Joshua Peraza 441789be5b android: Implement Semaphore with a condition variable and mutex
Bionic uses negative values of a semaphore to represent contention.
`sem_timedwait` fails to restore the value to 0 on timeout resulting in
an error (EBUSY) upon calling `sem_destroy`.

Bug: crashpad:30
Change-Id: If1c73a54a879ebd003b0792ebb8f68ceb83ac8bb
Reviewed-on: https://chromium-review.googlesource.com/894106
Reviewed-by: Mark Mentovai <mark@chromium.org>
Commit-Queue: Joshua Peraza <jperaza@chromium.org>
2018-01-30 21:01:48 +00:00

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// Copyright 2014 The Crashpad Authors. All rights reserved.
//
// 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
//
// http://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.
#ifndef CRASHPAD_UTIL_SYNCHRONIZATION_SEMAPHORE_H_
#define CRASHPAD_UTIL_SYNCHRONIZATION_SEMAPHORE_H_
#include <limits>
#include "build/build_config.h"
#if defined(OS_MACOSX)
#include <dispatch/dispatch.h>
#elif defined(OS_WIN)
#include <windows.h>
#elif defined(OS_ANDROID)
#include <condition_variable>
#include <mutex>
#else
#include <semaphore.h>
#endif
namespace crashpad {
//! \brief An anonymous in-process counting sempahore.
class Semaphore {
public:
//! \brief A TimedWait() argument that causes an indefinite wait.
static constexpr double kIndefiniteWait =
std::numeric_limits<double>::infinity();
//! \brief Initializes the semaphore.
//!
//! \param[in] value The initial value of the semaphore.
//!
//! If the semaphore cannot be created, execution is terminated.
explicit Semaphore(int value);
~Semaphore();
//! \brief Performs the wait (or “procure”) operation on the semaphore.
//!
//! Atomically decrements the value of the semaphore by 1. If the new value is
//! negative, this function blocks and will not return until the semaphores
//! value is incremented to 0 by Signal().
//!
//! \sa TimedWait()
void Wait();
//! \brief Performs a timed wait (or “procure”) operation on the semaphore.
//!
//! \param[in] seconds The maximum number of seconds to wait for the operation
//! to complete. If \a seconds is #kIndefiniteWait, this method behaves as
//! Wait(), and will not time out.
//!
//! \return `false` if the wait timed out, `true` otherwise.
//!
//! This method is simlar to Wait(), except that the amount of time that it
//! blocks is limited.
bool TimedWait(double seconds);
//! \brief Performs the signal (or “post”) operation on the semaphore.
//!
//! Atomically increments the value of the semaphore by 1. If the new value is
//! 0, a caller blocked in Wait() will be awakened.
void Signal();
private:
#if defined(OS_MACOSX)
dispatch_semaphore_t semaphore_;
#elif defined(OS_WIN)
HANDLE semaphore_;
#elif defined(OS_ANDROID)
std::condition_variable cv_;
std::mutex mutex_;
int value_;
#else
sem_t semaphore_;
#endif
};
} // namespace crashpad
#endif // CRASHPAD_UTIL_SYNCHRONIZATION_SEMAPHORE_H_