Using signal.alarm to terminate a thread

[Nick Craig-Wood]

Adrian Casey <adrian.casey at internode.on.net> wrote:
>  I have a multi-threaded python application which uses pexpect to connect to
>  multiple systems concurrently.  Each thread within my application is a
>  connection to a remote system.  The problem is when one of the child
>  threads runs a command which generates an unlimited amount of output.  The
>  classic example of this is the "yes" command.  If you
>  execute "pexpect.run('yes')", your cpu will sit at 100% forever.
> 
>  Here is a simple multi-threaded program using pexpect which demonstrates the
>  problem.  The command 'yes' is run in a thread.  The parent says that when
>  the alarm goes off, run the handler function.  The thread sets the alarm to
>  trigger after 5 seconds.

1) Don't ever mix threads and signals - you are heading for trouble!

2) pexpect has a timeout parameter exactly for this case

import os, pexpect, threading

def runyes():
        print "Running yes command..."
        pexpect.run('yes', timeout=5)

t = threading.Thread(target=runyes)
t.start()
t.join()

-- 
Nick Craig-Wood <nick at craig-wood.com> -- http://www.craig-wood.com/nick