godot/core/os/semaphore.h

/*************************************************************************/
/*  semaphore.h                                                          */
/*************************************************************************/
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/*                           GODOT ENGINE                                */
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/* Copyright (c) 2007-2020 Juan Linietsky, Ariel Manzur.                 */
/* Copyright (c) 2014-2020 Godot Engine contributors (cf. AUTHORS.md).   */
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#ifndef SEMAPHORE_H
#define SEMAPHORE_H

#include "core/error_list.h"
#include "core/typedefs.h"

#if !defined(NO_THREADS)

#include <condition_variable>
#include <mutex>

class Semaphore {
private:
	mutable std::mutex mutex_;
	mutable std::condition_variable condition_;
	mutable unsigned long count_ = 0; // Initialized as locked.

public:
	_ALWAYS_INLINE_ void post() const {
		std::lock_guard<decltype(mutex_)> lock(mutex_);
		++count_;
		condition_.notify_one();
	}

	_ALWAYS_INLINE_ void wait() const {
		std::unique_lock<decltype(mutex_)> lock(mutex_);
		while (!count_) // Handle spurious wake-ups.
			condition_.wait(lock);
		--count_;
	}

	_ALWAYS_INLINE_ bool try_wait() const {
		std::lock_guard<decltype(mutex_)> lock(mutex_);
		if (count_) {
			--count_;
			return true;
		}
		return false;
	}
};

#else

class Semaphore {
public:
	_ALWAYS_INLINE_ void post() const {}
	_ALWAYS_INLINE_ void wait() const {}
	_ALWAYS_INLINE_ bool try_wait() const { return true; }
};

#endif

#endif // SEMAPHORE_H