/****************************************************************************
**
** Copyright (C) 2015 The Qt Company Ltd.
** Contact: http://www.qt.io/licensing/
**
** This file is part of the QtCore module of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL21$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see http://www.qt.io/terms-conditions. For further
** information use the contact form at http://www.qt.io/contact-us.
**
** 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.
**
** As a special exception, The Qt Company gives you certain additional
** rights. These rights are described in The Qt Company LGPL Exception
** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
**
** $QT_END_LICENSE$
**
****************************************************************************/
#include "qeventloop.h"
#include "qabstracteventdispatcher.h"
#include "qcoreapplication.h"
#include "qcoreapplication_p.h"
#include "qelapsedtimer.h"
#include "qobject_p.h"
#include "qeventloop_p.h"
#include <private/qthread_p.h>
QT_BEGIN_NAMESPACE
/*!
\class QEventLoop
\inmodule QtCore
\brief The QEventLoop class provides a means of entering and leaving an event loop.
At any time, you can create a QEventLoop object and call exec()
on it to start a local event loop. From within the event loop,
calling exit() will force exec() to return.
\sa QAbstractEventDispatcher
*/
/*!
\enum QEventLoop::ProcessEventsFlag
This enum controls the types of events processed by the
processEvents() functions.
\value AllEvents All events. Note that
\l{QEvent::DeferredDelete}{DeferredDelete} events are processed
specially. See QObject::deleteLater() for more details.
\value ExcludeUserInputEvents Do not process user input events,
such as ButtonPress and KeyPress. Note that the events are not
discarded; they will be delivered the next time processEvents() is
called without the ExcludeUserInputEvents flag.
\value ExcludeSocketNotifiers Do not process socket notifier
events. Note that the events are not discarded; they will be
delivered the next time processEvents() is called without the
ExcludeSocketNotifiers flag.
\value WaitForMoreEvents Wait for events if no pending events are
available.
\omitvalue X11ExcludeTimers
\omitvalue EventLoopExec
\omitvalue DialogExec
\sa processEvents()
*/
/*!
Constructs an event loop object with the given \a parent.
*/
QEventLoop::QEventLoop(QObject *parent)
: QObject(*new QEventLoopPrivate, parent)
{
Q_D(QEventLoop);
if (!QCoreApplication::instance() && QCoreApplicationPrivate::threadRequiresCoreApplication()) {
qWarning("QEventLoop: Cannot be used without QApplication");
} else if (!d->threadData->eventDispatcher.load()) {
QThreadPrivate::createEventDispatcher(d->threadData);
}
}
/*!
Destroys the event loop object.
*/
QEventLoop::~QEventLoop()
{ }
/*!
Processes pending events that match \a flags until there are no
more events to process. Returns \c true if pending events were handled;
otherwise returns \c false.
This function is especially useful if you have a long running
operation and want to show its progress without allowing user
input; i.e. by using the \l ExcludeUserInputEvents flag.
This function is simply a wrapper for
QAbstractEventDispatcher::processEvents(). See the documentation
for that function for details.
*/
bool QEventLoop::processEvents(ProcessEventsFlags flags)
{
Q_D(QEventLoop);
if (!d->threadData->eventDispatcher.load())
return false;
return d->threadData->eventDispatcher.load()->processEvents(flags);
}
/*!
Enters the main event loop and waits until exit() is called.
Returns the value that was passed to exit().
If \a flags are specified, only events of the types allowed by
the \a flags will be processed.
It is necessary to call this function to start event handling. The
main event loop receives events from the window system and
dispatches these to the application widgets.
Generally speaking, no user interaction can take place before
calling exec(). As a special case, modal widgets like QMessageBox
can be used before calling exec(), because modal widgets
use their own local event loop.
To make your application perform idle processing (i.e. executing a
special function whenever there are no pending events), use a
QTimer with 0 timeout. More sophisticated idle processing schemes
can be achieved using processEvents().
\sa QCoreApplication::quit(), exit(), processEvents()
*/
int QEventLoop::exec(ProcessEventsFlags flags)
{
Q_D(QEventLoop);
//we need to protect from race condition with QThread::exit
QMutexLocker locker(&static_cast<QThreadPrivate *>(QObjectPrivate::get(d->threadData->thread))->mutex);
if (d->threadData->quitNow)
return -1;
if (d->inExec) {
qWarning("QEventLoop::exec: instance %p has already called exec()", this);
return -1;
}
struct LoopReference {
QEventLoopPrivate *d;
QMutexLocker &locker;
bool exceptionCaught;
LoopReference(QEventLoopPrivate *d, QMutexLocker &locker) : d(d), locker(locker), exceptionCaught(true)
{
d->inExec = true;
d->exit.storeRelease(false);
++d->threadData->loopLevel;
d->threadData->eventLoops.push(d->q_func());
locker.unlock();
}
~LoopReference()
{
if (exceptionCaught) {
qWarning("Qt has caught an exception thrown from an event handler. Throwing\n"
"exceptions from an event handler is not supported in Qt.\n"
"You must not let any exception whatsoever propagate through Qt code.\n"
"If that is not possible, in Qt 5 you must at least reimplement\n"
"QCoreApplication::notify() and catch all exceptions there.\n");
}
locker.relock();
QEventLoop *eventLoop = d->threadData->eventLoops.pop();
Q_ASSERT_X(eventLoop == d->q_func(), "QEventLoop::exec()", "internal error");
Q_UNUSED(eventLoop); // --release warning
d->inExec = false;
--d->threadData->loopLevel;
}
};
LoopReference ref(d, locker);
// remove posted quit events when entering a new event loop
QCoreApplication *app = QCoreApplication::instance();
if (app && app->thread() == thread())
QCoreApplication::removePostedEvents(app, QEvent::Quit);
while (!d->exit.loadAcquire())
processEvents(flags | WaitForMoreEvents | EventLoopExec);
ref.exceptionCaught = false;
return d->returnCode.load();
}
/*!
Process pending events that match \a flags for a maximum of \a
maxTime milliseconds, or until there are no more events to
process, whichever is shorter.
This function is especially useful if you have a long running
operation and want to show its progress without allowing user
input, i.e. by using the \l ExcludeUserInputEvents flag.
\b{Notes:}
\list
\li This function does not process events continuously; it
returns after all available events are processed.
\li Specifying the \l WaitForMoreEvents flag makes no sense
and will be ignored.
\endlist
*/
void QEventLoop::processEvents(ProcessEventsFlags flags, int maxTime)
{
Q_D(QEventLoop);
if (!d->threadData->eventDispatcher.load())
return;
QElapsedTimer start;
start.start();
while (processEvents(flags & ~WaitForMoreEvents)) {
if (start.elapsed() > maxTime)
break;
}
}
/*!
Tells the event loop to exit with a return code.
After this function has been called, the event loop returns from
the call to exec(). The exec() function returns \a returnCode.
By convention, a \a returnCode of 0 means success, and any non-zero
value indicates an error.
Note that unlike the C library function of the same name, this
function \e does return to the caller -- it is event processing that
stops.
\sa QCoreApplication::quit(), quit(), exec()
*/
void QEventLoop::exit(int returnCode)
{
Q_D(QEventLoop);
if (!d->threadData->eventDispatcher.load())
return;
d->returnCode.store(returnCode);
d->exit.storeRelease(true);
d->threadData->eventDispatcher.load()->interrupt();
}
/*!
Returns \c true if the event loop is running; otherwise returns
false. The event loop is considered running from the time when
exec() is called until exit() is called.
\sa exec(), exit()
*/
bool QEventLoop::isRunning() const
{
Q_D(const QEventLoop);
return !d->exit.loadAcquire();
}
/*!
Wakes up the event loop.
\sa QAbstractEventDispatcher::wakeUp()
*/
void QEventLoop::wakeUp()
{
Q_D(QEventLoop);
if (!d->threadData->eventDispatcher.load())
return;
d->threadData->eventDispatcher.load()->wakeUp();
}
/*!
\reimp
*/
bool QEventLoop::event(QEvent *event)
{
if (event->type() == QEvent::Quit) {
quit();
return true;
} else {
return QObject::event(event);
}
}
/*!
Tells the event loop to exit normally.
Same as exit(0).
\sa QCoreApplication::quit(), exit()
*/
void QEventLoop::quit()
{ exit(0); }
class QEventLoopLockerPrivate
{
public:
explicit QEventLoopLockerPrivate(QEventLoopPrivate *loop)
: loop(loop), type(EventLoop)
{
loop->ref();
}
explicit QEventLoopLockerPrivate(QThreadPrivate *thread)
: thread(thread), type(Thread)
{
thread->ref();
}
explicit QEventLoopLockerPrivate(QCoreApplicationPrivate *app)
: app(app), type(Application)
{
app->ref();
}
~QEventLoopLockerPrivate()
{
switch (type)
{
case EventLoop:
loop->deref();
break;
case Thread:
thread->deref();
break;
default:
app->deref();
break;
}
}
private:
union {
QEventLoopPrivate * loop;
QThreadPrivate * thread;
QCoreApplicationPrivate * app;
};
enum Type {
EventLoop,
Thread,
Application
};
const Type type;
};
/*!
\class QEventLoopLocker
\inmodule QtCore
\brief The QEventLoopLocker class provides a means to quit an event loop when it is no longer needed.
\since 5.0
The QEventLoopLocker operates on particular objects - either a QCoreApplication
instance, a QEventLoop instance or a QThread instance.
This makes it possible to, for example, run a batch of jobs with an event loop
and exit that event loop after the last job is finished. That is accomplished
by keeping a QEventLoopLocker with each job instance.
The variant which operates on QCoreApplication makes it possible to finish
asynchronously running jobs after the last gui window has been closed. This
can be useful for example for running a job which uploads data to a network.
\sa QEventLoop, QCoreApplication
*/
/*!
Creates an event locker operating on the QCoreApplication.
The application will quit when there are no more QEventLoopLockers operating on it.
\sa QCoreApplication::quit(), QCoreApplication::isQuitLockEnabled()
*/
QEventLoopLocker::QEventLoopLocker()
: d_ptr(new QEventLoopLockerPrivate(static_cast<QCoreApplicationPrivate*>(QObjectPrivate::get(QCoreApplication::instance()))))
{
}
/*!
Creates an event locker operating on the \a loop.
This particular QEventLoop will quit when there are no more QEventLoopLockers operating on it.
\sa QEventLoop::quit()
*/
QEventLoopLocker::QEventLoopLocker(QEventLoop *loop)
: d_ptr(new QEventLoopLockerPrivate(static_cast<QEventLoopPrivate*>(QObjectPrivate::get(loop))))
{
}
/*!
Creates an event locker operating on the \a thread.
This particular QThread will quit when there are no more QEventLoopLockers operating on it.
\sa QThread::quit()
*/
QEventLoopLocker::QEventLoopLocker(QThread *thread)
: d_ptr(new QEventLoopLockerPrivate(static_cast<QThreadPrivate*>(QObjectPrivate::get(thread))))
{
}
/*!
Destroys this event loop locker object
*/
QEventLoopLocker::~QEventLoopLocker()
{
delete d_ptr;
}
QT_END_NAMESPACE
参考：
https://www.yuque.com/docs/share/ab6d4575-7b38-45c2-8316-391a444d53c5
