QThread hungs up when calling isRunning on it

Question

I have a QThread that fetches data from the web. Sometimes the user asks for something else, and the data needs to be fetched changes as well.

In my current configuration, I call terminate() upon the thread, change the input data, and call start() on the thread again. Now, that works fine, but sometimes I get the main eventloop stuck when calling isRunning() or isFinished() upon a terminated thread. It gets stuck forever, and does not recover until I kill the process.

Why would isRunning() or isFinished() hung in the first place? They don't suppose to block.
Is this workflow acceptable? If not, how can I stop a thread's process when I don't need it no more (or how can I abandon it)?

score 1 · Answer 1 · answered Nov 03 '12 at 19:51

1

Don't use terminate(), read the warning in the documentation.

Whil it is possible to restart a QThread, restarting threads usually is not a good idea, there should be a better solution to do what you're trying to do.

answered Nov 03 '12 at 19:51

mata

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My thread doesn't hold any mutexes. It fetches data from the web and sends it to the main thread through a signal. Killing it anytime is fine, and it doesn't need to cleanup a thing. Plus, killing off threads doesn't suppose to break `isRunning()`'s behavior. – iTayb Nov 04 '12 at 00:00
What about the mutexes held by the QThread itself? I bet [this](http://qt.gitorious.org/qt/qt/blobs/4.8/src/corelib/thread/qthread.cpp#line465) is where `isRunning` is hanging, but it's hard to say, I can't reproduce it. – mata Nov 04 '12 at 01:13

score 0 · Accepted Answer · answered Nov 08 '12 at 22:52

It seems that in some cases, the thread becomes unusable after termination, and isRunning() and isFinished() may hang the calling thread, even if called only after the TERMINATED signal.

My workaround was to terminate a thread, forget about it and start a new one.

QThread hungs up when calling isRunning on it

2 Answers2