throwing exceptions across thread boundaries (using QtConcurrent)

[glenn]

Thanks for your responses.
I can now see that the code i posted can indeed not work as is.
However shouldn't i be able to catch the exception when i use a QFuture with the QtConcurrent::run() and call future.result() in a slot connected to QFutureWatcher::finished() ?

I tried to do this but it does not work either..

[wysota]

No, because it has no way of knowing you are calling it from a slot connected to finished. And even if it did, it still wouldn't make sense to thow an exception there, result() is only a getter and nothing bad can happen after finished() is signalled as there are no more threads performing the job.

[magalha]

I have a similar problem with the following piece of code (Manager :: processPlugins is a valid method that receives 3 ints as parameters; the piece of code is inside a method that belongs to a Manager instance)

1. QList<QFuture<void> > workers;
2. int numWorkers = QThread::idealThreadCount();
3. for( int worker = 0; worker < numWorkers; worker++ ){
4. workers.push_back( QtConcurrent::run(
5. this,
6. &Manager :: processPlugins,
7. worker,
8. 2,
9. 3);
10. }
11. for( int worker = 0; worker < workers.size(); worker++ ) {
12. try {
13. workers[worker].waitForFinished();
14. } catch ( MyException& ex ) {
15. printf( "Exception thrown\n" );
16. }
17. }

However, when a MyException instance is thrown inside processPlugins, the catch block does not execute. Instead, the application terminates, and this warning appears:

Qt Concurrent has caught an exception thrown from a worker thread.
This is not supported, exceptions thrown in worker threads must be
caught before control returns to Qt Concurrent

Am I missing something?
Thanks for any help

Cheers,
João Magalhães