libpthread/fork issue

Julian Elischer julian at
Sun Mar 9 16:36:01 UTC 2008

Bernd Walter wrote:
> On Fri, Mar 07, 2008 at 11:08:50AM -0500, Daniel Eischen wrote:
>> On Thu, 6 Mar 2008, Marko, Shaun wrote:
>>> I'm working on FreeBSD 6.2 and I'm wondering if anybody can help with an
>>> issue I've found using fork and threads. The attached program
>>> demonstrates the problem. In short, if a process creates a thread, joins
>>> the thread, then forks a child process which creates a thread, the
>>> child's attempt to create a thread will cause the program to dump core
>>> with the following error message:
>>> Fatal error 'mutex is on list' at line 540 in file
>>> /usr/src/lib/libpthread/thread/thr_mutex.c (errno = 0).
>> You are not allowed by POSIX to call any non-async-signal-safe
>> function from a child of a threaded program.  There's words
>> or rationale to the effect that the only purpose for forking
>> from a threaded program should be to call one of the exec*
>> functions.  Trying to create a thread from a child (like
>> you are trying to do) is definitely not supported.
> I've often done it, but since this is subject right now it is a good
> point to ask if I just had luck so far.
> Is it allowed to use popen(3) from a threaded programm?

"probably".. the child in popen does an exec.

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