Python ignores SIGINT in multithreaded programs - how to fix that?

Question

I have Python 2.6 on MacOS X and a multithread operation. Following test code works fine and shuts down app on Ctrl-C:

import threading, time, os, sys, signal
def SigIntHandler( signum, frame ) :
  sys.exit( 0 )
signal.signal( signal.SIGINT, SigIntHandler )
class WorkThread( threading.Thread ) :
  def run( self ) :
    while True :
      time.sleep( 1 )
thread = WorkThread()
thread.start()
time.sleep( 1000 )

But if i change only one string, adding some real work to worker thread, the app will never terminate on Ctrl-C:

import threading, time, os, sys, signal
def SigIntHandler( signum, frame ) :
  sys.exit( 0 )
signal.signal( signal.SIGINT, SigIntHandler )
class WorkThread( threading.Thread ) :
  def run( self ) :
    while True :
      os.system( "svn up" ) # This is really slow and can fail.
      time.sleep( 1 )
thread = WorkThread()
thread.start()
time.sleep( 1000 )

Is it possible to fix it, or python is not intended to be used with threading?

Answer 1

A couple of things which may be causing your problem:

1. The Ctrl-C is perhaps being caught by svn, which is ignoring it.
2. You are creating a thread which is a non-daemon thread, then just exiting the process. This will cause the process to wait until the thread exits - which it never will. You need to either make the thread a daemon or give it a way to terminate it and join() it before exiting. While it always seems to stop on my Linux system, MacOS X behaviour may be different.

Python works well enough with threads :-)

Update: You could try using subprocess, setting up the child process so that file handles are not inherited, and setting the child's stdin to subprocess.PIPE.