Question

在这里提出这个问题之前，我已经想了很多并阅读了很多文章。这些文章都没有给我一个正确的答案。

http://mayaposch.wordpress.com/2011/11/01/how-to-really-truly-use-qthreads-the-full-explanation/

 QThread* thread = new QThread;
 Worker* worker = new Worker();
 worker->moveToThread(thread);
 connect(worker, SIGNAL(error(QString)), this, SLOT(errorString(QString)));
 connect(thread, SIGNAL(started()), worker, SLOT(process()));
 connect(worker, SIGNAL(finished()), thread, SLOT(quit()));
 connect(worker, SIGNAL(finished()), worker, SLOT(deleteLater()));
 connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()));
 thread->start();

Worker对象具有新线程的亲和力。

1＆gt; Worker完成信号将调用线程上的quit（）。这将结束线程的事件循环并启动线程完成信号。

2＆gt; Worker finished信号连接到worker deleteLater（）。根据deleteLater（）文档

**安排此对象删除。   当控制返回到事件循环时，将删除该对象。如果事件循环是>没有跑

调用此函数时（例如，在调用deleteLater（）时）   在QCoreApplication :: exec（）之前的对象，该对象将被删除   一旦事件循环开始。

注意进入和离开新的   事件循环（例如，通过打开模态对话框）将不执行   延期删除;对于要删除的对象，控件必须   返回调用deleteLater（）的事件循环。

注意：它   可以安全地多次调用此函数;当第一个推迟   删除事件已传递，该对象的任何待处理事件都是   从事件队列中删除。**

因此，当没有eventloop时，因为线程已经退出并且它已经提出了已完成的信号，我们将不再再次启动相同的线程。在这种情况下，将永远不会处理deleteLater（），因为事件循环不存在，并且根本不会删除worker对象。这不会造成内存泄漏吗？

 connect(worker, SIGNAL(finished()), worker, SLOT(deleteLater()));
 connect(worker, SIGNAL(finished()), thread, SLOT(quit()));

如果我们认为交换这两行将解决问题，那么我还有另外一个问题。 QT明确指出，在发出信号时调用插槽的顺序是不确定的

上面提到的文章链接中有很多评论。甚至作者也无法完全回答这个问题

Answer 1

QThread在发送完成信号后会执行事件类型为QEvent :: DeferredDelete的QCoreApplication::sendPostedEvents

换句话说，QThread将收集所有挂起的deleteLaters并在run返回后执行它们

来源：https://qt.gitorious.org/qt/qtbase/source/c657bb7b51115d6e1719166fb502bb0ca1dcf4e8:src/corelib/thread/qthread_win.cpp#L363-462

Answer 2

//! put the following code in constructor
QThread *thread = new QThread;
//! type of m_weakThread is QWeakPointer<QThread>
m_weakThread = thread;
Worker *worker = new Worker;
//! type of m_weakWorker is QWeakPointer<Worker>
m_weakWorker = worker;
worker->moveToThread(thread);
connect(worker, SIGNAL(error(QString)), this, SLOT(errorString(QString)));
connect(thread, SIGNAL(started()), worker, SLOT(process()));
connect(worker, SIGNAL(finished()), worker, SLOT(deleteLater()));
//! instead of finished() signal, connect destroyed() signal to thread's quit() slot
connect(worker, SIGNAL(destroyed()), thread, SLOT(quit()));
connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()));
thread->start();

//! put the following code in destructor
if (!m_weakThread.isNull()) {
    QThread *thread = m_weakThread.data();
    if (thread->isRunning()) {
        thread->quit();
        thread->wait();
    }
}
if (!m_weakWorker.isNull()) {
    Worker *worker = m_weakWorker.data();
    m_weakWorker.clear();   //! optional, a little optimization
    //! it's safe to release worker since the secondary thread exits
    delete worker;
}
if (!m_weakThread.isNull()) {
    QThread *thread = m_weakThread.data();
    m_weakThread.clear();
    //! it's safe to release thread since it exits and all objects in it has released
    delete thread;
}

完成（）连接到QObject的deletelater的QThread

2 个答案: