[Interest] QEventLoop -- not sure I am correctly using this

Thu Dec 5 06:12:55 CET 2013

>
> //now some condition occurs, I want the worker on the inside to start
> doing its thing
> manager->startWorker();
>

I assume your "worker object" (which runs inside another thread) will have
public slots to start/stop its work.

If so, you can either connect a signal from the main thread to these slots
or use the "invokeMethod" API to call these slots on some event. Since the
worker object resides in a different thread, your slot invocation will be
"queued" and will get run in the worker thread's context.

HTH,
-mandeep

> …
> …
> …
> //now some other condition occurs, I want the worker on the inside to stop
> doing its thing
> manager->stopWorker();
>
>
> Alternatively, through the signal/slot mechanism.  Regardless, will the
> above pull it out of its thread?
>
> Thanks,
>
> -Jason
>
> *- - - - - - - - - - - - - - - - - - - - - - -*
> *Jason R. **Kretzer*
>
> *Application Developer*
> *Google # 606-887-9011 <606-887-9011>*
> *Cell # 606-792-0079 <606-792-0079>*
> *Jason at gocodigo.com <Jason at gocodigo.com>*
>
> *“quidquid latine dictum sit altum videtur”*
>
>
>
> On Dec 4, 2013, at 12:46 AM, Mandeep Sandhu <mandeepsandhu.chd at gmail.com>
> wrote:
>
>
> On Tue, Dec 3, 2013 at 10:39 PM, Jason Kretzer <Jason at gocodigo.com> wrote:
>
>> Ah, I see!  Now I understand what you mean.
>>
>> I rewrote my “player” object to use a Qtimer that fires every 1 second
>> and is started/stopped according to signals.  However, it still has the
>> same problem where the timer won’t fire sometimes for extended periods.  I
>> guess that means something in the overall eventloop is blocking it.  So, I
>> believe I will try to implement it in the worker kind of format you have
>> below where I can put the timer in a thread.
>>
>
> Also, as Thiago already suggested, while you're debugging, print out the
> thread ID from the worker thread and main thread objects just so that you
> know that they're running in different threads.
>
> -mandeep
>
>
>
>>
>> I appreciate the help!
>>
>> -Jason
>>
>>  *- - - - - - - - - - - - - - - - - - - - - - -*
>> *Jason R. **Kretzer*
>>
>> *Application Developer*
>> *Google # 606-887-9011 <606-887-9011>*
>> *Cell # 606-792-0079 <606-792-0079>*
>> *Jason at gocodigo.com <Jason at gocodigo.com>*
>>
>> *“quidquid latine dictum sit altum videtur”*
>>
>>
>> <image001.png>
>>
>> On Dec 2, 2013, at 11:58 PM, Mandeep Sandhu <mandeepsandhu.chd at gmail.com>
>> wrote:
>>
>> Hi Jason,
>>
>>
>> As Andre pointed out, have an 'outer' class manage the worker object
>> and thread for you instead of doing it from within your worker.
>>
>> Eg:
>>
>> SomeManagerClass::SomeManagerClass(QObject *parent) : QObject(parent)
>> {
>>    worker = new MyWorker(); // parentless
>>    workerThread = new QThread(); // parentless
>>
>>    // Move worker object to new thread
>>    worker->moveToThread(workerThread);
>>
>>    connect(worker, SIGNAL(workFinished()), this, SLOT(onWorkFinished()));
>>
>>    workerThread->start();
>> }
>> ...
>> ...
>> SomeManagerClass::~SomeManagerClass()
>> {
>>    workerThread->quit();
>>    workerThread->wait();
>> }
>>
>> As for you event loop, I don't see any obvious issues.
>>
>> I guess the reason you decided to wait for 1 second using an ev loop,
>> rather than have a slot handle the timeout was to make the code look
>> simple (synchronous)?
>>
>> What platform are you running this on?
>>
>> -mandeep
>>
>>
>> On Tue, Dec 3, 2013 at 1:59 AM,  <andre at familiesomers.nl> wrote:
>>
>> Hi,
>>
>> It looks to me, that you're indeed doing it wrong. It seems you're
>> trying to let your backgroundtaskmanager both manage a thread and be
>> _in_ that thread. That is not the way to go. I'd separate the two
>> issues. If you want the backgroundTaskManager to run in it's own thread,
>> then either just make it a "front" for a backend implementation that you
>> move to a thread managed by backgroundTaskManager, or just let let the
>> whole backgroundTaskManager be unconcerned with what thread it runs in,
>> and have whoever creates/owns/manages it be responsible for moving it to
>> a separate thread if that is desirable.
>>
>> Then about your use of QEventLoop: no, I'd not use it this way.
>> QEventLoop is not meant as an escape to 'pause' execution of your
>> method. If you want to wait for about a minute, why not use a QTimer
>> directly? I don't see a need for QEventLoop here at all.
>>
>> As to why your setup doesn't work and your eventloop seems blocked
>> during your background task: I guess you gave your BackgroundTaskManager
>> a parent object? That won't work. A whole parent/child tree must live in
>> the same thread. So, I guess your BackgroundTaskManager did not actually
>> get moved to the thread at all.
>>
>> André
>>
>>
>> Jason Kretzer schreef op 02.12.2013 20:27:
>>
>> Maybe that last bit would be a bit more clear.
>>
>> The first qDebug statement writes out — I have it set to give the
>> time when it is written as well — but the qDebug does not write
>> until after the heavy task is completed in backgroundtaskmanager. Any
>> other time, this performs as expected, ticking along every second.
>>
>> -Jason
>>
>> _- - - - - - - - - - - - - - - - - - - - - - -_
>> _JASON R. __KRETZER_
>> _ _
>> _APPLICATION DEVELOPER_
>> _Google # 606-887-9011_
>> _Cell # 606-792-0079_
>> _Jason at gocodigo.com_
>> _ _
>> _“QUIDQUID LATINE DICTUM SIT ALTUM VIDETUR”_
>> _ _
>>
>> On Dec 2, 2013, at 2:14 PM, Jason Kretzer <Jason at gocodigo.com> wrote:
>>
>> Good Day,
>>
>> I have in my application, two classes. When the application starts
>> up, one of the classes -backgroundtaskmanager - gets instantiated.
>> In the constructor, a QTimer is started to timeout every 5 minutes
>> and call runTasks. The instantiation is then moved to a separate
>> thread so that it can run without impacting the rest of the
>> application.
>>
>> Here are the contents of the constructor.
>>
>> QTimer* timer = new QTimer(this);
>> connect(timer, SIGNAL(timeout()), this, SLOT(runTasks()));
>> timer->start(300000); //fiveminutes
>> thread = new QThread();
>> this->moveToThread(thread);
>> thread->start();
>>
>> The second class -player- is instantiated in the main thread. Once
>> it is instantiated, it begins doing other tasks. Basically, a method
>> is called with the following code. This code is designed to make the
>> while loop delay for one second before executing the rest of the
>> loop (one second-ish, I know it is not perfect but it has good
>> enough resolution for what I need).
>>
>> while(!taskQueue.isEmpty()) {
>> qDebug() << “BEFORE QEVENTLOOP”;
>> QEventLoop wait1Sec;
>> QTimer::singleShot(1000, &wait1Sec,SLOT(quit()));
>> wait1Sec.exec();
>> aDebug() << “AFTER QEVENTLOOP”;
>>
>> QList<Task*> instances;
>> for(int t=seconds; t>previousTime; t—) {
>> QList<Task*> vals = taskQueue.values(t);
>> while(!vals.isEmpty()) {
>> instances.insert(0, vals.takeLast());
>> }
>> taskQueue.remove(t);
>> }
>> previousTime = seconds;
>> miliSeconds = QDateTime::currentMSecsSinceEpoch() -
>> today.toMSecsSinceEpoch();
>> seconds = miliSeconds/1000;
>> }
>>
>> NOTE: the two sets of tasks these do are not related.
>>
>> So, anyway, every 5 minutes the tasks in backgroundtaskmanager are
>> run. Some of these tasks can take up to a minute. When the
>> backgroundtaskmanager class runs a task that does take this long
>> (remember it is in a separate thread), the player class code above
>> gets hung in what appears to be the inside of the QEventLoop. The
>> qDebug statements don’t write out until the tasks in the
>> backgroundtaskmanager are finished. Then it rushes through to catch
>> up.
>>
>> My question is, am I correctly doing this at all? Is this the proper
>> use of a QEventLoop?
>>
>> Thanks!
>>
>> -Jason
>>
>> _- - - - - - - - - - - - - - - - - - - - - - -_
>> _JASON R. __KRETZER_
>> _ _
>> _APPLICATION DEVELOPER_
>> _Google # 606-887-9011_
>> _Cell # 606-792-0079_
>> _Jason at gocodigo.com_
>> _ _
>> _“QUIDQUID LATINE DICTUM SIT ALTUM VIDETUR”_
>> _ _
>> <image001.png>
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