thread.h

/**************************************************************************/
/*  thread.h                                                              */
/**************************************************************************/
/*                         This file is part of:                          */
/*                             GODOT ENGINE                               */
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/* Copyright (c) 2014-present Godot Engine contributors (see AUTHORS.md). */
/* Copyright (c) 2007-2014 Juan Linietsky, Ariel Manzur.                  */
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#pragma once

#include "platform_config.h"

// Define PLATFORM_THREAD_OVERRIDE in your platform's `platform_config.h`
// to use a custom Thread implementation defined in `platform/[your_platform]/platform_thread.h`.
// Overriding the Thread implementation is required in some proprietary platforms.

#ifdef PLATFORM_THREAD_OVERRIDE

#include "platform_thread.h"

#else

#include "core/typedefs.h"

#ifdef THREADS_ENABLED

#include "core/templates/safe_refcount.h"

#include <new> // IWYU pragma: keep // For hardware interference size.

#ifdef MINGW_ENABLED
#define MINGW_STDTHREAD_REDUNDANCY_WARNING
#include "thirdparty/mingw-std-threads/mingw.thread.h"
#define THREADING_NAMESPACE mingw_stdthread
#else
#include <thread>
#define THREADING_NAMESPACE std
#endif

class String;

class Thread {
public:
	typedef void (*Callback)(void *p_userdata);

	typedef uint64_t ID;

	enum : ID {
		UNASSIGNED_ID = 0,
		MAIN_ID = 1
	};

	enum Priority {
		PRIORITY_LOW,
		PRIORITY_NORMAL,
		PRIORITY_HIGH
	};

	struct Settings {
		Priority priority;
		Settings() { priority = PRIORITY_NORMAL; }
	};

	struct PlatformFunctions {
		Error (*set_name)(const String &) = nullptr;
		void (*set_priority)(Thread::Priority) = nullptr;
		void (*init)() = nullptr;
		void (*wrapper)(Thread::Callback, void *) = nullptr;
		void (*term)() = nullptr;
	};

#if defined(__cpp_lib_hardware_interference_size) && !defined(ANDROID_ENABLED) // This would be OK with NDK >= 26.
	GODOT_GCC_WARNING_PUSH_AND_IGNORE("-Winterference-size")
	static constexpr size_t CACHE_LINE_BYTES = std::hardware_destructive_interference_size;
	GODOT_GCC_WARNING_POP
#else
	// At a negligible memory cost, we use a conservatively high value.
	static constexpr size_t CACHE_LINE_BYTES = 128;
#endif

private:
	friend class Main;

	static PlatformFunctions platform_functions;

	ID id = UNASSIGNED_ID;

	static SafeNumeric<uint64_t> id_counter;
	static thread_local ID caller_id;
	THREADING_NAMESPACE::thread thread;

	static void callback(ID p_caller_id, const Settings &p_settings, Thread::Callback p_callback, void *p_userdata);

	static void make_main_thread() { caller_id = MAIN_ID; }
	static void release_main_thread() { caller_id = id_counter.increment(); }

public:
	static void _set_platform_functions(const PlatformFunctions &p_functions);

	_FORCE_INLINE_ static void yield() { std::this_thread::yield(); }

	_FORCE_INLINE_ ID get_id() const { return id; }
	// get the ID of the caller thread
	_FORCE_INLINE_ static ID get_caller_id() {
		return caller_id;
	}
	// get the ID of the main thread
	_FORCE_INLINE_ static ID get_main_id() { return MAIN_ID; }

	_FORCE_INLINE_ static bool is_main_thread() { return caller_id == MAIN_ID; } // Gain a tiny bit of perf here because there is no need to validate caller_id here, because only main thread will be set as 1.

	static Error set_name(const String &p_name);

	ID start(Thread::Callback p_callback, void *p_user, const Settings &p_settings = Settings());
	bool is_started() const;
	///< waits until thread is finished, and deallocates it.
	void wait_to_finish();

	Thread();
	~Thread();
};

#else // No threads.

class String;

class Thread {
public:
	typedef void (*Callback)(void *p_userdata);

	typedef uint64_t ID;

	static constexpr size_t CACHE_LINE_BYTES = sizeof(void *);

	enum : ID {
		UNASSIGNED_ID = 0,
		MAIN_ID = 1
	};

	enum Priority {
		PRIORITY_LOW,
		PRIORITY_NORMAL,
		PRIORITY_HIGH
	};

	struct Settings {
		Priority priority;
		Settings() { priority = PRIORITY_NORMAL; }
	};

	struct PlatformFunctions {
		Error (*set_name)(const String &) = nullptr;
		void (*set_priority)(Thread::Priority) = nullptr;
		void (*init)() = nullptr;
		void (*wrapper)(Thread::Callback, void *) = nullptr;
		void (*term)() = nullptr;
	};

private:
	friend class Main;

	static PlatformFunctions platform_functions;

	static void make_main_thread() {}
	static void release_main_thread() {}

public:
	static void _set_platform_functions(const PlatformFunctions &p_functions);

	_FORCE_INLINE_ ID get_id() const { return 0; }
	_FORCE_INLINE_ static ID get_caller_id() { return MAIN_ID; }
	_FORCE_INLINE_ static ID get_main_id() { return MAIN_ID; }

	_FORCE_INLINE_ static bool is_main_thread() { return true; }

	static Error set_name(const String &p_name) { return ERR_UNAVAILABLE; }

	void start(Thread::Callback p_callback, void *p_user, const Settings &p_settings = Settings()) {}
	bool is_started() const { return false; }
	void wait_to_finish() {}
};

#endif // THREADS_ENABLED

#endif // PLATFORM_THREAD_OVERRIDE