PyQt and async I/O

djw donald.welch.nospam at hp.com
Tue Jul 1 23:01:43 CEST 2003


Greetings-

I was looking at the ASPN recipe for async I/O and Tkinter:

http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/82965

I am interested in using the recipe that is provided in the comments section
for PyQt courtesy of Laura Creighton. 

I have a question though....

In the code, it says:

        "One important thing to remember is that the thread has to yield
        control."

That appears in this code (the thread that will contain the async I/O):

def workerThread1(self):
        """
        This is where we handle the asynchronous I/O. For example, it may be
        a 'select()'.
        One important thing to remember is that the thread has to yield
        control.
        """
        while self.running:
            # To simulate asynchronous I/O, we create a random number at
            # random intervals. Replace the following 2 lines with the real
            # thing.
            time.sleep(rand.random() * 0.3)
            msg = rand.random()
            self.queue.put(msg)


If you were to use asyncore for this async I/O, there is no yielding that I
can see. Select() doesn't yield, and there is no time.sleep() in the
asyncore.loop() code. Even if I were to add a time.sleep() to the loop,
wouldn't the fact that select() blocks for some timeout value (default=30.0
sec) imply that it would only yield after the select() timed out each time
through the loop? That would seem to make for a pretty unresponsive UI. 

Hopefully somebody can clue me into understanding this.

Thanks,

Don





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