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Date: Fri, 18 Jul 2025 09:51:11 +0200
To: cygwin AT cygwin DOT com
Subject: Re: Calling system() in multi-threads.
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From: Corinna Vinschen via Cygwin <cygwin AT cygwin DOT com>
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On Jul 18 00:44, Takashi Yano via Cygwin wrote:
> On Thu, 17 Jul 2025 17:19:49 +0200
> Corinna Vinschen wrote:
> > On Jul 17 23:14, Takashi Yano via Cygwin wrote:
> > > Hi Corinna,
> > > 
> > > On Wed, 16 Jul 2025 17:36:42 +0200
> > > Corinna Vinschen wrote:
> > > > On Jul 16 23:52, Takashi Yano via Cygwin wrote:
> > > > > Do you have any idea?
> > > > 
> > > > Locking would be super-simple.
> > > > 
> > > > But theoretically it should be possible to use a local child_info_spawn
> > > > variable at this point.  The ch_spawn child_info_spawn instance is not
> > > > copied to the child anyway, so that should be safe.  The same goes for
> > > > posix_spawn() then, btw.
> > > > 
> > > > I checked the sources and I don't see any dependency to ch_spawn
> > > > from a spawning process, in contrast to an exec'ing process.  That
> > > > doesn't mean there is none, just that I didn't find any.
> > > 
> > > Thanks!
> > > As a starting point, I tried tntroducing locking. It almost works
> > > as expected, however, sometimes my STC in my first report is hangs
> > > if N is large e.g. 100. The patch is as attached.
> > > 
> > > What am I missing?
> > 
> > I don't know.  You're perhaps not releasing the lock in all cases.
> > But I would have to debug this just like you ¯\_(ツ)_/¯
> > 
> > Out of curiosity, did you try using a locale child_info_spawn instance
> > instead?  That would be a rather nice solution, but I'm pretty sure
> > there's some other problem lurking in the dark...
> 
> I'm not sure what to do with local child_info_spawn.
> Some of other modules refer to ch_spawn, such as exception.cc and
> pinfo.cc. Also, has_execed* uses ch_spawn. What should we do for that?

Yes, that's what I meant with my above paragraph, i.e.

> > > > I checked the sources and I don't see any dependency to ch_spawn
> > > > from a spawning process, in contrast to an exec'ing process.  That
> > > > doesn't mean there is none, just that I didn't find any.

These external dependencies *should* only be of interest when performing
an execve, but not when performing a spawnve.


Corinna

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