[Tutor] Multi-Threading and KeyboardInterrupt
mk.fraggod at gmail.com
Sat Jun 13 07:25:45 CEST 2009
On Thu, 11 Jun 2009 22:35:15 -0700
Dennis Lee Bieber <wlfraed at ix.netcom.com> wrote:
> On Thu, 11 Jun 2009 08:44:24 -0500, "Strax-Haber, Matthew (LARC-D320)"
> <matthew.strax-haber at nasa.gov> declaimed the following in
> > I sent this to the Tutor mailing list and did not receive a response.
> > Perhaps one of you might be able to offer some sagely wisdom or pointed
> > remarks?
> > Please reply off-list and thanks in advance. Code examples are below in
> > plain text.
> Sorry -- you post to a public forum, expect to get the response on a
> public forum...
> > > My program runs interactively by allowing the user to directly
> > > interact with the python prompt. This program has a runAll() method
> > > that runs a series of subprocesses with a cap on how many instances
> > > are running at a time. My intent is to allow the user to use Ctrl-C to
> > > break these subprocesses. Note that while not reflected in the demo
> Are they subprocesses or threads? Your sample code seems to be using
> When using threads, there is no assurance that any thread other than
> the main program will receive a keyboard interrupt.
In fact, no thread other than the main will get interrupt.
> > def runAll():
> > workers = [ Thread(target = runSingle, args = [i])
> > for i in xrange(MAX_SUBPROCS + 1) ]
> > try:
> > for w in workers:
> > w.start()
> > except KeyboardInterrupt:
> > ## I want this to be shown on a KeyboardInterrupt
> > print '********* stopped midway ********'
> You are unlikely to see that... After you start the defined worker
> /threads/ (which doesn't take very long -- all threads will be started,
> but some may immediately block on the semaphore) this block will exit
> and you will be at...
> > for w in workers:
> > w.join()
> ... a .join() call, which is the most likely position at which the
> keyboard interrupt will be processed, killing the main program thread
> and probably generating some errors as dangling active threads are
> forceably killed.
There was quite interesting explaination of what happens when you send
^C with threads, posted on concurrency-sig list recently:
Can be quite shocking, but my experience w/ threads only confirms that.
Mike Kazantsev // fraggod.net
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