// SPDX-License-Identifier: BSD-2-Clause
// author: Max Kellermann <max.kellermann@gmail.com>

#ifndef THREAD_ID_HXX
#define THREAD_ID_HXX

#ifdef _WIN32
#include <processthreadsapi.h>
#else
#include <pthread.h>
#endif

/**
 * A low-level identification for a thread.  Designed to work with
 * existing threads, such as the main thread.  Mostly useful for
 * debugging code.
 */
class ThreadId {
#ifdef _WIN32
	DWORD id;
#else
	pthread_t id;
#endif

public:
	/**
	 * No initialisation.
	 */
	ThreadId() noexcept = default;

#ifdef _WIN32
	constexpr ThreadId(DWORD _id) noexcept:id(_id) {}
#else
	constexpr ThreadId(pthread_t _id) noexcept:id(_id) {}
#endif

	static constexpr ThreadId Null() noexcept {
#ifdef _WIN32
		return 0;
#else
		return pthread_t();
#endif
	}

	[[gnu::pure]]
	bool IsNull() const noexcept {
		return *this == Null();
	}

	/**
	 * Return the current thread's id .
	 */
	[[gnu::pure]]
	static const ThreadId GetCurrent() noexcept {
#ifdef _WIN32
		return ::GetCurrentThreadId();
#else
		return pthread_self();
#endif
	}

	[[gnu::pure]]
	bool operator==(const ThreadId &other) const noexcept {
		/* note: not using pthread_equal() because that
		   function "is undefined if either thread ID is not
		   valid so we can't safely use it on
		   default-constructed values" (comment from
		   libstdc++) - and if both libstdc++ and libc++ get
		   away with this, we can do it as well */
		return id == other.id;
	}

	/**
	 * Check if this thread is the current thread.
	 */
	bool IsInside() const noexcept {
		return *this == GetCurrent();
	}
};

#endif