Shutting down threads prematurely

[Lumbricus]

My bad cut the post to short, i will try to reexplain:

I make my worker object and create a thread, then move the object to the thread and start the thread.

the started signal of the thread is connected to the slot of the worker i want to run e.g (comets_to_use() ).

the worker contains a slot called on_shut_down_threads(). inside that i was using QThread::currentThread() to access the thread that was executing the worker. So i press a button and that emits a signal with is connected to this worker slot.

So this worker is in the worker thread:

void Worker:on_shut_down_threads()
{
QThread::currentThread()->exit();
}

void Worker:on_shut_down_threads()
{
QThread::currentThread()->exit();
}

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Since i want to close down the calculations in the slot comets_to_use() before it has finished I'm trying to find a way shut down that thread/or stop executing that worker slot.

yes emitting the signal ->quit() was dumb.

i still dont see why my thread does not close if i run

active_threads[i]->terminate();

active_threads[i]->terminate();

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or:

active_threads[i]->exit();

active_threads[i]->exit();

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from the main thread thow?

[anda_skoa]

the worker contains a slot called on_shut_down_threads(). inside that i was using QThread::currentThread() to access the thread that was executing the worker.

QThread::currentThread() returns the current thread.
If that is in the slot called by the main thread, then the main thread is the current thread.

So i press a button and that emits a signal with is connected to this worker slot.

So it depends on how the connection() was created.
In an AutoConnection the receiver object's thread executes the slot, in a QueuedConnection the signal emitting thread executes the slot.

So if you have a QueuedConnection as you claim, then accessing the current thread will never access the worker thread as it is not the current thread.

i still dont see why my thread does not close if i run

active_threads[i]->terminate();

active_threads[i]->terminate();

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or:

active_threads[i]->exit();

active_threads[i]->exit();

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QThread::exit() is basically the same as QThread::quit(), both make the thread's event loop end.

Lets go back to your need to that kind of threading approach.
Aside from the slot that is run on start, what other slots does the worker have and how does the main thread trigger them?

Cheers,
_

[Lumbricus]

okai back to basics:

for (int id=1;id<=guidata.numbers_of_workerthreads;id++)
    {
 
    QThread *thread = new QThread;
 
    Worker *worker = new Worker(&guidata,ui,id,&m_c,&mutex_file,&mutex_count);
 
    worker->moveToThread(thread);
 
    //connect events from worker<-> threads
    connect(worker, SIGNAL(error(QString)), this, SLOT(errorString(QString)));
    connect(thread, SIGNAL(started()), worker, SLOT(comets_to_use())); // when i start the thread it automaticly runs my slot that i specify
    connect(this, SIGNAL(shut_down_threads()), worker ,SLOT(on_shut_down_threads())); 
    connect(worker, SIGNAL(finished()), thread, SLOT(quit()));
    connect(worker, SIGNAL(finished()), worker, SLOT(deleteLater()));
    connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()));
 
    thread->start();
    }
}

for (int id=1;id<=guidata.numbers_of_workerthreads;id++)
    {
 
    QThread *thread = new QThread;
 
    Worker *worker = new Worker(&guidata,ui,id,&m_c,&mutex_file,&mutex_count);
 
    worker->moveToThread(thread);
 
    //connect events from worker<-> threads
    connect(worker, SIGNAL(error(QString)), this, SLOT(errorString(QString)));
    connect(thread, SIGNAL(started()), worker, SLOT(comets_to_use())); // when i start the thread it automaticly runs my slot that i specify
    connect(this, SIGNAL(shut_down_threads()), worker ,SLOT(on_shut_down_threads())); 
    connect(worker, SIGNAL(finished()), thread, SLOT(quit()));
    connect(worker, SIGNAL(finished()), worker, SLOT(deleteLater()));
    connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()));
 
    thread->start();
    }
}

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this is how i start a specific method in the worker other methods like my calc_stream_allcomets() ... would get exchanged with comets_to_use(); Depending on what button is clicked on the gui the worker slot that is executed on start is varied.

As i said the calculations can be up to 1-2 days and sometimes i want to shut down the threads earlier e.g when you notice you made an input mistake of somekind.

[anda_skoa]

Ok, so depending on what you want to do you have a different slot of the worker connected to the thread's started() signal, but in all cases one worker object is only ever used for one operation and either cancelled or fully executed and then discarded.

Ok, then comets_to_use() and any of the other operations that need to be interruptible need check whether they need to stop.
And the slot connected to shut_down_threads() needs to be connected with a DirectConnection and needs to change whatever the worker does to check for stopping.

One option would be to check the worker's thread isInterruptionRequested() and use the worker's thread requestInterrruption() to switch to stopping.
The worker would then also make the thread quit its event loop right before it exits the processing function.

Cheers,
_

[Lumbricus]

That sounds like a good approach to me. I'm still unclear how i would stop the worker from doing what it is doing to check if an interruption is wanted.

What do I put in the worker slot that is connected? How would I change the worker from "working on my stuff". This is the Worker slot that is connected by direct connection to the main thread.

void Worker::on_shut_down_threads()
{
    if("workerthread_pointer?"->isInterruptionRequested())
    {
        ??
    } 
 
}

void Worker::on_shut_down_threads()
{
    if("workerthread_pointer?"->isInterruptionRequested())
    {
        ??
    } 

}

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Am i Understanding u right? I think a little pseudo code or code would help me understand

[anda_skoa]

No, in that slot you request the interruption.

void Worker::on_shut_down_threads()
{
    thread()->requestedInterruption();
}

void Worker::on_shut_down_threads()
{
    thread()->requestedInterruption();
}

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The method that does the long calculation needs regularily to check for interruption.

Cheers,
_

[Lumbricus]

Okai anda,

i think i've nearly understood, thx for your patience!

In my worker slot i now have a check that is run through every 2sek. It checks if there is an interruption request from the main thread. The interrupt request is passed through with a direct connection. This is working at the moment. so in this part of the code how do i shut down the thread?


this is in the executing worker slot (comets_to_use()) in the worker thread:

//...worker doing stuff...
 
//comes past here every 2 sek
 
if (interruptRequested)
{
    how do i shut down the thread from here?
}

//...worker doing stuff...

//comes past here every 2 sek

if (interruptRequested)
{
    how do i shut down the thread from here?
}

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the only way i got it to work was to put this request at the beginning of all my nested loops and break; out of them so i quickly reach the end of the slot. then the thread processes my finished() signal and destructs normaly. is there a nicer way to do this?

[anda_skoa]

You can nest the calls

void Worker::comets_to_use()
{
    comets_to_use_internal();
    thread()->quit();
}

void Worker::comets_to_use()
{
    comets_to_use_internal();
    thread()->quit();
}

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That way you can just return from comets_in_use_internal() whenever you want to end.

Cheers,
_