Fix race condition allowing to run several instances of qBittorrent at the same time

src/qtsingleapp/qtlockedfile_win.cpp

@@ -0,0 +1,213 @@
+/****************************************************************************
+** 
+** Copyright (c) 2009 Nokia Corporation and/or its subsidiary(-ies).
+** All rights reserved.
+** Contact: Nokia Corporation (qt-info@nokia.com)
+** 
+** This file is part of a Qt Solutions component.
+**
+** Commercial Usage  
+** Licensees holding valid Qt Commercial licenses may use this file in
+** accordance with the Qt Solutions Commercial License Agreement provided
+** with the Software or, alternatively, in accordance with the terms
+** contained in a written agreement between you and Nokia.
+** 
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 2.1 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU Lesser General Public License version 2.1 requirements
+** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+** 
+** In addition, as a special exception, Nokia gives you certain
+** additional rights. These rights are described in the Nokia Qt LGPL
+** Exception version 1.1, included in the file LGPL_EXCEPTION.txt in this
+** package.
+** 
+** GNU General Public License Usage 
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3.0 as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU General Public License version 3.0 requirements will be
+** met: http://www.gnu.org/copyleft/gpl.html.
+** 
+** Please note Third Party Software included with Qt Solutions may impose
+** additional restrictions and it is the user's responsibility to ensure
+** that they have met the licensing requirements of the GPL, LGPL, or Qt
+** Solutions Commercial license and the relevant license of the Third
+** Party Software they are using.
+** 
+** If you are unsure which license is appropriate for your use, please
+** contact Nokia at qt-info@nokia.com.
+** 
+****************************************************************************/
+
+#include "qtlockedfile.h"
+#include <qt_windows.h>
+#include <QtCore/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 QtLockedFile::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) {
+        QT_WA( { mutex = CreateMutexW(NULL, FALSE, (TCHAR*)mname.utf16()); },
+               { mutex = CreateMutexA(NULL, FALSE, mname.toLocal8Bit().constData()); } );
+        if (!mutex) {
+            qErrnoWarning("QtLockedFile::lock(): CreateMutex failed");
+            return 0;
+        }
+    }
+    else {
+        QT_WA( { mutex = OpenMutexW(SYNCHRONIZE | MUTEX_MODIFY_STATE, FALSE, (TCHAR*)mname.utf16()); },
+               { mutex = OpenMutexA(SYNCHRONIZE | MUTEX_MODIFY_STATE, FALSE, mname.toLocal8Bit().constData()); } );
+        if (!mutex) {
+            if (GetLastError() != ERROR_FILE_NOT_FOUND)
+                qErrnoWarning("QtLockedFile::lock(): OpenMutex failed");
+            return 0;
+        }
+    }
+    return mutex;
+}
+
+bool QtLockedFile::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 QtLockedFile::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 QtLockedFile::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 = QtLockedFile::NoLock;
+    return true;
+}
+
+QtLockedFile::~QtLockedFile()
+{
+    if (isOpen())
+        unlock();
+    if (wmutex)
+        CloseHandle(wmutex);
+}