如何防止对象无线程时出现QBasicTimer::stop: Failed警告？
如何防止对象无线程时出现QBasicTimer::stop: Failed警告？
提问于 2018-06-01 12:24:11
当QObject的工作线程在它们之前完成时，它们很容易变得无线程。当这种情况发生时，Qt不会释放它们的计时器ids，即使计时器不再处于活动状态。因此，将出现QBasicTimer::stop: Failed. Possibly trying to stop from a different thread警告。它主要是表面上的结果，但确实表明计时器id泄漏，因此有一个解决办法将是很好的。下面的示例触发问题：
#include <QtCore>
int main(int argc, char *argv[]) {
static_assert(QT_VERSION < QT_VERSION_CHECK(5,11,0), "");
QCoreApplication app(argc, argv);
QObject object;
object.startTimer(1000);
QThread workThread;
workThread.start();
object.moveToThread(&workThread);
QTimer::singleShot(500, &QCoreApplication::quit);
app.exec();
workThread.quit();
workThread.wait();
}如果解决方法不需要对计时器的分配方式进行任何修改，那就太好了，也就是说，除了Qt已经做的事情之外，不需要对计时器进行额外的跟踪。
回答 3
Stack Overflow用户
发布于 2018-06-01 13:08:27
一个简单的解决方案是防止这个问题:如果对象即将变得无线程，将其移动到线程句柄的父线程，然后当线程本身即将被析构时，重新建立对象的计时器以防止警告。
QObject的moveToThread实现有两个部分：
-
QEvent::ThreadChange从moveToThread传递给对象。QObject::event使用此事件来捕获和停用对象上活动的计时器。 - 目标线程中的事件循环将元调用传递给对象，
_q_reregisterTimers在新线程中运行，定时器在新线程中重新激活。请注意，如果_q_reregisterTimers没有机会运行，它将不可避免地泄漏计时器list.
因此，我们需要：
- 捕获对象即将变得无线程的时刻，并将其移动到另一个线程，这样
QMetaCallEventto_q_reactivateTimers就不会在正确的线程中触发事件。
因此：
// https://github.com/KubaO/stackoverflown/tree/master/questions/qbasictimer-stop-fix-50636079
#include <QtCore>
class Thread final : public QThread {
Q_OBJECT
void run() override {
connect(QAbstractEventDispatcher::instance(this),
&QAbstractEventDispatcher::aboutToBlock,
this, &Thread::aboutToBlock);
QThread::run();
}
QAtomicInt inDestructor;
public:
using QThread::QThread;
/// Take an object and prevent timer resource leaks when the object is about
/// to become threadless.
void takeObject(QObject *obj) {
// Work around to prevent
// QBasicTimer::stop: Failed. Possibly trying to stop from a different thread
static constexpr char kRegistered[] = "__ThreadRegistered";
static constexpr char kMoved[] = "__Moved";
if (!obj->property(kRegistered).isValid()) {
QObject::connect(this, &Thread::finished, obj, [this, obj]{
if (!inDestructor.load() || obj->thread() != this)
return;
// The object is about to become threadless
Q_ASSERT(obj->thread() == QThread::currentThread());
obj->setProperty(kMoved, true);
obj->moveToThread(this->thread());
}, Qt::DirectConnection);
QObject::connect(this, &QObject::destroyed, obj, [obj]{
if (!obj->thread()) {
obj->moveToThread(QThread::currentThread());
obj->setProperty(kRegistered, {});
}
else if (obj->thread() == QThread::currentThread() && obj->property(kMoved).isValid()) {
obj->setProperty(kMoved, {});
QCoreApplication::sendPostedEvents(obj, QEvent::MetaCall);
}
else if (obj->thread()->eventDispatcher())
QTimer::singleShot(0, obj, [obj]{ obj->setProperty(kRegistered, {}); });
}, Qt::DirectConnection);
obj->setProperty(kRegistered, true);
}
obj->moveToThread(this);
}
~Thread() override {
inDestructor.store(1);
requestInterruption();
quit();
wait();
}
Q_SIGNAL void aboutToBlock();
};
int main(int argc, char *argv[]) {
static_assert(QT_VERSION < QT_VERSION_CHECK(5,11,0), "");
QCoreApplication app(argc, argv);
QObject object1, object2;
object1.startTimer(10);
object2.startTimer(200);
Thread workThread1, workThread2;
QTimer::singleShot(500, &QCoreApplication::quit);
workThread1.start();
workThread2.start();
workThread1.takeObject(&object1);
workThread2.takeObject(&object2);
app.exec();
}
#include "main.moc"这种方法也可以很容易地扩展到动态跟踪obj的所有子对象: Qt提供了足够的事件来进行这样的跟踪。
Stack Overflow用户
发布于 2018-06-01 13:06:09
int id = object.startTimer(1000);
QThread workThread;
workThread.start();
object.moveToThread(&workThread);
QTimer::singleShot(500, &QCoreApplication::quit);
QObject::connect(&workThread, &QThread::finished, [&](){object.killTimer(id);});
...Stack Overflow用户
发布于 2018-06-01 17:35:23
如何将对象移回主线程...
class Object : public QObject
{
public:
using QObject::QObject;
virtual ~Object() {
qDebug()<<"Object"<<QThread::currentThread()<<this->thread();
if(thread() == Q_NULLPTR)
moveToThread(QThread::currentThread());
}
};
#include <QtCore>
int main(int argc, char *argv[]) {
static_assert(QT_VERSION < QT_VERSION_CHECK(5,11,0), "");
QCoreApplication app(argc, argv);
Object object;
object.startTimer(1000);
QThread workThread;
workThread.start();
object.moveToThread(&workThread);
QTimer::singleShot(500, &QCoreApplication::quit);
qDebug()<<"main"<<QThread::currentThread()<<object.thread();
app.exec();
workThread.quit();
workThread.wait();
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/50636079
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