[Moving this discussion to cygwin-developers]

Hi Ken,

On Jul 31 10:10, Corinna Vinschen wrote:
> On Jul 30 19:04, Ken Brown via Cygwin wrote:
> > Hi Corinna,
> > 
> > On 7/30/2020 1:17 PM, Corinna Vinschen wrote:
> > > Hi Ken,
> > > 
> > > On Jul 30 13:59, Corinna Vinschen wrote:
> > > > On Jul 29 19:12, Ken Brown via Cygwin wrote:
> > > > > On 7/29/2020 4:17 PM, Ken Brown via Cygwin wrote:
> > > > > > posix_spawn(p) returns before the spawned process is fully up and
> > > > > > running.  [...]
> > > > > I just took a look at the source, and I see that posix_spawn was taken from
> > > > > FreeBSD.  Does FreeBSD have the same problem?  Should applications just be
> > > > > aware of this issue and insert a sleep after posix_spawn before sending
> > > > > signals?
> > > > 
> > > > Actually, this is a Cygwin problem.  I just had a look into the
> > > > newlib implementation myself, and it turns out that the code,
> > > > in particular the do_posix_spawn() function, is BSD specific.  It
> > > > relies on the BSD implementation of vfork(2).  Cygwin's vfork(2)
> > > > on the other hand, is NOT following the historic idea of the
> > > > BSD vfork(2), rather it's equivalent to fork(2).  This is
> > > > POSIX compliant, but certainly the reliance of the BSD vfork
> > > > behaviour makes do_posix_spawn() as it's implemented right now,
> > > > not overly functional for Cygwin.
> > > > 
> > > > IOW, we need a Cygwin-specific do_posix_spawn() using fork(2)
> > > > in conjunction with some synchronization the BSD function
> > > > gets "for free" by using its specific vfork(2).
> > > 
> > > Below is a POC implementation for a Cygwin-specific do_posix_spawn().
> > > If this does the trick (at least your testcase works in my testing),
> > > then I'm planning to move the function over to the winsup/cygwin dir
> > > so it can be streamlined further.
> > > 
> > > Can you give it a try?
> > 
> > It looks like something further is needed: 'wait' doesn't seem to recognize
> > the spawned process.
> 
> Oh well.  I did a quick test with your new testcase (thanks for that!)
> and it seems to be a bit more complicated than I anticipated yesterday.
> The parent-child relationship between the processes is broken.  I have
> to think a while about this problem, stay tuned.

I attached another patch.  This one is designed from the ground up and
I *think* it works as desired.  I added lots of comments so the idea
behind this patch should be clear enough.

Please give it a try.


Thanks,
Corinna