Date: Thu, 18 Sep 2008 17:03:46 -0400 (EDT) From: Daniel Eischen <deischen@freebsd.org> To: David Naylor <naylor.b.david@gmail.com> Cc: Tom Evans <tevans.uk@googlemail.com>, freebsd-current@freebsd.org Subject: Re: FreeBSD deadlock (with fork?) Message-ID: <Pine.GSO.4.64.0809181702500.20788@sea.ntplx.net> In-Reply-To: <200809181927.52384.naylor.b.david@gmail.com> References: <200809180631.47071.naylor.b.david@gmail.com> <200809181857.25872.naylor.b.david@gmail.com> <Pine.GSO.4.64.0809181308140.19815@sea.ntplx.net> <200809181927.52384.naylor.b.david@gmail.com>
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On Thu, 18 Sep 2008, David Naylor wrote: > On Thursday 18 September 2008 19:13:19 Daniel Eischen wrote: >> On Thu, 18 Sep 2008, David Naylor wrote: >>> On Thursday 18 September 2008 15:33:52 Tom Evans wrote: >>>> On Thu, 2008-09-18 at 06:31 +0200, David Naylor wrote: >>>>> Hi, >>>>> >>>>> I have a program that spawns a lot of subprocesses (with pipes open) >>>>> from multiple threads. The problem is the program often deadlocks, but >>>>> not consistently. Sometimes the program can run over 5 times to >>>>> competition without incidence and yet othertimes it locks within a few >>>>> seconds. >>>> >>>> Do you create threads, which then fork(), or do you fork() and then >>>> create threads? >>> >>> I have many threads that then fork. (aka forking threads). >>> >>>> I think the former will not work.. >>> >>> Is there any reason for this and is this a FreeBSD limitation or a >>> general problem? >> >> No, the former will work. You can fork() from threads, only as long >> as your forked processes only call async-signal-safe functions or >> some form of exec(). For instance, you can't fork and then create >> new threads from that child process. If you are not immediately >> exec()'ing from the child process, then you have to be careful >> and only use async-signal-safe functions. >> >> Remember that you have multiple threads in the parent, so the >> state of libthr, libc, etc may be inconsistent in a child >> process. > > If you have a look at the backtrace from my original post you will see that > all my threads are getting locked. The program I am using is python and the > call that is forking is Popen(['some', 'program'], stdout=PIPE, > stderr=STDOUT). As far as I know it just sets up the pipes and does an > execvp. (See > http://svn.python.org/view/*checkout*/python/tags/r252/Lib/subprocess.py?content-type=text%2Fplain&rev=60915 > from line 981 to 1091). [[I tried appending close_fds=True to the argument, > it appeared to make the program deadlock less often...]] > > Any ideas as to what might be causing this dead lock (and why all the threads > are stopping in amd64 specific assembler)? No, could be a bug in python though. -- DE
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