Bug in fork() while in a thread

Jason Curl j.m.curl@gmx.de
Sat Aug 21 09:32:00 GMT 2010

Corinna Vinschen <corinna-cygwin <at> cygwin.com> writes:
> On Aug 15 14:53, Christopher Faylor wrote:
> > On Sun, Aug 15, 2010 at 07:42:01PM +0200, Jason Curl wrote:
> > >Is it allowed to issue the fork() system call while not in the main 
> > >thread? When I read the OpenGroup specifications I don't seem to find 
> > >anything against allowing this.
> > If I'm reading this correctly then "the stack" in this case is the stack
> > associated with the main thread.  Cygwin only duplicates the stack in
> > the executing thread.  In your example, env (or presumably env2) from
> > the main thread is passed to another thread which then calls fork.  In
> > that scenario, the forked process is going to see garbage in env since
> > the array has never been initialized.
> I guess I'm missing something here.  Here's an excerpt from the SUSv4
> fork man page:
>   The fork() function shall create a new process. The new process (child
>   process) shall be an exact copy of the calling process (parent process)
>   except as detailed below:
>   [...]
>   o A process shall be created with a single thread. If a
>     multi-threaded process calls fork(), the new process shall contain
>     a replica of the calling thread and its entire address space,
>     possibly including the states of mutexes and other resources.
>     [...]
> Is the stack of another thread, which is not executed in the forked
> process anymore, a part of the calling's thread "entire address space"?

Open Group Posix.1c-2004 mentions only a "signal stack" doesn't need to be 
copied for XSI.

Linux & FreeBSD 7.0 work OK. QNX641 returns ENOSYS if it even sniffs a thread 
call. I haven't tested Solaris Sparc. 

Which standard is Cygwin "closest" to, that I can use as a reference when I 
trip up on similar problems? I have the hint the SuSv4 implementation of Posix.

Thanks for your wonderful support.

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