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
spin_mutex_create()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
spin_mutex_init(struct spin_mutex * m)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
spin_mutex_lock(struct spin_mutex * m)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
spin_mutex_trylock(struct spin_mutex * m)94 int spin_mutex_trylock(struct spin_mutex *m)
95 {
96 return TRY_ACQUIRE(m);
97 }
98
spin_mutex_unlock(struct spin_mutex * m)99 void spin_mutex_unlock(struct spin_mutex *m)
100 {
101 RELEASE(m);
102 }
103
spin_mutex_destroy(struct spin_mutex * m)104 void spin_mutex_destroy(struct spin_mutex *m)
105 {
106 __cilkrts_free(m);
107 }
108
109 /* End spin_mutex.c */
110