[Interest] Difficulty running Timer from QThread

[Israel Brewster]

Thank you for the pointer to use QThread::currentThread for debugging! The problem was a bit more obscure than I was thinking, but that tip led me to the solution: the function that *called* the function which tried to start the timer was a VLC callback. Apparently, that callback was running in a different thread, so when it called my function *directly*, my function was also running in a different thread. By having the callback instead emit a signal which I connected to my function, my function ran in the correct thread, and I was able to start the timer properly (hopefully that all makes sense).

Thanks again!
---
Israel Brewster
Software Engineer
Alaska Volcano Observatory 
Geophysical Institute - UAF 
2156 Koyukuk Drive 
Fairbanks AK 99775-7320
Work: 907-474-5172
cell:  907-328-9145

> On Jul 18, 2021, at 8:48 PM, Nuno Santos <nuno.santos at imaginando.pt> wrote:
> 
> Israel,
> 
> Maybe the problem is that fact that you call worker initVLC(videoWin) from the main thread.
> 
> Maybe you could connect a signal to the thread started signal to call initVLC.
> 
> Try to debug QThread::currentThread() when initVLC is called and when worker is created to see if what I say makes sense.
> 
> Best,
> 
> Nuno
> 
>> On 19 Jul 2021, at 04:29, Israel Brewster <ijbrewster at alaska.edu <mailto:ijbrewster at alaska.edu>> wrote:
>> 
>> Yes, this is a FAQ, but I can’t seem to figure out what I am doing wrong. I am using the worker pattern of QThread, (as opposed to subclassing), running Qt 5.15.2. In my controller’s constructor, I have the following code to initialize a worker:
>> 
>> worker=new VLCWorker();
>> worker->moveToThread(&vlcWorkerThread);
>> worker->initVLC(videoWin);
>> vlcWorkerThread.start();
>> 
>> The initVLC function, among other things, creates a timer and connects it to a slot in the worker:
>> 
>> rtspStartTimer=new QTimer;
>> rtspStartTimer->setSingleShot(true);
>> connect(rtspStartTimer, &QTimer::timeout,
>> 	this, &VLCWorker::rtspStarting);
>> 
>> 
>> Later, at some point during program execution, I try to start this timer from a function in the worker (which itself was triggered by a signal from the main thread):
>> 
>> qDebug()<<"*****Trying to start timer which lives in thread"<<(long)rtspStartTimer->thread()<<" from thread "<<(long)this->thread();
>> rtspStartTimer->start(250);
>> qDebug()<<"*****Timer attempt complete";
>> 
>> Unfortunately, this doesn’t work, giving me the following output:
>> 
>> Debug: 2021-07-18T19:26:12.009 - *****Trying to start timer which lives in thread 140235980165688  from thread  140235980165688 (../DoorBellCamC/vlccontroller.cpp:121, void VLCWorker::rtspStarting())
>> Warning: 2021-07-18T19:26:12.009 - QObject::startTimer: Timers cannot be started from another thread (:0, )
>> Debug: 2021-07-18T19:26:12.009 - *****Timer attempt complete (../DoorBellCamC/vlccontroller.cpp:123, void VLCWorker::rtspStarting())
>> 
>> So even though the output of the debug confirms that the timer lives in the same thread I am trying to call start from, I still get the error about “timers cannot be started from another thread”. What am I doing wrong?
>> ---
>> Israel Brewster
>> Software Engineer
>> Alaska Volcano Observatory 
>> Geophysical Institute - UAF 
>> 2156 Koyukuk Drive 
>> Fairbanks AK 99775-7320
>> Work: 907-474-5172
>> cell:  907-328-9145
>> 
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