semaphore.h

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/*
 * Copyright (c) 2020 Roc Streaming authors
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */
 
//! @file roc_core/target_posix_ext/roc_core/semaphore.h
//! @brief Semaphore.
 
#ifndef ROC_CORE_SEMAPHORE_H_
#define ROC_CORE_SEMAPHORE_H_
 
#include <semaphore.h>
 
#include "roc_core/atomic.h"
#include "roc_core/attributes.h"
#include "roc_core/noncopyable.h"
#include "roc_core/time.h"
 
namespace roc {
namespace core {
 
//! Semaphore.
class Semaphore : public NonCopyable<> {
public:
    //! Initialize semaphore with given counter.
    explicit Semaphore(unsigned counter = 0);
 
    ~Semaphore();
 
    //! Wait until the counter becomes non-zero, decrement it, and return true.
    //! If deadline expires before the counter becomes non-zero, returns false.
    //! Deadline should be in the same time domain as core::timestamp().
    ROC_ATTR_NODISCARD bool timed_wait(nanoseconds_t deadline);
 
    //! Wait until the counter becomes non-zero, decrement it, and return.
    void wait();
 
    //! Increment counter and wake up blocked waits.
    //! This method is lock-free at least on recent glibc and musl versions
    //! (which implement POSIX semaphores using a futex and an atomic).
    void post();
 
private:
    sem_t sem_;
    Atomic<int> guard_;
};
 
} // namespace core
} // namespace roc
 
#endif // ROC_CORE_SEMAPHORE_H_