PyQt: user interface freezed when using concurrent.futures.ThreadPoolExecutor

[Michael Torrie]

On 12/10/2014 09:52 PM, iMath wrote:
> I think the user interface shouldn't be freezed when using
> concurrent.futures.ThreadPoolExecutor here,as it executes
> asynchronously , but it doesn't meet my expectations,anyone can
> explain why ? any other solutions here to not let user interface
> freezed?
> 
> code is here 
> http://stackoverflow.com/questions/27393533/user-interface-freezed-when-using-concurrent-futures-threadpoolexecutor

In most any GUI framework, regardless of your use of threads, your
callbacks must return control to the main loop immediately (whether an
on-click or an on-timer event), or the GUI *will* freeze.

You are spawning threads to download the urls, then sitting there
waiting for them to finish in the callback.  Of course the GUI will
freeze; your callback is blocking it.  What you should be doing is
spawning the threads to do the download, then have the threads (using a
proper QThread mechanism or some other semaphore mechanism) raise a
signal to indicate they are done, which you will then catch in the main
loop as a normal callback.  And really when it comes to I/O and GUIs,
asynchronous calls are always better than threads.  Not sure what Qt has
in the way of asynchronous i/o calls, and I'm not familiar enough with
the various async i/o frameworks in Python to speak to that, though I
did use Python-Twisted once... very powerful once you get your head
wrapped around it.

Look through the list archives because in the last 3 or 4 weeks I and
another Python user talked proper thread use with PyQt or PySide, with
code examples.