QThreadpool/QRunnable blocking
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Hello everyone,
Still a Qt rookie. I'm trying to implement the example of the HelloWorldTask on the QThreadpool page within my existing application. The HelloWorldTask is called within a slot, executes one time, and then blocks execution thereafter. My code:
class HelloWorldTask : public QRunnable { void run() override; }; void HelloWorldTask::run() { qDebug() << "Hello world from thread" << QThread::currentThread(); } void slotTask() { ...do stuff... HelloWorldTask *hello = new HelloWorldTask(); pool->tryStart(hello); ...resume doing stuff... }I want the HelloWorldTask to execute every time the slot triggers. My understanding was that this would hand off the task as a worker thread and the remaining code in my slot would continue to execute, but it seems to block all execution. Do I need to call a wait somewhere? Do I need to call releaseThread? Kinda lost.
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Hi,
What do you mean by block all execution ?
How did you determine that ?
Which version of Qt ?
On which platform ? -
What do you mean by block all execution ?Whereas my program normally continues running and the slotTask will be triggered almost constantly, the program hangs after the 'hello from thread x' statement.
How did you determine that ?Output to the console window stops. Execution (and console output) would normally continue until I terminate the program.
Which version of Qt ?5.9.3 -- not chosen by me, so I'm stuck with it.
On which platform ?Windows 10
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Does it block directly on the first tryStart call ?
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How long does it block ?
You're runnable being pretty short and quick to do, you might just see it done sooner that what you expect.
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Hello everyone,
Still a Qt rookie. I'm trying to implement the example of the HelloWorldTask on the QThreadpool page within my existing application. The HelloWorldTask is called within a slot, executes one time, and then blocks execution thereafter. My code:
class HelloWorldTask : public QRunnable { void run() override; }; void HelloWorldTask::run() { qDebug() << "Hello world from thread" << QThread::currentThread(); } void slotTask() { ...do stuff... HelloWorldTask *hello = new HelloWorldTask(); pool->tryStart(hello); ...resume doing stuff... }I want the HelloWorldTask to execute every time the slot triggers. My understanding was that this would hand off the task as a worker thread and the remaining code in my slot would continue to execute, but it seems to block all execution. Do I need to call a wait somewhere? Do I need to call releaseThread? Kinda lost.
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How long does it block ?
You're runnable being pretty short and quick to do, you might just see it done sooner that what you expect.
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What do you mean by stop ?
Does your application hang or crashes ? -
void HelloWorldTask::run() { qDebug() << "Hello world from thread" << QThread::currentThread(); }@John-Howe Does your implementation contains these statements only in run method? or any while loop ?
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Made a couple of tweaks and turned on some print statements in a different part of the app (a different slot triggered by QTimer).
It almost looks like slotTask just stops printing to the console and log file.
@John-Howe the
qDebugstream is serialized internally, which is what @nagesh is alluding to, I imagine. That notwithstanding, you should just interrupt the debugger when the program hangs, and extract a complete stack trace. Upload it somewhere/post it here, so we can take a look.
