system() using vfork() or posix_spawn() and libthr

[Jilles Tjoelker]

On Tue, Aug 14, 2012 at 11:15:06PM +0800, David Xu wrote:
> But in real word, pthread atfork handlers are not async-signal safe,
> they mostly do mutex locking and unlocking to keep consistent state,
> mutex is not async-signal safe.
> The malloc prefork and postfork handlers happen to work because I have
> some hacking code in library for malloc locks. Otherwise, you even
> can not use fork() in signal handler.

This problem was also reported to the Austin Group at
http://austingroupbugs.net/view.php?id=62

Atfork handlers are inherently async-signal-unsafe.

An interpretation was issued suggesting to remove fork() from the list
of async-signal-safe functions and add a new async-signal-safe function
_Fork() which does not call the atfork handlers.

This change will however not be in POSIX.1-2008 TC1 but only in the next
issue (SUSv5).

A slightly earlier report http://austingroupbugs.net/view.php?id=18 just
requested the _Fork() function because an existing application
deadlocked when calling fork() from a signal handler.

-- 
Jilles Tjoelker