[PyQt] Bug Report: QThreadPool doesn't take the ownership of QRunnable

[Phil Thompson]

On 22-03-2014 10:52 am, Hans-Peter Jansen wrote:
> Dear Phil,
>
> On Freitag, 21. März 2014 17:33:42 Phil Thompson wrote:
>> On 21-03-2014 9:43 am, Riccardo Ferrazzo wrote:
>> > Hi,
>> > In PyQt5 i'm having problems due to deleted objects inside the
>> > QThreadPool.
>> > I've created a simple example to prove the existence of the 
>> problem:
>> >
>> > from PyQt5.QtCore import *
>> > from time import sleep
>> >
>> > class Test(QRunnable):
>> >     def __init__(self):
>> >         QRunnable.__init__(self)
>> >
>> >     def run(self):
>> >         sleep(10)
>> >         print(self, "Awake!")
>> >
>> >     def __del__(self):
>> >         print(self, "Deleted")
>> >
>> > def run_thread():
>> >     t = Test()
>> >     QThreadPool.globalInstance().start(t)
>> >
>> > if __name__ == "__main__":
>> >     for i in range(10):
>> >         run_thread()
>> >
>> >     sleep(20)
>> >
>> > It prints out:
>> > (<__main__.Test object at 0x7feb8499fc30>, 'Deleted')
>> > (<__main__.Test object at 0x7feb8499fc30>, 'Deleted')
>> > (<__main__.Test object at 0x7feb8499fc30>, 'Deleted')
>> > (<__main__.Test object at 0x7feb8499fc30>, 'Deleted')
>> > (<__main__.Test object at 0x7feb8499fc30>, 'Deleted')
>> > (<__main__.Test object at 0x7feb8499fc30>, 'Deleted')
>> > (<__main__.Test object at 0x7feb8499fc30>, 'Deleted')
>> > (<__main__.Test object at 0x7feb8499fc30>, 'Deleted')
>> > (<__main__.Test object at 0x7feb8499fc30>, 'Deleted')
>> > (<__main__.Test object at 0x7feb8499fcc8>, 'Deleted')
>> > (<__main__.Test object at 0x7feb8499fc30>, 'Awake!')
>> > (<__main__.Test object at 0x7feb8499fc30>, 'Deleted')
>> > (<__main__.Test object at 0x7feb8499fcc8>, 'Awake!')
>> > (<__main__.Test object at 0x7feb8499fcc8>, 'Deleted')
>>
>> The main problem should be fixed in tonight's snapshot. You can work
>> around it by keeping an explicit reference to the global 
>> QThreadPool.
>>
>> However there still seems to be a problem. My system hangs when the
>> thread pool is exhausted - it seems unable to re-use a thread. 
>> However
>> putting a sleep() (for 4 seconds in my case) after the call to 
>> start()
>> makes everything work. Using a shorter delay allows about 7 runs 
>> before
>> hanging.
>
> Due to considerable differences in threading implementations of all
> supported
> OS of Qt, it would be nice to refer to the variant, you're testing 
> with.
> Especially behavior differences of windows and non-windows platforms 
> is
> interesting.
>
> While one can safely imply current versions of Qt5, sip and PyQt5 in
> your case
> ;), for later reference, it would be kind to mention versions of main 
> actors
> here..
>
> Cheers,
> Pete

Sure...

I do all my development on OS/X (Mavericks). The default size of the 
thread pool is 2.

Phil