Martin Panter added the comment:
Yes it looks like you might be right about those hanging buildbots. The
occasional successes (e.g.
<http://buildbot.python.org/all/builders/s390x%20Debian%202.7/builds/205/steps/test/logs/stdio>)
seem to happen when test_thread runs before any of the TK, TCL, and Idle tests.
The reason why this does not affect Python 3 is probably because the test only
calls sys.exit() in Python 2; this code was added in r78527. In Python 3, the
code was merged in revision 58c35495a934, but the code was apparently changed
to call os._exit() at the same time. So one potential fix or workaround could
be to change to os._exit() as in child-exit.patch.
It seems Tcl_FindExecutable() creates a thread, and this thread survives
fork(). (Perhaps it is re-created?) Python exiting does not cause this thread
to be stopped. Playing with “strace” it seems the threads that return from
fork() in the parent and child both finish with _exit(0). However the “main”
thread in the parent finishes with exit_group(0), which is documented as
terminating all threads. Calling os._exit() also seems to call exit_group(),
which explains why that fixes the problem in the child.
I can produce the problem in all versions of Python without using _tkinter,
using the following code instead:
import _thread, os, time
def thread1():
pid = os.fork()
if not pid:
# In the child, the original main thread no longer exists. Start a
# new thread that will stall for 60 s.
_thread.start_new_thread(time.sleep, (60,))
_thread.start_new_thread(thread1, ())
time.sleep(2) # Give fork() a chance to run
I’m not really sure, but maybe Python could improve its handling of this case,
when fork() is called on a non-“main” thread and another thread is also running
in the child process.
----------
keywords: +patch
Added file: http://bugs.python.org/file42053/child-exit.patch
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<http://bugs.python.org/issue26456>
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