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From: Gene Heskett <gheskett@wdtv.com>
To: python-list@python.org
Subject: Re: subprocess call is not waiting.
Date: Wed, 19 Sep 2012 11:57:47 -0400
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On Wednesday 19 September 2012 11:56:44 Hans Mulder did opine:

> On 19/09/12 12:26:30, andrea crotti wrote:
> > 2012/9/18 Dennis Lee Bieber <wlfraed@ix.netcom.com>:
> >>         Unless you have a really massive result set from that "ls",
> >>         that
> >> 
> >> command probably ran so fast that it is blocked waiting for someone
> >> to read the PIPE.
> > 
> > I tried also with "ls -lR /" and that definitively takes a while to
> > run, when I do this:
> > 
> > proc = subprocess.Popen(['ls', '-lR', '/'], stdout=subprocess.PIPE,
> > stderr=subprocess.PIPE)
> > 
> > nothing is running, only when I actually do
> > proc.communicate()
> > 
> > I see the process running in top..
> > Is it still an observation problem?
> 
> Yes: using "top" is an observation problem.
> 
> "Top", as the name suggests, shows only the most active processes.
> 
Which is why I run htop in a shell 100% of the time.  With htop, you can 
scroll down and see everything.

> It's quite possible that your 'ls' process is not active, because
> it's waiting for your Python process to read some data from the pipe.
> 
> Try using "ps" instead.  Look in thte man page for the correct
> options (they differ between platforms).  The default options do
> not show all processes, so they may not show the process you're
> looking for.
> 
> > Anyway I also need to know when the process is over while waiting, so
> > probably a thread is the only way..
> 
> This sounds confused.
> 
> You don't need threads.  When 'ls' finishes, you'll read end-of-file
> on the proc.stdout pipe.  You should then call proc.wait() to reap
> its exit status (if you don't, you'll leave a zombie process).
> Since the process has already finished, the proc.wait() call will
> not actually do any waiting.
> 
> 
> Hope this helps,
> 
> -- HansM


Cheers, Gene
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