"""
Running this script triggers a race condition in the subprocess module.
There are 3 distinct behaviours:

(1) Terminate correctly
(2) Hang indefinitely
(3) Terminate, with exceptions such as

Exception in thread Thread-47:
Traceback (most recent call last):
  File "/usr/lib/python2.4/threading.py", line 442, in __bootstrap
    self.run()
  File "popen_bug.py", line 53, in run
    pipe.wait()
  File "/usr/lib/python2.4/subprocess.py", line 1007, in wait
    pid, sts = os.waitpid(self.pid, 0)
OSError: [Errno 10] No child processes

I have observed this on the following platforms :

Python 2.4.3 (#1, Jan 10 2007, 17:25:58) 
[GCC 3.4.6 20060404 (Red Hat 3.4.6-3)] on linux2

and

Python 2.4.4 (#1, Jan 30 2007, 09:52:03) 
[GCC 3.2.3 20030502 (Red Hat Linux 3.2.3-56)] on linux2

The script was originally written by Taale Skogan as a problem in popen2.
Test this module instead with the -p option. I have reproduced this
once with Python 2.4.4 but it's much harder to reproduce than the subprocess
issue. According to him it was observed on

Python 2.3.3 (#1, Feb 10 2004, 17:28:29)
[GCC 3.2.3 20030502 (Red Hat Linux 3.2.3-24)] on linux2

and

Python 2.3.5 (#1, Mar 30 2005, 17:01:57)
[GCC 3.2.3 20030502 (Red Hat Linux 3.2.3-49)] on linux2

and

Python 2.4.1 (#1, Apr 15 2005, 12:58:11)
[GCC 3.2.3 20030502 (Red Hat Linux 3.2.3-34)] on linux2

and

Python 2.4.1 (#1, Apr 15 2005, 13:32:19)
[GCC 2.95.2 19991024 (release)] on sunos5


He also claims he got no error here on this platform:

Python 2.3.5 (#1, Apr  6 2005, 11:30:31)
[GCC 2.96 20000731 (Red Hat Linux 7.3 2.96-113)] on linux2

"""
import optparse
import popen2 
import sys
import threading


class test_popen2(threading.Thread):
    def __init__(self):
        threading.Thread.__init__(self)

    def run (self):
        for i in range(5):
            pipe = popen2.Popen4("ls > /dev/null")
            pipe.wait()
            
class test_subprocess(threading.Thread):
    def __init__(self):
        threading.Thread.__init__(self)

    def run (self):
        import subprocess
        for i in range(5):
            pipe = subprocess.Popen("ls > /dev/null", shell=True)
            pipe.wait()


def main(argv):
    """
    Provoke the Popen bug.
    """
    usage = "usage: %prog"
    parser = optparse.OptionParser(usage)
    parser.add_option("-n", action="store",type="int", dest="num_threads", help="start NUM_THREADS threads", default=50)
    parser.add_option("-p", action="store_false", dest="subprocess", help="Use popen2 instead of subprocess", default=True)

    (options, args) = parser.parse_args(argv)

    if options.subprocess:
        worker = test_subprocess
    else:
        worker = test_popen2

    for i in range(options.num_threads):
        t = worker()
        t.start ()
        
    print "Started %d threads" % options.num_threads


if __name__ == '__main__':
    main(sys.argv[1:])