1 | // Copyright 2017 The Abseil Authors. |
2 | // |
3 | // Licensed under the Apache License, Version 2.0 (the "License"); |
4 | // you may not use this file except in compliance with the License. |
5 | // You may obtain a copy of the License at |
6 | // |
7 | // https://www.apache.org/licenses/LICENSE-2.0 |
8 | // |
9 | // Unless required by applicable law or agreed to in writing, software |
10 | // distributed under the License is distributed on an "AS IS" BASIS, |
11 | // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
12 | // See the License for the specific language governing permissions and |
13 | // limitations under the License. |
14 | |
15 | #ifndef ABSL_BASE_INTERNAL_SPINLOCK_WAIT_H_ |
16 | #define ABSL_BASE_INTERNAL_SPINLOCK_WAIT_H_ |
17 | |
18 | // Operations to make atomic transitions on a word, and to allow |
19 | // waiting for those transitions to become possible. |
20 | |
21 | #include <stdint.h> |
22 | #include <atomic> |
23 | |
24 | #include "absl/base/internal/scheduling_mode.h" |
25 | |
26 | namespace absl { |
27 | ABSL_NAMESPACE_BEGIN |
28 | namespace base_internal { |
29 | |
30 | // SpinLockWait() waits until it can perform one of several transitions from |
31 | // "from" to "to". It returns when it performs a transition where done==true. |
32 | struct SpinLockWaitTransition { |
33 | uint32_t from; |
34 | uint32_t to; |
35 | bool done; |
36 | }; |
37 | |
38 | // Wait until *w can transition from trans[i].from to trans[i].to for some i |
39 | // satisfying 0<=i<n && trans[i].done, atomically make the transition, |
40 | // then return the old value of *w. Make any other atomic transitions |
41 | // where !trans[i].done, but continue waiting. |
42 | // |
43 | // Wakeups for threads blocked on SpinLockWait do not respect priorities. |
44 | uint32_t SpinLockWait(std::atomic<uint32_t> *w, int n, |
45 | const SpinLockWaitTransition trans[], |
46 | SchedulingMode scheduling_mode); |
47 | |
48 | // If possible, wake some thread that has called SpinLockDelay(w, ...). If `all` |
49 | // is true, wake all such threads. On some systems, this may be a no-op; on |
50 | // those systems, threads calling SpinLockDelay() will always wake eventually |
51 | // even if SpinLockWake() is never called. |
52 | void SpinLockWake(std::atomic<uint32_t> *w, bool all); |
53 | |
54 | // Wait for an appropriate spin delay on iteration "loop" of a |
55 | // spin loop on location *w, whose previously observed value was "value". |
56 | // SpinLockDelay() may do nothing, may yield the CPU, may sleep a clock tick, |
57 | // or may wait for a call to SpinLockWake(w). |
58 | void SpinLockDelay(std::atomic<uint32_t> *w, uint32_t value, int loop, |
59 | base_internal::SchedulingMode scheduling_mode); |
60 | |
61 | // Helper used by AbslInternalSpinLockDelay. |
62 | // Returns a suggested delay in nanoseconds for iteration number "loop". |
63 | int SpinLockSuggestedDelayNS(int loop); |
64 | |
65 | } // namespace base_internal |
66 | ABSL_NAMESPACE_END |
67 | } // namespace absl |
68 | |
69 | // In some build configurations we pass --detect-odr-violations to the |
70 | // gold linker. This causes it to flag weak symbol overrides as ODR |
71 | // violations. Because ODR only applies to C++ and not C, |
72 | // --detect-odr-violations ignores symbols not mangled with C++ names. |
73 | // By changing our extension points to be extern "C", we dodge this |
74 | // check. |
75 | extern "C" { |
76 | void ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockWake)(std::atomic<uint32_t> *w, |
77 | bool all); |
78 | void ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockDelay)( |
79 | std::atomic<uint32_t> *w, uint32_t value, int loop, |
80 | absl::base_internal::SchedulingMode scheduling_mode); |
81 | } |
82 | |
83 | inline void absl::base_internal::SpinLockWake(std::atomic<uint32_t> *w, |
84 | bool all) { |
85 | ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockWake)(w, all); |
86 | } |
87 | |
88 | inline void absl::base_internal::SpinLockDelay( |
89 | std::atomic<uint32_t> *w, uint32_t value, int loop, |
90 | absl::base_internal::SchedulingMode scheduling_mode) { |
91 | ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockDelay) |
92 | (w, value, loop, scheduling_mode); |
93 | } |
94 | |
95 | #endif // ABSL_BASE_INTERNAL_SPINLOCK_WAIT_H_ |
96 | |