Qt：QRunnable的moveToThread问题（QObject::moveToThread: Current thread (***) is not the object‘s thread）

问题描述：

主线程new了一个QRunnable，然后加入到线程池中运行。QRunnable::run中发起一个异步调用，然后希望在线程池的QRunnable所在的运行线程获取异步调用的完成回调通知。

因此，在QRunnable::run中调用QObject::connect来连接异步调用的信号槽，使用Qt::QueuedConnection方式连接。但最终回调通知被传递到了主线程，而不是QRunnable::run所在线程。

试图在QRunnable::run的开头调用moveToThread修改QRunnable的对象归属线程，但执行结果一样，并提示 QObject::moveToThread: Current thread (***) is not the object‘s thread。

解决方法：

简单查阅了一下文档。如下：

void QObject::moveToThread(QThread *targetThread)
Changes the thread affinity for this object and its children. The object cannot be moved if it has a parent. Event processing will continue in the targetThread.
To move an object to the main thread, use QApplication::instance() to retrieve a pointer to the current application, and then use QApplication::thread() to retrieve the thread in which the application lives. For example:
myObject->moveToThread(QApplication::instance()->thread());

If targetThread is nullptr, all event processing for this object and its children stops, as they are no longer associated with any thread.
Note that all active timers for the object will be reset. The timers are first stopped in the current thread and restarted (with the same interval) in the targetThread. As a result, constantly moving an object between threads can postpone timer events indefinitely.
A QEvent::ThreadChange event is sent to this object just before the thread affinity is changed. You can handle this event to perform any special processing. Note that any new events that are posted to this object will be handled in the targetThread, provided it is not nullptr: when it is nullptr, no event processing for this object or its children can happen, as they are no longer associated with any thread.

Warning: This function is not thread-safe; the current thread must be same as the current thread affinity. In other words, this function can only “push” an object from the current thread to another thread, it cannot “pull” an object from any arbitrary thread to the current thread. There is one exception to this rule however: objects with no thread affinity can be “pulled” to the current thread.

See also thread().

加粗加蓝的部分应该就是原因所在。即，只能将当前线程的对象设置为别的线程，也就是只能“推”；不能将别的线程的对象设置到当前线程，也就是不能“拉”。

本人所遇到的情况，就是试图“拉”。由于是线程池，自然就没法“推”，因为运行之前目标线程不一定。但“拉”是无效的，所以失败，提示 QObject::moveToThread: Current thread (***) is not the object‘s thread。

于是，本人新加了一个专门接收异步回调信号的自定义类A，在QRunnable::run中new A，然后连接这个新对象，一切正常。

转载请注明来源，谢谢。

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