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1 /* | 1 /* |
2 * Copyright 2013 Google Inc. | 2 * Copyright 2013 Google Inc. |
3 * | 3 * |
4 * Use of this source code is governed by a BSD-style license that can be | 4 * Use of this source code is governed by a BSD-style license that can be |
5 * found in the LICENSE file. | 5 * found in the LICENSE file. |
6 */ | 6 */ |
7 | 7 |
8 #ifndef SkOnce_DEFINED | 8 #ifndef SkOnce_DEFINED |
9 #define SkOnce_DEFINED | 9 #define SkOnce_DEFINED |
10 | 10 |
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21 // SK_DECLARE_STATIC_ONCE(once); | 21 // SK_DECLARE_STATIC_ONCE(once); |
22 // SkOnce(&once, set_up_my_singleton, &singleton); | 22 // SkOnce(&once, set_up_my_singleton, &singleton); |
23 // SkASSERT(NULL != singleton); | 23 // SkASSERT(NULL != singleton); |
24 // return *singleton; | 24 // return *singleton; |
25 // } | 25 // } |
26 // | 26 // |
27 // OnceTest.cpp also should serve as a few other simple examples. | 27 // OnceTest.cpp also should serve as a few other simple examples. |
28 // | 28 // |
29 // You may optionally pass SkOnce a second function to be called at exit for cle
anup. | 29 // You may optionally pass SkOnce a second function to be called at exit for cle
anup. |
30 | 30 |
| 31 #include "SkDynamicAnnotations.h" |
31 #include "SkThread.h" | 32 #include "SkThread.h" |
32 #include "SkTypes.h" | 33 #include "SkTypes.h" |
33 | 34 |
34 #define SK_ONCE_INIT { false, { 0, SkDEBUGCODE(0) } } | 35 #define SK_ONCE_INIT { false, { 0, SkDEBUGCODE(0) } } |
35 #define SK_DECLARE_STATIC_ONCE(name) static SkOnceFlag name = SK_ONCE_INIT | 36 #define SK_DECLARE_STATIC_ONCE(name) static SkOnceFlag name = SK_ONCE_INIT |
36 | 37 |
37 struct SkOnceFlag; // If manually created, initialize with SkOnceFlag once = SK
_ONCE_INIT | 38 struct SkOnceFlag; // If manually created, initialize with SkOnceFlag once = SK
_ONCE_INIT |
38 | 39 |
39 template <typename Func, typename Arg> | 40 template <typename Func, typename Arg> |
40 inline void SkOnce(SkOnceFlag* once, Func f, Arg arg, void(*atExit)() = NULL); | 41 inline void SkOnce(SkOnceFlag* once, Func f, Arg arg, void(*atExit)() = NULL); |
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108 // In version control terms this is like saying, "check in the work up | 109 // In version control terms this is like saying, "check in the work up |
109 // to and including f(arg), then check in *done=true as a subsequent cha
nge". | 110 // to and including f(arg), then check in *done=true as a subsequent cha
nge". |
110 // | 111 // |
111 // We'll use this in the fast path to make sure f(arg)'s effects are | 112 // We'll use this in the fast path to make sure f(arg)'s effects are |
112 // observable whenever we observe *done == true. | 113 // observable whenever we observe *done == true. |
113 release_barrier(); | 114 release_barrier(); |
114 once->done = true; | 115 once->done = true; |
115 } | 116 } |
116 } | 117 } |
117 | 118 |
118 // We nabbed this code from the dynamic_annotations library, and in their honor | |
119 // we check the same define. If you find yourself wanting more than just | |
120 // SK_ANNOTATE_BENIGN_RACE, it might make sense to pull that in as a dependency | |
121 // rather than continue to reproduce it here. | |
122 | |
123 #if DYNAMIC_ANNOTATIONS_ENABLED | |
124 // TSAN provides this hook to supress a known-safe apparent race. | |
125 extern "C" { | |
126 void AnnotateBenignRace(const char* file, int line, const volatile void* mem, co
nst char* desc); | |
127 } | |
128 #define SK_ANNOTATE_BENIGN_RACE(mem, desc) AnnotateBenignRace(__FILE__, __LINE__
, mem, desc) | |
129 #else | |
130 #define SK_ANNOTATE_BENIGN_RACE(mem, desc) | |
131 #endif | |
132 | |
133 // This is our fast path, called all the time. We do really want it to be inlin
ed. | 119 // This is our fast path, called all the time. We do really want it to be inlin
ed. |
134 template <typename Func, typename Arg> | 120 template <typename Func, typename Arg> |
135 inline void SkOnce(SkOnceFlag* once, Func f, Arg arg, void(*atExit)()) { | 121 inline void SkOnce(SkOnceFlag* once, Func f, Arg arg, void(*atExit)()) { |
136 SK_ANNOTATE_BENIGN_RACE(&(once->done), "Don't worry TSAN, we're sure this is
safe."); | 122 if (!SK_ANNOTATE_UNPROTECTED_READ(once->done)) { |
137 if (!once->done) { | |
138 sk_once_slow(once, f, arg, atExit); | 123 sk_once_slow(once, f, arg, atExit); |
139 } | 124 } |
140 // Also known as a load-load/load-store barrier, this acquire barrier makes | 125 // Also known as a load-load/load-store barrier, this acquire barrier makes |
141 // sure that anything we read from memory---in particular, memory written by | 126 // sure that anything we read from memory---in particular, memory written by |
142 // calling f(arg)---is at least as current as the value we read from once->d
one. | 127 // calling f(arg)---is at least as current as the value we read from once->d
one. |
143 // | 128 // |
144 // In version control terms, this is a lot like saying "sync up to the | 129 // In version control terms, this is a lot like saying "sync up to the |
145 // commit where we wrote once->done = true". | 130 // commit where we wrote once->done = true". |
146 // | 131 // |
147 // The release barrier in sk_once_slow guaranteed that once->done = true | 132 // The release barrier in sk_once_slow guaranteed that once->done = true |
148 // happens after f(arg), so by syncing to once->done = true here we're | 133 // happens after f(arg), so by syncing to once->done = true here we're |
149 // forcing ourselves to also wait until the effects of f(arg) are readble. | 134 // forcing ourselves to also wait until the effects of f(arg) are readble. |
150 acquire_barrier(); | 135 acquire_barrier(); |
151 } | 136 } |
152 | 137 |
153 #undef SK_ANNOTATE_BENIGN_RACE | 138 #undef SK_ANNOTATE_BENIGN_RACE |
154 | 139 |
155 #endif // SkOnce_DEFINED | 140 #endif // SkOnce_DEFINED |
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