Abseil Common Libraries (C++) (grcp 依赖)
https://abseil.io/
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
77 lines
2.8 KiB
77 lines
2.8 KiB
// Copyright 2017 The Abseil Authors. |
|
// |
|
// Licensed under the Apache License, Version 2.0 (the "License"); |
|
// you may not use this file except in compliance with the License. |
|
// You may obtain a copy of the License at |
|
// |
|
// https://www.apache.org/licenses/LICENSE-2.0 |
|
// |
|
// Unless required by applicable law or agreed to in writing, software |
|
// distributed under the License is distributed on an "AS IS" BASIS, |
|
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
|
// See the License for the specific language governing permissions and |
|
// limitations under the License. |
|
// |
|
// ----------------------------------------------------------------------------- |
|
// barrier.h |
|
// ----------------------------------------------------------------------------- |
|
|
|
#ifndef ABSL_SYNCHRONIZATION_BARRIER_H_ |
|
#define ABSL_SYNCHRONIZATION_BARRIER_H_ |
|
|
|
#include "absl/base/thread_annotations.h" |
|
#include "absl/synchronization/mutex.h" |
|
|
|
namespace absl { |
|
|
|
// Barrier |
|
// |
|
// This class creates a barrier which blocks threads until a prespecified |
|
// threshold of threads (`num_threads`) utilizes the barrier. A thread utilizes |
|
// the `Barrier` by calling `Block()` on the barrier, which will block that |
|
// thread; no call to `Block()` will return until `num_threads` threads have |
|
// called it. |
|
// |
|
// Exactly one call to `Block()` will return `true`, which is then responsible |
|
// for destroying the barrier; because stack allocation will cause the barrier |
|
// to be deleted when it is out of scope, barriers should not be stack |
|
// allocated. |
|
// |
|
// Example: |
|
// |
|
// // Main thread creates a `Barrier`: |
|
// barrier = new Barrier(num_threads); |
|
// |
|
// // Each participating thread could then call: |
|
// if (barrier->Block()) delete barrier; // Exactly one call to `Block()` |
|
// // returns `true`; that call |
|
// // deletes the barrier. |
|
class Barrier { |
|
public: |
|
// `num_threads` is the number of threads that will participate in the barrier |
|
explicit Barrier(int num_threads) |
|
: num_to_block_(num_threads), num_to_exit_(num_threads) {} |
|
|
|
Barrier(const Barrier&) = delete; |
|
Barrier& operator=(const Barrier&) = delete; |
|
|
|
// Barrier::Block() |
|
// |
|
// Blocks the current thread, and returns only when the `num_threads` |
|
// threshold of threads utilizing this barrier has been reached. `Block()` |
|
// returns `true` for precisely one caller, which may then destroy the |
|
// barrier. |
|
// |
|
// Memory ordering: For any threads X and Y, any action taken by X |
|
// before X calls `Block()` will be visible to Y after Y returns from |
|
// `Block()`. |
|
bool Block(); |
|
|
|
private: |
|
Mutex lock_; |
|
int num_to_block_ GUARDED_BY(lock_); |
|
int num_to_exit_ GUARDED_BY(lock_); |
|
}; |
|
|
|
} // namespace absl |
|
#endif // ABSL_SYNCHRONIZATION_BARRIER_H_
|
|
|