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Telegram/lib_base/base/binary_guard.h

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+// This file is part of Desktop App Toolkit,
+// a set of libraries for developing nice desktop applications.
+//
+// For license and copyright information please follow this link:
+// https://github.com/desktop-app/legal/blob/master/LEGAL
+//
+#pragma once
+
+#include "base/algorithm.h"
+
+#include <atomic>
+
+namespace base {
+
+class binary_guard {
+public:
+	binary_guard() = default;
+	binary_guard(binary_guard &&other);
+	binary_guard &operator=(binary_guard &&other);
+	~binary_guard();
+
+	binary_guard &operator=(std::nullptr_t);
+
+	bool alive() const;
+	binary_guard make_guard();
+
+	explicit operator bool() const;
+
+private:
+	void destroy();
+
+	std::atomic<bool> *_bothAlive = nullptr;
+
+};
+
+inline binary_guard::binary_guard(binary_guard &&other)
+: _bothAlive(base::take(other._bothAlive)) {
+}
+
+inline binary_guard &binary_guard::operator=(binary_guard &&other) {
+	if (this != &other) {
+		destroy();
+		_bothAlive = base::take(other._bothAlive);
+	}
+	return *this;
+}
+
+inline binary_guard::~binary_guard() {
+	destroy();
+}
+
+inline binary_guard &binary_guard::operator=(std::nullptr_t) {
+	destroy();
+	return *this;
+}
+
+inline binary_guard::operator bool() const {
+	return alive();
+}
+
+inline bool binary_guard::alive() const {
+	return _bothAlive && _bothAlive->load();
+}
+
+inline void binary_guard::destroy() {
+	if (const auto both = base::take(_bothAlive)) {
+		auto old = true;
+		if (!both->compare_exchange_strong(old, false)) {
+			delete both;
+		}
+	}
+}
+
+inline binary_guard binary_guard::make_guard() {
+	destroy();
+
+	auto result = binary_guard();
+	_bothAlive = result._bothAlive = new std::atomic<bool>(true);
+	return result;
+}
+
+} // namespace base
+
+namespace crl {
+
+template <typename T, typename Enable>
+struct guard_traits;
+
+template <>
+struct guard_traits<base::binary_guard, void> {
+	static base::binary_guard create(base::binary_guard value) {
+		return value;
+	}
+	static bool check(const base::binary_guard &guard) {
+		return guard.alive();
+	}
+
+};
+
+} // namespace crl