libdatachannel/include/rtc/utils.hpp

/**
 * Copyright (c) 2019-2021 Paul-Louis Ageneau
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#ifndef RTC_UTILS_H
#define RTC_UTILS_H

#include <functional>
#include <memory>
#include <mutex>

namespace rtc {

// overloaded helper
template <class... Ts> struct overloaded : Ts... { using Ts::operator()...; };
template <class... Ts> overloaded(Ts...) -> overloaded<Ts...>;

// weak_ptr bind helper
template <typename F, typename T, typename... Args> auto weak_bind(F &&f, T *t, Args &&..._args) {
	return [bound = std::bind(f, t, _args...), weak_this = t->weak_from_this()](auto &&...args) {
		using result_type = typename decltype(bound)::result_type;
		if (auto shared_this = weak_this.lock())
			return bound(args...);
		else
			return static_cast<result_type>(false);
	};
}

// scope_guard helper
class scope_guard {
public:
	scope_guard(std::function<void()> func) : function(std::move(func)) {}
	scope_guard(scope_guard &&other) = delete;
	scope_guard(const scope_guard &) = delete;
	void operator=(const scope_guard &) = delete;

	~scope_guard() {
		if (function)
			function();
	}

private:
	std::function<void()> function;
};

// callback with built-in synchronization
template <typename... Args> class synchronized_callback {
public:
	synchronized_callback() = default;
	synchronized_callback(synchronized_callback &&cb) { *this = std::move(cb); }
	synchronized_callback(const synchronized_callback &cb) { *this = cb; }
	synchronized_callback(std::function<void(Args...)> func) { *this = std::move(func); }
	~synchronized_callback() { *this = nullptr; }

	synchronized_callback &operator=(synchronized_callback &&cb) {
		std::scoped_lock lock(mutex, cb.mutex);
		callback = std::move(cb.callback);
		cb.callback = nullptr;
		return *this;
	}

	synchronized_callback &operator=(const synchronized_callback &cb) {
		std::scoped_lock lock(mutex, cb.mutex);
		callback = cb.callback;
		return *this;
	}

	synchronized_callback &operator=(std::function<void(Args...)> func) {
		std::lock_guard lock(mutex);
		callback = std::move(func);
		return *this;
	}

	void operator()(Args... args) const {
		std::lock_guard lock(mutex);
		if (callback)
			callback(std::move(args)...);
	}

	operator bool() const {
		std::lock_guard lock(mutex);
		return callback ? true : false;
	}

	std::function<void(Args...)> wrap() const {
		return [this](Args... args) { (*this)(std::move(args)...); };
	}

private:
	std::function<void(Args...)> callback;
	mutable std::recursive_mutex mutex;
};

// pimpl base class
template <typename T> using impl_ptr = std::shared_ptr<T>;
template <typename T> class CheshireCat {
public:
	CheshireCat(impl_ptr<T> impl) : mImpl(std::move(impl)) {}
	template <typename... Args>
	CheshireCat(Args... args) : mImpl(std::make_shared<T>(std::move(args)...)) {}

	virtual ~CheshireCat() = default;

protected:
	impl_ptr<T> impl() { return mImpl; }
	impl_ptr<const T> impl() const { return mImpl; }

private:
	impl_ptr<T> mImpl;
};

} // namespace rtc

#endif