Abseil Common Libraries (C++) (grcp 依赖) https://abseil.io/
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7 years ago
// 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
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//
// 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 {
Export of internal Abseil changes -- c99f979ad34f155fbeeea69b88bdc7458d89a21c by Derek Mauro <dmauro@google.com>: Remove a floating point division by zero test. This isn't testing behavior related to the library, and MSVC warns about it in opt mode. PiperOrigin-RevId: 285220804 -- 68b015491f0dbf1ab547994673281abd1f34cd4b by Gennadiy Rozental <rogeeff@google.com>: This CL introduces following changes to the class FlagImpl: * We eliminate the CommandLineFlagLocks struct. Instead callback guard and callback function are combined into a single CallbackData struct, while primary data lock is stored separately. * CallbackData member of class FlagImpl is initially set to be nullptr and is only allocated and initialized when a flag's callback is being set. For most flags we do not pay for the extra space and extra absl::Mutex now. * Primary data guard is stored in data_guard_ data member. This is a properly aligned character buffer of necessary size. During initialization of the flag we construct absl::Mutex in this space using placement new call. * We now avoid extra value copy after successful attempt to parse value out of string. Instead we swap flag's current value with tentative value we just produced. PiperOrigin-RevId: 285132636 -- ed45d118fb818969eb13094cf7827c885dfc562c by Tom Manshreck <shreck@google.com>: Change null-term* (and nul-term*) to NUL-term* in comments PiperOrigin-RevId: 285036610 -- 729619017944db895ce8d6d29c1995aa2e5628a5 by Derek Mauro <dmauro@google.com>: Use the Posix implementation of thread identity on MinGW. Some versions of MinGW suffer from thread_local bugs. PiperOrigin-RevId: 285022920 -- 39a25493503c76885bc3254c28f66a251c5b5bb0 by Greg Falcon <gfalcon@google.com>: Implementation detail change. Add further ABSL_NAMESPACE_BEGIN and _END annotation macros to files in Abseil. PiperOrigin-RevId: 285012012 GitOrigin-RevId: c99f979ad34f155fbeeea69b88bdc7458d89a21c Change-Id: I4c85d3704e45d11a9ac50d562f39640a6adbedc1
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ABSL_NAMESPACE_BEGIN
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// 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_);
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};
Export of internal Abseil changes -- c99f979ad34f155fbeeea69b88bdc7458d89a21c by Derek Mauro <dmauro@google.com>: Remove a floating point division by zero test. This isn't testing behavior related to the library, and MSVC warns about it in opt mode. PiperOrigin-RevId: 285220804 -- 68b015491f0dbf1ab547994673281abd1f34cd4b by Gennadiy Rozental <rogeeff@google.com>: This CL introduces following changes to the class FlagImpl: * We eliminate the CommandLineFlagLocks struct. Instead callback guard and callback function are combined into a single CallbackData struct, while primary data lock is stored separately. * CallbackData member of class FlagImpl is initially set to be nullptr and is only allocated and initialized when a flag's callback is being set. For most flags we do not pay for the extra space and extra absl::Mutex now. * Primary data guard is stored in data_guard_ data member. This is a properly aligned character buffer of necessary size. During initialization of the flag we construct absl::Mutex in this space using placement new call. * We now avoid extra value copy after successful attempt to parse value out of string. Instead we swap flag's current value with tentative value we just produced. PiperOrigin-RevId: 285132636 -- ed45d118fb818969eb13094cf7827c885dfc562c by Tom Manshreck <shreck@google.com>: Change null-term* (and nul-term*) to NUL-term* in comments PiperOrigin-RevId: 285036610 -- 729619017944db895ce8d6d29c1995aa2e5628a5 by Derek Mauro <dmauro@google.com>: Use the Posix implementation of thread identity on MinGW. Some versions of MinGW suffer from thread_local bugs. PiperOrigin-RevId: 285022920 -- 39a25493503c76885bc3254c28f66a251c5b5bb0 by Greg Falcon <gfalcon@google.com>: Implementation detail change. Add further ABSL_NAMESPACE_BEGIN and _END annotation macros to files in Abseil. PiperOrigin-RevId: 285012012 GitOrigin-RevId: c99f979ad34f155fbeeea69b88bdc7458d89a21c Change-Id: I4c85d3704e45d11a9ac50d562f39640a6adbedc1
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ABSL_NAMESPACE_END
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} // namespace absl
#endif // ABSL_SYNCHRONIZATION_BARRIER_H_