QMessageBox.exec() does not block Producer-Consumer signal loop

[airproject]

Hi!,
I have a singlethreaded application which performs some longer task. The task is devided in to small portions and accomplished by Producer-Consumer, Qt::QueuedConnection, signal-slot loop. Everthing works well, gui is responsive.
I have a 'Stop' button in the gui. In its 'onClick' event handler i am displaying a confirmation message with use of QMessageBox::exec() function.

Unfortunately i am facing the following problem:
When the confirmation message is displayed, sometimes the Producer-Consumer loop is blocked and sometimes it proceeds unaffected.
I would like the modal confirmation box to block the execution of the Producer-Consumer loop.

I have read that exec() runs its own event loop and this would explain why Producer-Consumer loop proceeds. However, i am confused with the fact that sometimes it is blocked. And still.. i would like to block this loop somehow.

Any ideas?
best regards.

[amleto]

exec() makes another event loop - but you can think of this as another version of the gui event loop.

I dont think it will be interfering with the running of other threads, and I think it should not be halting the execution of slots in the gui thread.

If you want to be able to block your producer/consumer, I suggest looking at something like this:

void
myclass::slot_block()
{
  QEventLoop eventLoop;
  connect(this, SIGNAL(continue()), &eventLoop, SLOT(quit()));
  eventLoop.exec(); // will process signals/slots, but myclass
  // will not otherwise execute any more code until the loop is exited
}
 
void
myclass::slot_continue()
{
  emit continue();
}

void
myclass::slot_block()
{
  QEventLoop eventLoop;
  connect(this, SIGNAL(continue()), &eventLoop, SLOT(quit()));
  eventLoop.exec(); // will process signals/slots, but myclass
  // will not otherwise execute any more code until the loop is exited
}

void
myclass::slot_continue()
{
  emit continue();
}

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ie you need to implement two slots and a signal.

[airproject]

Thank you for the reply.
If i understand you well:
- QMessageBox::exec() - executes an event loop which processes the GUI thread signals (processes Producer-Consumer, filters out only widget signals?)
- creating new QEventLoop and running it will be processing utterly new event loop separated form GUI thred with Producer-Consumer signals. This loop will engage application processing untill i quit() it.

I guess Displaying QMessageBox should be accomplished with some other method (open(), show()) than exec().

I will do some trials.. and still wonder why sometimes the GUI thread event loop is blocked by exec() and sometimes no:/

Best regards.