为什么不调用此类的析构函数？

Question

我有两个类 - 一个在主线程中运行并执行GUI操作,另一个执行一些计算并发出网络请求.

// A member of the class that runs in the main thread
QThread thread;

这是在主线程中运行的类的初始化方法的片段:

// Create the class that runs in the other thread and move it there
CServerThread * server = new CServerThread;
server->moveToThread(&thread);

// When the thread terminates, we want the object destroyed
connect(&thread, SIGNAL(finished()), server, SLOT(deleteLater()));
thread.start();

在主线程中运行的类的析构函数中:

if(thread.isRunning())
{
    thread.quit();
    thread.wait();
}

我期望发生的是线程终止并销毁CServerThread类的实例.但是,CServerThread不会调用该类的析构函数.

Answer 1

QThread::quit() 停止该线程的事件循环.

告诉线程的事件循环退出并返回代码0(成功).

但是QObject::deleteLater()需要"拥有"线程的事件循环才能激活:

安排此对象进行删除.
当控制返回到事件循环时,将删除该对象.

所以你的对象的析构函数不会运行,因此finished发出的信号太迟了.

考虑下面的人为例子:

#include <QThread>
#include <iostream>

class T: public QObject
{
    Q_OBJECT

    public:
        QThread thr;
        T() {
            connect(&thr, SIGNAL(finished()), this, SLOT(finished()));
        };
        void start() {
            thr.start();
            std::cout << "Started" << std::endl;
        }
        void stop() {
            thr.quit();
            std::cout << "Has quit" << std::endl;
        }
        void end() {
            thr.wait();
            std::cout << "Done waiting" << std::endl;
        }
    public slots:
        void finished() {
            std::cout << "Finished" << std::endl;
        }
};

如果你打电话:

T t;
t.start();
t.stop();
t.end();

输出将是:

Started
Has quit
Done waiting
Finished

finishedwait完成后触发.为了使你的deleteLater连接生效太晚,该线程的事件循环已经死了.