Qt跨线程的槽函数执行

定义两个类：Receiver接收信号，等待2秒后执行。Sender发送信号触发Receiver槽函数的执行

class Receiver : public QObject {Q_OBJECT
public slots:void exec() {QThread::sleep(1);qDebug() << QThread::currentThreadId() << "receiver exec";}
};class Sender : public QObject {Q_OBJECT
public:void exec() {emit sig();qDebug() << QThread::currentThreadId() << "sender exec";}
signals:void sig();
};

1. moveToThread()，但是直接调用

将sender对象放入线程，但是显示调用sender对象的exec()方法，此时moveToThread不起作用，receiver和sender都在主线程中执行，sender发送信号时，会等待receiver的槽函数执行完毕才执行后续的输出

int main(int argc, char *argv[])
{QCoreApplication a(argc, argv);Receiver* r = new Receiver();Sender* s = new Sender();QObject::connect(s, SIGNAL(sig()), r, SLOT(exec()));QThread* thread = new QThread();s->moveToThread(thread);thread->start();s->exec();QThread::sleep(1000);return a.exec();
}

2. 槽函数在子线程中执行

将receiver放到单独的线程中，sender在主线程中发信号触发receiver的槽函数。此时默认槽函数连接方式Qt::AutoConnection等同于Qt::QueuedConnection，槽函数在子线程中执行，sender发送信号后立刻执行输出语句

额外的：

子线程必须通过start()开启，否则receiver
如果指定槽函数的连接方式为Qt::DirectConnection，槽函数也会在主线程中执行

int main() {Receiver* r = new Receiver();Sender* s = new Sender();QObject::connect(s, SIGNAL(sig()), r, SLOT(exec()));QThread* thread = new QThread();r->moveToThread(thread);thread->start();s->exec();QThread::sleep(1000);
}

3. 信号循环发送，但槽函数执行速度慢

将Sender类的exec()函数改为循环执行5次，发送5次信号会直接执行完成。Receiver中的槽函数正常执行5次，执行过程不会被新来的信号打断

class Sender : public QObject {Q_OBJECT
public:void exec() {for (int i = 0; i < 5; i++) {emit sig();qDebug() << QThread::currentThreadId() << "sender exec";}}
signals:void sig();
};

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4. 一次触发两个槽函数

Sender中一次发送两个信号，分别触发Receiver中的两个槽函数，一个延迟1s执行一个立即执行。槽函数按照发送信号的顺序执行。

class Sender : public QObject {Q_OBJECT
public:void exec() {for (int i = 0; i < 5; i++) {emit sig();emit sig2();qDebug() << QThread::currentThreadId() << "sender exec";}}
signals:void sig();void sig2();
};class Receiver : public QObject {Q_OBJECT
public slots:void exec() {QThread::sleep(1);qDebug() << QDateTime::currentDateTime() << QThread::currentThreadId() << "receiver exec";}void exec2() {qDebug() << QDateTime::currentDateTime() << QThread::currentThreadId() << "receiver exec2";}
};