become_daemon should use os._exit instead of sys.exit

[tclugg@…]

django.utils.daemonize.become_daemon forks then uses sys.exit(0) instead of os._exit(0), which can cause some nasty issues. os._exit is the correct way to exit after forking in Python, as os._exit avoids calling Python cleanup functions which may cause issues such as segfaults.

See ​http://docs.python.org/lib/os-process.html for details on os._exit().

[Chris Beaven]

Pushing to a design decision as it's over my head :)

[Malcolm Tredinnick]

This is only half right. The main parent should call sys.exit(), since it can be cleaned up normally; it's a normal short-lived process. The children should generally call os._exit() to avoid double cleanups via atexit() paths.

So I believe the first change is wrong and the second change is right, but I need to do some re-reading to confirm this.

[Leo Shklovskii]

Malcolm, you're right. The first exit() call is in the parent so it should stay exit(). The second call is in the first child, so _exit() is more appropriate. I've attached a patch only to correct the second one.

[Malcolm Tredinnick]

(In [7290]) Fixed #6175 -- Use os._exit() instead of sys.exit() in child processes. Based
on a patch from Tyson Clugg.

[durdinator]

Malcolm wrote:

So I believe the first change is wrong and the second change is right, but I need to do some re-reading to confirm this.

and Leo wrote:

Malcolm, you're right. The first exit() call is in the parent so it should stay exit().

But the patch actually committed changes both calls. Are you sure that's correct?

[Malcolm Tredinnick]

No it didn't. Have a look at the line numbers affected. The patch I committed was a variant on the two attached to these tickets and fixed a place that was overlooked in both those patches.

[durdinator]

Ah, I see. Glad to see it wasn't a mistake after all.