80 lines
2.8 KiB
C
80 lines
2.8 KiB
C
![]() |
// 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 {
|
||
|
ABSL_NAMESPACE_BEGIN
|
||
|
|
||
|
// 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_ ABSL_GUARDED_BY(lock_);
|
||
|
int num_to_exit_ ABSL_GUARDED_BY(lock_);
|
||
|
};
|
||
|
|
||
|
ABSL_NAMESPACE_END
|
||
|
} // namespace absl
|
||
|
#endif // ABSL_SYNCHRONIZATION_BARRIER_H_
|