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Telegram/lib_base/base/file_lock_win.cpp

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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
+//
+#include "base/file_lock.h"
+
+#include "base/platform/win/base_file_utilities_win.h"
+
+#include <QtCore/QDir>
+
+#include <windows.h>
+#include <io.h>
+#include <fileapi.h>
+
+namespace base {
+
+class FileLock::Lock {
+public:
+	static int Acquire(const QFile &file);
+
+	explicit Lock(int descriptor);
+	~Lock();
+
+private:
+	static constexpr auto offsetLow = DWORD(kLockOffset);
+	static constexpr auto offsetHigh = DWORD(0);
+	static constexpr auto limitLow = DWORD(kLockLimit);
+	static constexpr auto limitHigh = DWORD(0);
+
+	int _descriptor = 0;
+
+};
+
+int FileLock::Lock::Acquire(const QFile &file) {
+	const auto descriptor = file.handle();
+	if (!descriptor || !file.isOpen()) {
+		return false;
+	}
+	const auto handle = HANDLE(_get_osfhandle(descriptor));
+	if (!handle) {
+		return false;
+	}
+	return LockFile(handle, offsetLow, offsetHigh, limitLow, limitHigh)
+		? descriptor
+		: 0;
+}
+
+FileLock::Lock::Lock(int descriptor) : _descriptor(descriptor) {
+}
+
+FileLock::Lock::~Lock() {
+	if (const auto handle = HANDLE(_get_osfhandle(_descriptor))) {
+		UnlockFile(handle, offsetLow, offsetHigh, limitLow, limitHigh);
+	}
+}
+
+FileLock::FileLock() = default;
+
+bool FileLock::lock(QFile &file, QIODevice::OpenMode mode) {
+	Expects(_lock == nullptr || file.isOpen());
+
+	unlock();
+	file.close();
+	do {
+		if (!file.open(mode)) {
+			return false;
+		} else if (const auto descriptor = Lock::Acquire(file)) {
+			_lock = std::make_unique<Lock>(descriptor);
+			return true;
+		}
+		file.close();
+	} while (Platform::CloseProcesses(file.fileName()));
+
+	return false;
+}
+
+bool FileLock::locked() const {
+	return (_lock != nullptr);
+}
+
+void FileLock::unlock() {
+	_lock = nullptr;
+}
+
+FileLock::~FileLock() = default;
+
+} // namespace base