rpcs3/Utilities/SharedMutex.h

#pragma once

#include <shared_mutex>

// An attempt to create lock-free (in optimistic case) implementation similar to std::shared_mutex;
// MSVC implementation of std::shared_timed_mutex is not lock-free and thus may be slow, and std::shared_mutex is not available.
class shared_mutex_t
{
	struct ownership_info_t
	{
		u32 readers : 31;
		u32 writers : 1;
		u16 waiting_readers;
		u16 waiting_writers;
	};

	atomic_t<ownership_info_t> m_info{};

	std::mutex m_mutex;
	
	std::condition_variable m_rcv;
	std::condition_variable m_wcv;
	std::condition_variable m_wrcv;
	std::condition_variable m_wwcv;

public:
	shared_mutex_t() = default;

	// Lock in shared mode
	void lock_shared();

	// Try to lock in shared mode
	bool try_lock_shared();

	// Unlock in shared mode
	void unlock_shared();

	// Lock exclusively
	void lock();

	// Try to lock exclusively
	bool try_lock();

	// Unlock exclusively
	void unlock();
};