wait() on Popen4 object from thread?

[Grant Edwards]

I'm having problems calling the Popen4 object wait() method
from a thread.  The folloing program produces an error on some
machines (but seems to work on others)

------------------------------8<------------------------------
import time
import threading
import popen2

def monitorThread():
    while True:
        s = p.fromchild.readline()
        if s:
            print s
        else:
            print p.wait()
            watching = False
            break

watching = True    
p = popen2.Popen4('mplayer -quiet -slave  test.avi')
threading.Thread(target=monitorThread).start()

while watching:
    time.sleep(0.1)

------------------------------8<------------------------------

   Exception in thread Thread-1:
   Traceback (most recent call last):
     File "/usr/lib/python2.4/threading.py", line 442, in __bootstrap
       self.run()
     File "/usr/lib/python2.4/threading.py", line 422, in run
       self.__target(*self.__args, **self.__kwargs)
     File "testit.py", line 11, in monitorThread
       print p.wait()
     File "/usr/lib/python2.4/popen2.py", line 94, in wait
       pid, sts = os.waitpid(self.pid, 0)
   OSError: [Errno 10] No child processes
   
   
Is it a requirement that the Popen4 object's wait method be
called from the same thread that created it?

Why does it work on one machine:

   Python 2.4.2 (#1, May  7 2006, 17:58:05) 
   [GCC 3.4.5 (Gentoo 3.4.5-r1, ssp-3.4.5-1.0, pie-8.7.9)] on linux2
   Type "help", "copyright", "credits" or "license" for more information.

But not on another:

   Python 2.4.2 (#1, May  7 2006, 17:34:02) 
   [GCC 3.4.5 (Gentoo 3.4.5-r1, ssp-3.4.5-1.0, pie-8.7.9)] on linux2
   Type "help", "copyright", "credits" or "license" for more information.


-- 
Grant Edwards
grante at visi.com