72ecf5a7ec
First step to fix race condition about deleting QDBusPendingCallPrivate.
In a multithreaded application on a slow/single core cpu the following
race (and segmentation fault) can occur:
First thread A is running:
A: QDBusPendingReply<> reply = pi->asyncCallWithArgumentList(method, argumentList);
Then when the dbus answer arrives thread B will call:
B: QDBusConnectionPrivate::processFinishedCall()
B: ...
B: locker.unlock()
and runs until here, go on with thread A:
A: reply.waitForFinished();
A: QDBusPendingCallPrivate::waitForFinished()
A: {
A: QMutexLocker locker(&mutex);
A: if (replyMessage.type() != QDBusMessage::InvalidMessage)
A: return;
which returns immediately (mutex acquired, replyMessage alread set), now
reply goes out of scope (destructor called) and QDBusPendingCall::d's
destructor of type QExplicitlySharedDataPointer<QDBusPendingCallPrivate>
deletes the reference counted object QDBusPendingCallPrivate.
Now thread B continues, still in processFinishedCall()
B: if (call->watcherHelper)
B: call->watcherHelper->emitSignals(msg, call->sentMessage);
B:
B: if (msg.type() == QDBusMessage::ErrorMessage)
B: emit connection->callWithCallbackFailed(QDBusError(msg),
B: call->sentMessage);
accessing alread deleted object QDBusPendingCallPrivate via call->...
Fixed QDBusPendingCallPrivate deletion by proper reference counting
will be done in the next commit.
Task-number: QTBUG-27809
Change-Id: I15b3f0242471b62eaafadc763fb6a33339ff2fe1
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
140 lines
4.3 KiB
C++
140 lines
4.3 KiB
C++
/****************************************************************************
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**
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** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
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** Contact: http://www.qt-project.org/legal
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**
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** This file is part of the QtDBus module of the Qt Toolkit.
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**
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** $QT_BEGIN_LICENSE:LGPL$
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** Commercial License Usage
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** Licensees holding valid commercial Qt licenses may use this file in
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** accordance with the commercial license agreement provided with the
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** Software or, alternatively, in accordance with the terms contained in
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** a written agreement between you and Digia. For licensing terms and
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** conditions see http://qt.digia.com/licensing. For further information
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** use the contact form at http://qt.digia.com/contact-us.
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**
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** GNU Lesser General Public License Usage
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** Alternatively, this file may be used under the terms of the GNU Lesser
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** General Public License version 2.1 as published by the Free Software
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** Foundation and appearing in the file LICENSE.LGPL included in the
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** packaging of this file. Please review the following information to
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** ensure the GNU Lesser General Public License version 2.1 requirements
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** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
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**
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** In addition, as a special exception, Digia gives you certain additional
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** rights. These rights are described in the Digia Qt LGPL Exception
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** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
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**
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** GNU General Public License Usage
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** Alternatively, this file may be used under the terms of the GNU
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** General Public License version 3.0 as published by the Free Software
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** Foundation and appearing in the file LICENSE.GPL included in the
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** packaging of this file. Please review the following information to
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** ensure the GNU General Public License version 3.0 requirements will be
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** met: http://www.gnu.org/copyleft/gpl.html.
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**
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**
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** $QT_END_LICENSE$
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**
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****************************************************************************/
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//
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// W A R N I N G
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// -------------
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//
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// This file is not part of the public API. This header file may
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// change from version to version without notice, or even be
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// removed.
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//
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// We mean it.
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//
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//
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#ifndef QDBUSPENDINGCALL_P_H
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#define QDBUSPENDINGCALL_P_H
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#include <qshareddata.h>
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#include <qpointer.h>
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#include <qvector.h>
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#include <qmutex.h>
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#include <qwaitcondition.h>
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#include "qdbusmessage.h"
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#include "qdbus_symbols_p.h"
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#ifndef QT_NO_DBUS
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QT_BEGIN_NAMESPACE
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class QDBusPendingCall;
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class QDBusPendingCallWatcher;
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class QDBusPendingCallWatcherHelper;
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class QDBusConnectionPrivate;
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class QDBusPendingCallPrivate: public QSharedData
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{
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public:
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// {
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// set only during construction:
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const QDBusMessage sentMessage;
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QDBusConnectionPrivate * const connection;
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// for the callback mechanism (see setReplyCallback and QDBusConnectionPrivate::sendWithReplyAsync)
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QPointer<QObject> receiver;
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QVector<int> metaTypes;
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int methodIdx;
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// }
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mutable QMutex mutex;
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QWaitCondition waitForFinishedCondition;
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// {
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// protected by the mutex above:
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QDBusPendingCallWatcherHelper *watcherHelper;
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QDBusMessage replyMessage;
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DBusPendingCall *pending;
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QString expectedReplySignature;
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int expectedReplyCount;
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bool waitingForFinished;
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// }
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QDBusPendingCallPrivate(const QDBusMessage &sent, QDBusConnectionPrivate *connection)
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: sentMessage(sent), connection(connection), watcherHelper(0), pending(0), waitingForFinished(false)
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{ }
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~QDBusPendingCallPrivate();
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bool setReplyCallback(QObject *target, const char *member);
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void waitForFinished();
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void setMetaTypes(int count, const int *types);
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void checkReceivedSignature();
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static QDBusPendingCall fromMessage(const QDBusMessage &msg);
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};
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class QDBusPendingCallWatcherHelper: public QObject
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{
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Q_OBJECT
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public:
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void add(QDBusPendingCallWatcher *watcher);
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void emitSignals(const QDBusMessage &replyMessage, const QDBusMessage &sentMessage)
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{
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if (replyMessage.type() == QDBusMessage::ReplyMessage)
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emit reply(replyMessage);
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else
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emit error(QDBusError(replyMessage), sentMessage);
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emit finished();
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}
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Q_SIGNALS:
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void finished();
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void reply(const QDBusMessage &msg);
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void error(const QDBusError &error, const QDBusMessage &msg);
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};
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QT_END_NAMESPACE
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#endif // QT_NO_DBUS
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#endif
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