Abseil Common Libraries (C++) (grcp 依赖)
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77 lines
2.7 KiB
77 lines
2.7 KiB
// Copyright 2017 The Abseil Authors. |
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// |
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// Licensed under the Apache License, Version 2.0 (the "License"); |
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// you may not use this file except in compliance with the License. |
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// You may obtain a copy of the License at |
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// |
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// http://www.apache.org/licenses/LICENSE-2.0 |
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// |
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// Unless required by applicable law or agreed to in writing, software |
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// distributed under the License is distributed on an "AS IS" BASIS, |
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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// See the License for the specific language governing permissions and |
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// limitations under the License. |
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// |
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// ----------------------------------------------------------------------------- |
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// barrier.h |
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// ----------------------------------------------------------------------------- |
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#ifndef ABSL_SYNCHRONIZATION_BARRIER_H_ |
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#define ABSL_SYNCHRONIZATION_BARRIER_H_ |
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#include "absl/base/thread_annotations.h" |
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#include "absl/synchronization/mutex.h" |
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namespace absl { |
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// Barrier |
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// |
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// This class creates a barrier which blocks threads until a prespecified |
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// threshold of threads (`num_threads`) utilizes the barrier. A thread utilizes |
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// the `Barrier` by calling `Block()` on the barrier, which will block that |
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// thread; no call to `Block()` will return until `num_threads` threads have |
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// called it. |
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// |
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// Exactly one call to `Block()` will return `true`, which is then responsible |
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// for destroying the barrier; because stack allocation will cause the barrier |
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// to be deleted when it is out of scope, barriers should not be stack |
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// allocated. |
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// |
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// Example: |
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// |
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// // Main thread creates a `Barrier`: |
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// barrier = new Barrier(num_threads); |
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// |
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// // Each participating thread could then call: |
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// if (barrier->Block()) delete barrier; // Exactly one call to `Block()` |
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// // returns `true`; that call |
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// // deletes the barrier. |
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class Barrier { |
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public: |
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// `num_threads` is the number of threads that will participate in the barrier |
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explicit Barrier(int num_threads) |
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: num_to_block_(num_threads), num_to_exit_(num_threads) {} |
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Barrier(const Barrier&) = delete; |
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Barrier& operator=(const Barrier&) = delete; |
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// Barrier::Block() |
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// |
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// Blocks the current thread, and returns only when the `num_threads` |
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// threshold of threads utilizing this barrier has been reached. `Block()` |
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// returns `true` for precisely one caller, which may then destroy the |
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// barrier. |
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// |
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// Memory ordering: For any threads X and Y, any action taken by X |
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// before X calls `Block()` will be visible to Y after Y returns from |
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// `Block()`. |
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bool Block(); |
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private: |
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Mutex lock_; |
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int num_to_block_ GUARDED_BY(lock_); |
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int num_to_exit_ GUARDED_BY(lock_); |
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}; |
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} // namespace absl |
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#endif // ABSL_SYNCHRONIZATION_BARRIER_H_
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