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QLockFile was introduced in Qt 5.1.

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branch : develop
This commit is contained in:
Roman Telezhynskyi 2015-04-02 15:54:35 +03:00
parent 4d171184bd
commit 49ffd7a77d
6 changed files with 495 additions and 4 deletions
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7
src/app/core/core.pri
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@ -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

331
src/app/core/qlockfile.cpp Normal file
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@ -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)

66
src/app/core/qlockfile.h Normal file
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@ -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

83
src/app/core/qlockfile_p.h Normal file
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@ -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 */

6
src/app/core/vapplication.cpp
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@ -49,7 +49,11 @@
#include <QMessageBox>
#include <QThread>
#include <QDateTime>
#include <QLockFile>
#if QT_VERSION < QT_VERSION_CHECK(5, 1, 0)
# include "qlockfile.h"
#else
# include <QLockFile>
#endif
#include <QtXmlPatterns>
using namespace qmu;

6
src/app/mainwindow.cpp
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@ -61,7 +61,11 @@
#include <QtGlobal>
#include <QDesktopWidget>
#include <QDesktopServices>
#include <QLockFile>
#if QT_VERSION < QT_VERSION_CHECK(5, 1, 0)
# include "qlockfile.h"
#else
# include <QLockFile>
#endif
Q_LOGGING_CATEGORY(vMainWindow, "v.mainwindow")