barrier.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 // -----------------------------------------------------------------------------
16 // barrier.h
17 // -----------------------------------------------------------------------------
18 
19 #ifndef ABSL_SYNCHRONIZATION_BARRIER_H_
20 #define ABSL_SYNCHRONIZATION_BARRIER_H_
21 
24 
25 namespace absl {
26 
27 // Barrier
28 //
29 // This class creates a barrier which blocks threads until a prespecified
30 // threshold of threads (`num_threads`) utilizes the barrier. A thread utilizes
31 // the `Barrier` by calling `Block()` on the barrier, which will block that
32 // thread; no call to `Block()` will return until `num_threads` threads have
33 // called it.
34 //
35 // Exactly one call to `Block()` will return `true`, which is then responsible
36 // for destroying the barrier; because stack allocation will cause the barrier
37 // to be deleted when it is out of scope, barriers should not be stack
38 // allocated.
39 //
40 // Example:
41 //
42 // // Main thread creates a `Barrier`:
43 // barrier = new Barrier(num_threads);
44 //
45 // // Each participating thread could then call:
46 // if (barrier->Block()) delete barrier; // Exactly one call to `Block()`
47 // // returns `true`; that call
48 // // deletes the barrier.
49 class Barrier {
50  public:
51  // `num_threads` is the number of threads that will participate in the barrier
52  explicit Barrier(int num_threads)
53  : num_to_block_(num_threads), num_to_exit_(num_threads) {}
54 
55  Barrier(const Barrier&) = delete;
56  Barrier& operator=(const Barrier&) = delete;
57 
58  // Barrier::Block()
59  //
60  // Blocks the current thread, and returns only when the `num_threads`
61  // threshold of threads utilizing this barrier has been reached. `Block()`
62  // returns `true` for precisely one caller, which may then destroy the
63  // barrier.
64  //
65  // Memory ordering: For any threads X and Y, any action taken by X
66  // before X calls `Block()` will be visible to Y after Y returns from
67  // `Block()`.
68  bool Block();
69 
70  private:
72  int num_to_block_ GUARDED_BY(lock_);
73  int num_to_exit_ GUARDED_BY(lock_);
74 };
75 
76 } // namespace absl
77 #endif // ABSL_SYNCHRONIZATION_BARRIER_H_
Barrier(int num_threads)
Definition: barrier.h:52
Definition: algorithm.h:29
bool Block()
Definition: barrier.cc:27
Mutex lock_
Definition: barrier.h:71
Barrier & operator=(const Barrier &)=delete
int num_to_block_ GUARDED_BY(lock_)


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autogenerated on Mon Feb 28 2022 21:31:17