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Date: Tue, 4 Mar 2025 12:38:52 +0100
To: cygwin AT cygwin DOT com
Subject: Re: Cygwin 3.6: Supporting 128 POSIX realtime (SIGRTMAX-SIGRTMIN >=
 128) signals?
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From: Corinna Vinschen via Cygwin <cygwin AT cygwin DOT com>
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On Mar  4 12:20, Lionel Cons via Cygwin wrote:
> On Tue, 4 Mar 2025 at 11:08, Corinna Vinschen via Cygwin
> <cygwin AT cygwin DOT com> wrote:
> >
> > On Mar  3 23:07, Lionel Cons via Cygwin wrote:
> > > On Mon, 3 Mar 2025 at 12:43, Corinna Vinschen via Cygwin
> > > <cygwin AT cygwin DOT com> wrote:
> > > >
> > > > On Feb 28 15:36, Lionel Cons via Cygwin wrote:
> > > > > We've hit a scalability issue in Cygwin today, the application in
> > > > > question ran out of POSIX realtime signals (i.e. SIGRTMIN-SIGRTMAX).
> > > > >
> > > > > Could Cygwin support 128 POSIX realtime signals?
> > > >
> > > > Not possible.  sigset_t is an unsigned long, thus we can only support
> > > > up to 64 signals.
> > > >
> > > > A change to a bigger sigset_t is an ABI breakage and requires two
> > > > different entry points for all functions touching the sigset_t type, one
> > > > for the new definition of sigset_t, one for backward compatibility with
> > > > existing applications.  This *could* be part of 3.7, but I don't make
> > > > any promises.
> > >
> > > gcc has int128_t - would that help you?
> >
> > Not at all.  It doesn't change the underlying problem of the ABI breakage.
> 
> That is... bad.
> For the new ABI, maybe store a pointer to the byte array which holds
> the signal bits, and the array has a size prefix, so it can be
> extended on demand? Public functions only use pointer+size then...

It's not about how to do a new ABI.  It's about when and who does it.

- Very certainly not in 3.6.
- *Maybe* in 3.7.
- Do we have a volunteer creating a patch?


Corinna

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