spinlock_wait.h
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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 
25 
26 namespace absl {
27 namespace base_internal {
28 
29 // SpinLockWait() waits until it can perform one of several transitions from
30 // "from" to "to". It returns when it performs a transition where done==true.
32  uint32_t from;
33  uint32_t to;
34  bool done;
35 };
36 
37 // Wait until *w can transition from trans[i].from to trans[i].to for some i
38 // satisfying 0<=i<n && trans[i].done, atomically make the transition,
39 // then return the old value of *w. Make any other atomic transitions
40 // where !trans[i].done, but continue waiting.
41 uint32_t SpinLockWait(std::atomic<uint32_t> *w, int n,
42  const SpinLockWaitTransition trans[],
43  SchedulingMode scheduling_mode);
44 
45 // If possible, wake some thread that has called SpinLockDelay(w, ...). If
46 // "all" is true, wake all such threads. This call is a hint, and on some
47 // systems it may be a no-op; threads calling SpinLockDelay() will always wake
48 // eventually even if SpinLockWake() is never called.
49 void SpinLockWake(std::atomic<uint32_t> *w, bool all);
50 
51 // Wait for an appropriate spin delay on iteration "loop" of a
52 // spin loop on location *w, whose previously observed value was "value".
53 // SpinLockDelay() may do nothing, may yield the CPU, may sleep a clock tick,
54 // or may wait for a delay that can be truncated by a call to SpinLockWake(w).
55 // In all cases, it must return in bounded time even if SpinLockWake() is not
56 // called.
57 void SpinLockDelay(std::atomic<uint32_t> *w, uint32_t value, int loop,
58  base_internal::SchedulingMode scheduling_mode);
59 
60 // Helper used by AbslInternalSpinLockDelay.
61 // Returns a suggested delay in nanoseconds for iteration number "loop".
62 int SpinLockSuggestedDelayNS(int loop);
63 
64 } // namespace base_internal
65 } // namespace absl
66 
67 // In some build configurations we pass --detect-odr-violations to the
68 // gold linker. This causes it to flag weak symbol overrides as ODR
69 // violations. Because ODR only applies to C++ and not C,
70 // --detect-odr-violations ignores symbols not mangled with C++ names.
71 // By changing our extension points to be extern "C", we dodge this
72 // check.
73 extern "C" {
74 void AbslInternalSpinLockWake(std::atomic<uint32_t> *w, bool all);
76  std::atomic<uint32_t> *w, uint32_t value, int loop,
77  absl::base_internal::SchedulingMode scheduling_mode);
78 }
79 
80 inline void absl::base_internal::SpinLockWake(std::atomic<uint32_t> *w,
81  bool all) {
83 }
84 
86  std::atomic<uint32_t> *w, uint32_t value, int loop,
87  absl::base_internal::SchedulingMode scheduling_mode) {
88  AbslInternalSpinLockDelay(w, value, loop, scheduling_mode);
89 }
90 
91 #endif // ABSL_BASE_INTERNAL_SPINLOCK_WAIT_H_
void AbslInternalSpinLockDelay(std::atomic< uint32_t > *w, uint32_t value, int loop, absl::base_internal::SchedulingMode scheduling_mode)
void SpinLockDelay(std::atomic< uint32_t > *w, uint32_t value, int loop, base_internal::SchedulingMode scheduling_mode)
Definition: spinlock_wait.h:85
void AbslInternalSpinLockWake(std::atomic< uint32_t > *w, bool all)
uint32_t SpinLockWait(std::atomic< uint32_t > *w, int n, const SpinLockWaitTransition trans[], base_internal::SchedulingMode scheduling_mode)
Definition: algorithm.h:29
void SpinLockWake(std::atomic< uint32_t > *w, bool all)
Definition: spinlock_wait.h:80
size_t value
int SpinLockSuggestedDelayNS(int loop)


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autogenerated on Wed Jun 19 2019 19:19:58