sneedmc/libraries/LocalPeer/src/LockedFile_win.cpp

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#include "LockedFile.h"
#include <qt_windows.h>
#include <QFileInfo>

#define MUTEX_PREFIX "QtLockedFile mutex "
// Maximum number of concurrent read locks. Must not be greater than MAXIMUM_WAIT_OBJECTS
#define MAX_READERS MAXIMUM_WAIT_OBJECTS

Qt::HANDLE LockedFile::getMutexHandle(int idx, bool doCreate)
{
	if (mutexname.isEmpty()) {
		QFileInfo fi(*this);
		mutexname = QString::fromLatin1(MUTEX_PREFIX)
					+ fi.absoluteFilePath().toLower();
	}
	QString mname(mutexname);
	if (idx >= 0)
		mname += QString::number(idx);

	Qt::HANDLE mutex;
	if (doCreate) {
		mutex = CreateMutexW(NULL, FALSE, (LPCWSTR)mname.utf16());
		if (!mutex) {
			qErrnoWarning("QtLockedFile::lock(): CreateMutex failed");
			return 0;
		}
	}
	else {
		OpenMutexW(SYNCHRONIZE | MUTEX_MODIFY_STATE, FALSE, (LPCWSTR)mname.utf16());
		if (!mutex) {
			if (GetLastError() != ERROR_FILE_NOT_FOUND)
				qErrnoWarning("QtLockedFile::lock(): OpenMutex failed");
			return 0;
		}
	}
	return mutex;
}

bool LockedFile::waitMutex(Qt::HANDLE mutex, bool doBlock)
{
	Q_ASSERT(mutex);
	DWORD res = WaitForSingleObject(mutex, doBlock ? INFINITE : 0);
	switch (res) {
	case WAIT_OBJECT_0:
	case WAIT_ABANDONED:
		return true;
		break;
	case WAIT_TIMEOUT:
		break;
	default:
		qErrnoWarning("QtLockedFile::lock(): WaitForSingleObject failed");
	}
	return false;
}



bool LockedFile::lock(LockMode mode, bool block)
{
	if (!isOpen()) {
		qWarning("QtLockedFile::lock(): file is not opened");
		return false;
	}

	if (mode == NoLock)
		return unlock();

	if (mode == m_lock_mode)
		return true;

	if (m_lock_mode != NoLock)
		unlock();

	if (!wmutex && !(wmutex = getMutexHandle(-1, true)))
		return false;

	if (!waitMutex(wmutex, block))
		return false;

	if (mode == ReadLock) {
		int idx = 0;
		for (; idx < MAX_READERS; idx++) {
			rmutex = getMutexHandle(idx, false);
			if (!rmutex || waitMutex(rmutex, false))
				break;
			CloseHandle(rmutex);
		}
		bool ok = true;
		if (idx >= MAX_READERS) {
			qWarning("QtLockedFile::lock(): too many readers");
			rmutex = 0;
			ok = false;
		}
		else if (!rmutex) {
			rmutex = getMutexHandle(idx, true);
			if (!rmutex || !waitMutex(rmutex, false))
				ok = false;
		}
		if (!ok && rmutex) {
			CloseHandle(rmutex);
			rmutex = 0;
		}
		ReleaseMutex(wmutex);
		if (!ok)
			return false;
	}
	else {
		Q_ASSERT(rmutexes.isEmpty());
		for (int i = 0; i < MAX_READERS; i++) {
			Qt::HANDLE mutex = getMutexHandle(i, false);
			if (mutex)
				rmutexes.append(mutex);
		}
		if (rmutexes.size()) {
			DWORD res = WaitForMultipleObjects(rmutexes.size(), rmutexes.constData(),
											TRUE, block ? INFINITE : 0);
			if (res != WAIT_OBJECT_0 && res != WAIT_ABANDONED) {
				if (res != WAIT_TIMEOUT)
					qErrnoWarning("QtLockedFile::lock(): WaitForMultipleObjects failed");
				m_lock_mode = WriteLock;  // trick unlock() to clean up - semiyucky
				unlock();
				return false;
			}
		}
	}

	m_lock_mode = mode;
	return true;
}

bool LockedFile::unlock()
{
	if (!isOpen()) {
		qWarning("QtLockedFile::unlock(): file is not opened");
		return false;
	}

	if (!isLocked())
		return true;

	if (m_lock_mode == ReadLock) {
		ReleaseMutex(rmutex);
		CloseHandle(rmutex);
		rmutex = 0;
	}
	else {
		foreach(Qt::HANDLE mutex, rmutexes) {
			ReleaseMutex(mutex);
			CloseHandle(mutex);
		}
		rmutexes.clear();
		ReleaseMutex(wmutex);
	}

	m_lock_mode = LockedFile::NoLock;
	return true;
}

LockedFile::~LockedFile()
{
	if (isOpen())
		unlock();
	if (wmutex)
		CloseHandle(wmutex);
}