[SOLVED] Wait for timeout or some signal

[maxim.prishchepa]

tnx a lot!

[rich]

Please don't use processEvents() like this, or your CPU usage will be terrible. Instead use QEventLoop.

[joonhwan]

@rich,
Can hear more details of using processEvents() and QEventLoop story here?

[andre]

Calling processEvents() in a loop like proposed will keep your CPU 100% bussy, because you just keep polling the event queue. Using an eventloop is a smarter solution that doesn't waste CPU cycles like that, so it will not spike your CPU. It is also the solution implemented by the libQxt in QxtSignalWaiter.

[joonhwan]

@Andre,
Thanks, feel like got good things to know and even another useful-looking library!

[RomaHagen]

QxtSignalWaiter is implemented with a help of processEvents, not eventLoop. See "here":http://dev.libqxt.org/libqxt/src/21ea5919eabb2a404eafdffcdb8383472ca66bdd/src/core/qxtsignalwaiter.cpp?at=master#cl-143.

[andre]

[quote author="RomaHagen" date="1357227120"]QxtSignalWaiter is implemented with a help of processEvents, not eventLoop. See "here":http://dev.libqxt.org/libqxt/src/21ea5919eabb2a404eafdffcdb8383472ca66bdd/src/core/qxtsignalwaiter.cpp?at=master#cl-143. [/quote]

Hmmm... You're right. Surprising. Thanks for the correction.

Does anyone know why Qxt choose this implementation instead?

[RomaHagen]

See "this":http://dev.libqxt.org/libqxt/src/21ea5919eabb2a404eafdffcdb8383472ca66bdd/src/core/qxtsignalwaiter.cpp?at=master#cl-143 and read the doc about WaitForMoreEvents "here":http://qt-project.org/doc/qt-4.8/qeventloop.html#ProcessEventsFlag-enum.

[andre]

Yes, I know where to find the sources and I know the docs, but that was not my question. I sometimes use this idea:
@
QEventLoop loop;
connect(myObject, SIGNAL(theSignalToWaitFor()), &loop, SLOT(quit()));
connect(timeoutTimer, SIGNAL(timeout()), &loop, SLOT(quit()));
loop.exec(); //blocks untill either theSignalToWaitFor or timeout was fired
@

[Mar4eli]

[quote author="Andre" date="1357286986"]Yes, I know where to find the sources and I know the docs, but that was not my question. I sometimes use this idea:
@
QEventLoop loop;
connect(myObject, SIGNAL(theSignalToWaitFor()), &loop, SLOT(quit()));
connect(timeoutTimer, SIGNAL(timeout()), &loop, SLOT(quit()));
loop.exec(); //blocks untill either theSignalToWaitFor or timeout was fired
@

[/quote]

thank you. it's very useful.