[Python-Dev] Python threads end up blocking signals in subprocesses

Jeff Epler jepler at unpythonic.net
Wed Dec 17 18:31:26 EST 2003

On Wed, Dec 17, 2003 at 09:14:50AM -0600, Jeff Epler wrote:
> There are also problems on redhat9, where signals in a fork+exec'd
> subprocess are blocked, for instance.  This seemed to be a consequence
> of blocking all signals in thread_pthread.h:PyThread_start_new_thread().

To follow up on my own message, here is a program that demonstrates the
problem I ran into with threads and signals.

doit() uses system() to create a process that should kill itself with a
signal nearly instantly, otherwise it sleeps for one second.  If doit()
is called from the main thread or before any threads are created, it
prints a time well under 1 second.  If it is run from a thread, it takes
just over a second, because the delivery of the signal in the subprocess
is blocked.

Typical output:
	$ python thread-signal-problem.py 
	not threaded
	Elapsed time 0.00420594215393
	Elapsed time 1.00974297523
	main thread
	Elapsed time 0.00419104099274

import thread, time, os

def doit():
	t = time.time()
	os.system("kill $$; sleep 1")
	t1 = time.time()
	print "Elapsed time", t1-t

print "not threaded"
print "subthread"
thread.start_new(doit, ())
print "main thread"

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