for your assistance in helping us improve Cilk Plus.
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48 **************************************************************************/
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49
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50 #include "spin_mutex.h"
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51 #include "bug.h"
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52 #include "os.h"
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53 #include "stats.h"
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54
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55 // TBD (11/30/12): We should be doing a conditional test-xchg instead
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56 // of an unconditional xchg operation for the spin mutex.
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57
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58 /* m->lock == 1 means that mutex M is locked */
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59 #define TRY_ACQUIRE(m) (__cilkrts_xchg(&(m)->lock, 1) == 0)
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60
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61 /* ICC 11.1+ understands release semantics and generates an
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62 ordinary store with a software memory barrier. */
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63 #if __ICC >= 1110
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64 #define RELEASE(m) __sync_lock_release(&(m)->lock)
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65 #else
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66 #define RELEASE(m) __cilkrts_xchg(&(m)->lock, 0)
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67 #endif
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68
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69
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70 spin_mutex* spin_mutex_create()
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71 {
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72 spin_mutex* mutex = (spin_mutex*)__cilkrts_malloc(sizeof(spin_mutex));
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73 spin_mutex_init(mutex);
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74 return mutex;
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75 }
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76
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77 void spin_mutex_init(struct spin_mutex *m)
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78 {
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79 // Use a simple assignment so Inspector doesn't bug us about the
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80 // interlocked exchange doing a read of an uninitialized variable.
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81 // By definition there can't be a race when we're initializing the
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82 // lock...
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83 m->lock = 0;
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84 }
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85
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86 void spin_mutex_lock(struct spin_mutex *m)
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87 {
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88 int count;
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89 const int maxspin = 1000; /* SWAG */
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90 if (!TRY_ACQUIRE(m)) {
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91 count = 0;
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92 do {
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93 do {
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94 __cilkrts_short_pause();
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95 if (++count >= maxspin) {
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96 /* let the OS reschedule every once in a while */
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97 __cilkrts_yield();
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98 count = 0;
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99 }
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100 } while (m->lock != 0);
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101 } while (!TRY_ACQUIRE(m));
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102 }
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103 }
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104
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105 int spin_mutex_trylock(struct spin_mutex *m)
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106 {
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107 return TRY_ACQUIRE(m);
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108 }
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109
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110 void spin_mutex_unlock(struct spin_mutex *m)
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111 {
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112 RELEASE(m);
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113 }
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114
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115 void spin_mutex_destroy(struct spin_mutex *m)
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116 {
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117 __cilkrts_free(m);
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118 }
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119
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120 /* End spin_mutex.c */
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