p5pRT
commented
21 years ago From Jens.Lippmann@t-mobile.de
Created by jens.lippmann@t-mobile.de
Hello!
I'm into Perl for more than 8 years and I cannot overemphasize that I appreciated every single minute programming with it.
Now\, I actually spent quite a large amount of time to find a nasty bug that crashes Perl on Windows NT when I call fork and exec. The problem is not related to any specific Perl but rather sticks to Perl ports that create threads instead of processes. As soon as the exec'd task terminates there is a considerable high chance (obviously a race condition) to crash perl. When I replace exec() with system() and exit() the problem pertains\, but not if I use system() and POSIX::_exit().
I am sending this bug report to the mainstream Perl development instead of any specific Win32 support group such as ActiveState or Indigo just because the 'bug' I am referring herein seems to be related in a deficient Perl documentation on this topic.
My pledge is to build up a FAQ topic (perldoc -q) for fork that helps out of this remedy\, and to extend the fork/exec sections in the perlfuncs doc module\, and to overhaul the notorious 'if ($pid = fork()) { ... } else { ... exec/exit; }' examples that are used throughout the perlipc doc.
It is generally a bad idea to use exit() after fork()\, unless you want to create a daemon process (see http://www.erlenstar.demon.co.uk/unix/faq_toc.html "1.1.3 Why use_exit rather than exit in the child branch of a fork?"). It is also a bad idea to use exec() after fork() on a Win32 port for the simple reason that exec() itself performs cleanup action on process termination similar to exit().
It is no good way to leave the user undocumented and let the developers run into the same obstacles again with every new release. Meanwhile there are half a dozen Win32 module extensions on CPAN\, but none seems to come with support throughout all Win32 platforms or availability for any perl distribution. For the sake of transparency and portability\, why can't Perl itself solve the exit handling to smooth out thread and non-thread forks? I recommend to either - keep the transparency of fork() but then make exit() transparent as well (i.e. remember the 'thread' state and act accordingly)\, or - do not support fork() on Win32 but vfork() and provide a function like vexit()
I further recommend to generally incorporate POSIX::_exit() into the Perl core and to add a hint about the batch command 'start' which can be used to conveniently spawn a task under Win32.
kind regards Jens Lippmann
toddr
Migrated from rt.perl.org#21382 (status was 'open')
Searchable as RT21382$