QLockFile was introduced in Qt 5.1.

--HG--
branch : develop

src/app/core/core.pri

@@ -6,11 +6,14 @@ HEADERS += \
     $$PWD/undoevent.h \
     $$PWD/vsettings.h \
     $$PWD/qcommandlineoption.h \
-    $$PWD/qcommandlineparser.h
+    $$PWD/qcommandlineparser.h \
+    $$PWD/qlockfile.h \
+    $$PWD/qlockfile_p.h
 
 SOURCES += \
     $$PWD/vapplication.cpp \
     $$PWD/undoevent.cpp \
     $$PWD/vsettings.cpp \
     $$PWD/qcommandlineoption.cpp \
-    $$PWD/qcommandlineparser.cpp
+    $$PWD/qcommandlineparser.cpp \
+    $$PWD/qlockfile.cpp

src/app/core/qlockfile.cpp

@@ -0,0 +1,331 @@
+/****************************************************************************
+**
+** Copyright (C) 2013 David Faure <faure+bluesystems@kde.org>
+** Contact: http://www.qt-project.org/legal
+**
+** $QT_BEGIN_LICENSE:GPL$
+**
+** 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.
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qlockfile.h"
+#include "qlockfile_p.h"
+
+#include <QThread>
+#include <QElapsedTimer>
+#include <QDateTime>
+
+#if QT_VERSION < QT_VERSION_CHECK(5, 1, 0)
+
+class QLockFileThread : public QThread
+{
+public:
+    static void msleep(unsigned long msecs) { QThread::msleep(msecs); }
+};
+
+/*!
+    \class QLockFile
+    \inmodule QtCore
+    \brief The QLockFile class provides locking between processes using a file.
+    \since 5.1
+
+    A lock file can be used to prevent multiple processes from accessing concurrently
+    the same resource. For instance, a configuration file on disk, or a socket, a port,
+    a region of shared memory...
+
+    Serialization is only guaranteed if all processes that access the shared resource
+    use QLockFile, with the same file path.
+
+    QLockFile supports two use cases:
+    to protect a resource for a short-term operation (e.g. verifying if a configuration
+    file has changed before saving new settings), and for long-lived protection of a
+    resource (e.g. a document opened by a user in an editor) for an indefinite amount of time.
+
+    When protecting for a short-term operation, it is acceptable to call lock() and wait
+    until any running operation finishes.
+    When protecting a resource over a long time, however, the application should always
+    call setStaleLockTime(0) and then tryLock() with a short timeout, in order to
+    warn the user that the resource is locked.
+
+    If the process holding the lock crashes, the lock file stays on disk and can prevent
+    any other process from accessing the shared resource, ever. For this reason, QLockFile
+    tries to detect such a "stale" lock file, based on the process ID written into the file,
+    and (in case that process ID got reused meanwhile), on the last modification time of
+    the lock file (30s by default, for the use case of a short-lived operation).
+    If the lock file is found to be stale, it will be deleted.
+
+    For the use case of protecting a resource over a long time, you should therefore call
+    setStaleLockTime(0), and when tryLock() returns LockFailedError, inform the user
+    that the document is locked, possibly using getLockInfo() for more details.
+*/
+
+/*!
+    \enum QLockFile::LockError
+
+    This enum describes the result of the last call to lock() or tryLock().
+
+    \value NoError The lock was acquired successfully.
+    \value LockFailedError The lock could not be acquired because another process holds it.
+    \value PermissionError The lock file could not be created, for lack of permissions
+                           in the parent directory.
+    \value UnknownError Another error happened, for instance a full partition
+                        prevented writing out the lock file.
+*/
+
+/*!
+    Constructs a new lock file object.
+    The object is created in an unlocked state.
+    When calling lock() or tryLock(), a lock file named \a fileName will be created,
+    if it doesn't already exist.
+
+    \sa lock(), unlock()
+*/
+QLockFile::QLockFile(const QString &fileName)
+    : d_ptr(new QLockFilePrivate(fileName))
+{
+}
+
+/*!
+    Destroys the lock file object.
+    If the lock was acquired, this will release the lock, by deleting the lock file.
+*/
+QLockFile::~QLockFile()
+{
+    unlock();
+}
+
+/*!
+    Sets \a staleLockTime to be the time in milliseconds after which
+    a lock file is considered stale.
+    The default value is 30000, i.e. 30 seconds.
+    If your application typically keeps the file locked for more than 30 seconds
+    (for instance while saving megabytes of data for 2 minutes), you should set
+    a bigger value using setStaleLockTime().
+
+    The value of \a staleLockTime is used by lock() and tryLock() in order
+    to determine when an existing lock file is considered stale, i.e. left over
+    by a crashed process. This is useful for the case where the PID got reused
+    meanwhile, so the only way to detect a stale lock file is by the fact that
+    it has been around for a long time.
+
+    \sa staleLockTime()
+*/
+void QLockFile::setStaleLockTime(int staleLockTime)
+{
+    Q_D(QLockFile);
+    d->staleLockTime = staleLockTime;
+}
+
+/*!
+    Returns the time in milliseconds after which
+    a lock file is considered stale.
+
+    \sa setStaleLockTime()
+*/
+int QLockFile::staleLockTime() const
+{
+    Q_D(const QLockFile);
+    return d->staleLockTime;
+}
+
+/*!
+    Returns \c true if the lock was acquired by this QLockFile instance,
+    otherwise returns \c false.
+
+    \sa lock(), unlock(), tryLock()
+*/
+bool QLockFile::isLocked() const
+{
+    Q_D(const QLockFile);
+    return d->isLocked;
+}
+
+/*!
+    Creates the lock file.
+
+    If another process (or another thread) has created the lock file already,
+    this function will block until that process (or thread) releases it.
+
+    Calling this function multiple times on the same lock from the same
+    thread without unlocking first is not allowed. This function will
+    \e dead-lock when the file is locked recursively.
+
+    Returns \c true if the lock was acquired, false if it could not be acquired
+    due to an unrecoverable error, such as no permissions in the parent directory.
+
+    \sa unlock(), tryLock()
+*/
+bool QLockFile::lock()
+{
+    return tryLock(-1);
+}
+
+/*!
+    Attempts to create the lock file. This function returns \c true if the
+    lock was obtained; otherwise it returns \c false. If another process (or
+    another thread) has created the lock file already, this function will
+    wait for at most \a timeout milliseconds for the lock file to become
+    available.
+
+    Note: Passing a negative number as the \a timeout is equivalent to
+    calling lock(), i.e. this function will wait forever until the lock
+    file can be locked if \a timeout is negative.
+
+    If the lock was obtained, it must be released with unlock()
+    before another process (or thread) can successfully lock it.
+
+    Calling this function multiple times on the same lock from the same
+    thread without unlocking first is not allowed, this function will
+    \e always return false when attempting to lock the file recursively.
+
+    \sa lock(), unlock()
+*/
+bool QLockFile::tryLock(int timeout)
+{
+    Q_D(QLockFile);
+    QElapsedTimer timer;
+    if (timeout > 0)
+        timer.start();
+    int sleepTime = 100;
+    forever {
+        d->lockError = d->tryLock_sys();
+        switch (d->lockError) {
+        case NoError:
+            d->isLocked = true;
+            return true;
+        case PermissionError:
+        case UnknownError:
+            return false;
+        case LockFailedError:
+            if (!d->isLocked && d->isApparentlyStale()) {
+                // Stale lock from another thread/process
+                // Ensure two processes don't remove it at the same time
+                QLockFile rmlock(d->fileName + QLatin1String(".rmlock"));
+                if (rmlock.tryLock()) {
+                    if (d->isApparentlyStale() && d->removeStaleLock())
+                        continue;
+                }
+            }
+            break;
+        }
+        if (timeout == 0 || (timeout > 0 && timer.hasExpired(timeout)))
+            return false;
+        QLockFileThread::msleep(sleepTime);
+        if (sleepTime < 5 * 1000)
+            sleepTime *= 2;
+    }
+    // not reached
+    return false;
+}
+
+/*!
+    \fn void QLockFile::unlock()
+    Releases the lock, by deleting the lock file.
+
+    Calling unlock() without locking the file first, does nothing.
+
+    \sa lock(), tryLock()
+*/
+
+/*!
+    Retrieves information about the current owner of the lock file.
+
+    If tryLock() returns \c false, and error() returns LockFailedError,
+    this function can be called to find out more information about the existing
+    lock file:
+    \list
+    \li the PID of the application (returned in \a pid)
+    \li the \a hostname it's running on (useful in case of networked filesystems),
+    \li the name of the application which created it (returned in \a appname),
+    \endlist
+
+    Note that tryLock() automatically deleted the file if there is no
+    running application with this PID, so LockFailedError can only happen if there is
+    an application with this PID (it could be unrelated though).
+
+    This can be used to inform users about the existing lock file and give them
+    the choice to delete it. After removing the file using removeStaleLockFile(),
+    the application can call tryLock() again.
+
+    This function returns \c true if the information could be successfully retrieved, false
+    if the lock file doesn't exist or doesn't contain the expected data.
+    This can happen if the lock file was deleted between the time where tryLock() failed
+    and the call to this function. Simply call tryLock() again if this happens.
+*/
+bool QLockFile::getLockInfo(qint64 *pid, QString *hostname, QString *appname) const
+{
+    Q_D(const QLockFile);
+    return d->getLockInfo(pid, hostname, appname);
+}
+
+bool QLockFilePrivate::getLockInfo(qint64 *pid, QString *hostname, QString *appname) const
+{
+    QFile reader(fileName);
+    if (!reader.open(QIODevice::ReadOnly))
+        return false;
+
+    QByteArray pidLine = reader.readLine();
+    pidLine.chop(1);
+    QByteArray appNameLine = reader.readLine();
+    appNameLine.chop(1);
+    QByteArray hostNameLine = reader.readLine();
+    hostNameLine.chop(1);
+    if (pidLine.isEmpty() || appNameLine.isEmpty())
+        return false;
+
+    qint64 thePid = pidLine.toLongLong();
+    if (pid)
+        *pid = thePid;
+    if (appname)
+        *appname = QString::fromUtf8(appNameLine);
+    if (hostname)
+        *hostname = QString::fromUtf8(hostNameLine);
+    return thePid > 0;
+}
+
+/*!
+    Attempts to forcefully remove an existing lock file.
+
+    Calling this is not recommended when protecting a short-lived operation: QLockFile
+    already takes care of removing lock files after they are older than staleLockTime().
+
+    This method should only be called when protecting a resource for a long time, i.e.
+    with staleLockTime(0), and after tryLock() returned LockFailedError, and the user
+    agreed on removing the lock file.
+
+    Returns \c true on success, false if the lock file couldn't be removed. This happens
+    on Windows, when the application owning the lock is still running.
+*/
+bool QLockFile::removeStaleLockFile()
+{
+    Q_D(QLockFile);
+    if (d->isLocked) {
+        qWarning("removeStaleLockFile can only be called when not holding the lock");
+        return false;
+    }
+    return d->removeStaleLock();
+}
+
+/*!
+    Returns the lock file error status.
+
+    If tryLock() returns \c false, this function can be called to find out
+    the reason why the locking failed.
+*/
+QLockFile::LockError QLockFile::error() const
+{
+    Q_D(const QLockFile);
+    return d->lockError;
+}
+
+#endif //QT_VERSION < QT_VERSION_CHECK(5, 1, 0)

src/app/core/qlockfile.h

@@ -0,0 +1,66 @@
+/****************************************************************************
+**
+** Copyright (C) 2013 David Faure <faure+bluesystems@kde.org>
+** Contact: http://www.qt-project.org/legal
+**
+** $QT_BEGIN_LICENSE:LGPL21$
+**
+** 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 or version 3 as published by the Free
+** Software Foundation and appearing in the file LICENSE.LGPLv21 and
+** LICENSE.LGPLv3 included in the packaging of this file. Please review the
+** following information to ensure the GNU Lesser General Public License
+** requirements will be met: https://www.gnu.org/licenses/lgpl.html and
+** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QLOCKFILE_H
+#define QLOCKFILE_H
+
+#include <QString>
+#include <QScopedPointer>
+
+#if QT_VERSION < QT_VERSION_CHECK(5, 1, 0)
+
+class QLockFilePrivate;
+
+class QLockFile
+{
+public:
+    QLockFile(const QString &fileName);
+    ~QLockFile();
+
+    bool lock();
+    bool tryLock(int timeout = 0);
+    void unlock();
+
+    void setStaleLockTime(int);
+    int staleLockTime() const;
+
+    bool isLocked() const;
+    bool getLockInfo(qint64 *pid, QString *hostname, QString *appname) const;
+    bool removeStaleLockFile();
+
+    enum LockError {
+        NoError = 0,
+        LockFailedError = 1,
+        PermissionError = 2,
+        UnknownError = 3
+    };
+    LockError error() const;
+
+protected:
+    QScopedPointer<QLockFilePrivate> d_ptr;
+
+private:
+    Q_DECLARE_PRIVATE(QLockFile)
+    Q_DISABLE_COPY(QLockFile)
+};
+
+#endif //QT_VERSION < QT_VERSION_CHECK(5, 1, 0)
+
+#endif // QLOCKFILE_H

src/app/core/qlockfile_p.h

@@ -0,0 +1,83 @@
+/****************************************************************************
+**
+** Copyright (C) 2013 David Faure <faure+bluesystems@kde.org>
+** Contact: http://www.qt-project.org/legal
+**
+** $QT_BEGIN_LICENSE:LGPL21$
+**
+** 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 or version 3 as published by the Free
+** Software Foundation and appearing in the file LICENSE.LGPLv21 and
+** LICENSE.LGPLv3 included in the packaging of this file. Please review the
+** following information to ensure the GNU Lesser General Public License
+** requirements will be met: https://www.gnu.org/licenses/lgpl.html and
+** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QLOCKFILE_P_H
+#define QLOCKFILE_P_H
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API.  It exists purely as an
+// implementation detail.  This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
+#include "qlockfile.h"
+#include <QFile>
+
+#ifdef Q_OS_WIN
+#include <qt_windows.h>
+#endif
+
+#if QT_VERSION < QT_VERSION_CHECK(5, 1, 0)
+
+class QLockFilePrivate
+{
+public:
+    QLockFilePrivate(const QString &fn)
+        : fileName(fn),
+#ifdef Q_OS_WIN
+          fileHandle(INVALID_HANDLE_VALUE),
+#else
+          fileHandle(-1),
+#endif
+          staleLockTime(30 * 1000), // 30 seconds
+          lockError(QLockFile::NoError),
+          isLocked(false)
+    {
+    }
+    QLockFile::LockError tryLock_sys();
+    bool removeStaleLock();
+    bool getLockInfo(qint64 *pid, QString *hostname, QString *appname) const;
+    // Returns \c true if the lock belongs to dead PID, or is old.
+    // The attempt to delete it will tell us if it was really stale or not, though.
+    bool isApparentlyStale() const;
+
+#ifdef Q_OS_UNIX
+    static int checkFcntlWorksAfterFlock();
+#endif
+
+    QString fileName;
+#ifdef Q_OS_WIN
+    Qt::HANDLE fileHandle;
+#else
+    int fileHandle;
+#endif
+    int staleLockTime; // "int milliseconds" is big enough for 24 days
+    QLockFile::LockError lockError;
+    bool isLocked;
+};
+
+#endif //QT_VERSION < QT_VERSION_CHECK(5, 1, 0)
+
+#endif /* QLOCKFILE_P_H */

src/app/core/vapplication.cpp

@@ -49,7 +49,11 @@
 #include <QMessageBox>
 #include <QThread>
 #include <QDateTime>
+#if QT_VERSION < QT_VERSION_CHECK(5, 1, 0)
+#   include "qlockfile.h"
+#else
 #   include <QLockFile>
+#endif
 #include <QtXmlPatterns>
 
 using namespace qmu;

src/app/mainwindow.cpp

@@ -61,7 +61,11 @@
 #include <QtGlobal>
 #include <QDesktopWidget>
 #include <QDesktopServices>
+#if QT_VERSION < QT_VERSION_CHECK(5, 1, 0)
+#   include "qlockfile.h"
+#else
 #   include <QLockFile>
+#endif
 
 Q_LOGGING_CATEGORY(vMainWindow, "v.mainwindow")