1 /*
2 * Copyright © 2015 Intel
3 *
4 * Permission is hereby granted, free of charge, to any person obtaining a
5 * copy of this software and associated documentation files (the "Software"),
6 * to deal in the Software without restriction, including without limitation
7 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
8 * and/or sell copies of the Software, and to permit persons to whom the
9 * Software is furnished to do so, subject to the following conditions:
10 *
11 * The above copyright notice and this permission notice (including the next
12 * paragraph) shall be included in all copies or substantial portions of the
13 * Software.
14 *
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
18 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
20 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
21 * IN THE SOFTWARE.
22 */
23
24 #ifndef _SIMPLE_MTX_H
25 #define _SIMPLE_MTX_H
26
27 #include "util/futex.h"
28 #include "util/macros.h"
29
30 #include "c11/threads.h"
31
32 #if UTIL_FUTEX_SUPPORTED
33
34 #if defined(HAVE_VALGRIND) && !defined(NDEBUG)
35 # include <valgrind.h>
36 # include <helgrind.h>
37 # define HG(x) x
38 #else
39 # define HG(x)
40 #endif
41
42 /* mtx_t - Fast, simple mutex
43 *
44 * While modern pthread mutexes are very fast (implemented using futex), they
45 * still incur a call to an external DSO and overhead of the generality and
46 * features of pthread mutexes. Most mutexes in mesa only needs lock/unlock,
47 * and the idea here is that we can inline the atomic operation and make the
48 * fast case just two intructions. Mutexes are subtle and finicky to
49 * implement, so we carefully copy the implementation from Ulrich Dreppers
50 * well-written and well-reviewed paper:
51 *
52 * "Futexes Are Tricky"
53 * http://www.akkadia.org/drepper/futex.pdf
54 *
55 * We implement "mutex3", which gives us a mutex that has no syscalls on
56 * uncontended lock or unlock. Further, the uncontended case boils down to a
57 * locked cmpxchg and an untaken branch, the uncontended unlock is just a
58 * locked decr and an untaken branch. We use __builtin_expect() to indicate
59 * that contention is unlikely so that gcc will put the contention code out of
60 * the main code flow.
61 *
62 * A fast mutex only supports lock/unlock, can't be recursive or used with
63 * condition variables.
64 */
65
66 typedef struct {
67 uint32_t val;
68 } simple_mtx_t;
69
70 #define _SIMPLE_MTX_INITIALIZER_NP { 0 }
71
72 #define _SIMPLE_MTX_INVALID_VALUE 0xd0d0d0d0
73
74 static inline void
simple_mtx_init(simple_mtx_t * mtx,ASSERTED int type)75 simple_mtx_init(simple_mtx_t *mtx, ASSERTED int type)
76 {
77 assert(type == mtx_plain);
78
79 mtx->val = 0;
80
81 HG(ANNOTATE_RWLOCK_CREATE(mtx));
82 }
83
84 static inline void
simple_mtx_destroy(ASSERTED simple_mtx_t * mtx)85 simple_mtx_destroy(ASSERTED simple_mtx_t *mtx)
86 {
87 HG(ANNOTATE_RWLOCK_DESTROY(mtx));
88 #ifndef NDEBUG
89 mtx->val = _SIMPLE_MTX_INVALID_VALUE;
90 #endif
91 }
92
93 static inline void
simple_mtx_lock(simple_mtx_t * mtx)94 simple_mtx_lock(simple_mtx_t *mtx)
95 {
96 uint32_t c;
97
98 c = __sync_val_compare_and_swap(&mtx->val, 0, 1);
99
100 assert(c != _SIMPLE_MTX_INVALID_VALUE);
101
102 if (__builtin_expect(c != 0, 0)) {
103 if (c != 2)
104 c = __sync_lock_test_and_set(&mtx->val, 2);
105 while (c != 0) {
106 futex_wait(&mtx->val, 2, NULL);
107 c = __sync_lock_test_and_set(&mtx->val, 2);
108 }
109 }
110
111 HG(ANNOTATE_RWLOCK_ACQUIRED(mtx, 1));
112 }
113
114 static inline void
simple_mtx_unlock(simple_mtx_t * mtx)115 simple_mtx_unlock(simple_mtx_t *mtx)
116 {
117 uint32_t c;
118
119 HG(ANNOTATE_RWLOCK_RELEASED(mtx, 1));
120
121 c = __sync_fetch_and_sub(&mtx->val, 1);
122
123 assert(c != _SIMPLE_MTX_INVALID_VALUE);
124
125 if (__builtin_expect(c != 1, 0)) {
126 mtx->val = 0;
127 futex_wake(&mtx->val, 1);
128 }
129 }
130
131 static inline void
simple_mtx_assert_locked(simple_mtx_t * mtx)132 simple_mtx_assert_locked(simple_mtx_t *mtx)
133 {
134 assert(mtx->val);
135 }
136
137 #else
138
139 typedef mtx_t simple_mtx_t;
140
141 #define _SIMPLE_MTX_INITIALIZER_NP _MTX_INITIALIZER_NP
142
143 static inline void
simple_mtx_init(simple_mtx_t * mtx,int type)144 simple_mtx_init(simple_mtx_t *mtx, int type)
145 {
146 mtx_init(mtx, type);
147 }
148
149 static inline void
simple_mtx_destroy(simple_mtx_t * mtx)150 simple_mtx_destroy(simple_mtx_t *mtx)
151 {
152 mtx_destroy(mtx);
153 }
154
155 static inline void
simple_mtx_lock(simple_mtx_t * mtx)156 simple_mtx_lock(simple_mtx_t *mtx)
157 {
158 mtx_lock(mtx);
159 }
160
161 static inline void
simple_mtx_unlock(simple_mtx_t * mtx)162 simple_mtx_unlock(simple_mtx_t *mtx)
163 {
164 mtx_unlock(mtx);
165 }
166
167 static inline void
simple_mtx_assert_locked(simple_mtx_t * mtx)168 simple_mtx_assert_locked(simple_mtx_t *mtx)
169 {
170 #ifdef DEBUG
171 /* NOTE: this would not work for recursive mutexes, but
172 * mtx_t doesn't support those
173 */
174 int ret = mtx_trylock(mtx);
175 assert(ret == thrd_busy);
176 if (ret == thrd_success)
177 mtx_unlock(mtx);
178 #else
179 (void)mtx;
180 #endif
181 }
182
183 #endif
184
185 #endif
186