A potential issue in AppLogController

[Evgeniy Stepanov]

Hello!
I was browsing your code and I noticed one potential issue that I’ve faced once myself. I used similar implementation to display debug output in QML ListView item and got very rare spontaneous crashes without any visible reasons, the log was useless and even misleading in this case.

The problem was in a message handler, similar to your AppLogController::append. It’s not thread safe and since this message handler is executed in the thread that generates the message, you might get race condition on your model if you have qDebug or friends in different threads.

[Michael Zanetti]

Oh, interesting... Thanks for the hint! I do the same in nymea core. Haven't noticed any crashes which could be related to this, but it sure does sound like your reasoning makes sense. I'll have to look at this.

[Evgeniy Stepanov]

It's not easy to catch in the wild, but quite easy to reproduce with something like this:
QThreadPool p;
p.setMaxThreadCount(10);
QtConcurrent::run(&p,&{while(true){QThread::msleep(1); qDebug()<<"";}});
QtConcurrent::run(&p,&{while(true){QThread::msleep(2); qDebug()<<"";}});
QtConcurrent::run(&p,&{while(true){QThread::msleep(3); qDebug()<<"";}});

[Michael Zanetti]

@stepanove thanks again for reporting this. I could reproduce it with your snippet. Great catch!