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Date:	Fri, 28 Aug 2020 10:35:51 +0200
From:	Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To:	cygwin AT cygwin DOT com
Subject:	Re: Sv: Limit for number of child processes
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On Aug 27 21:42, Ken Brown via Cygwin wrote:
> On 8/27/2020 8:17 AM, Kristian Ivarsson via Cygwin wrote:
> > Hi Corinna
> > 
> > > > Dear cygwin folks
> > > > 
> > > > It seems like there's a limit of the number of possible child
> > > > processes defined to 256 with 'NPROCS' in //winsup/cygwin/child_info.h
> > > > used in 'cprocs' in //winsup/cygwin/sigproc.cc
> > > > 
> > > > 256 is quite few possible children in an enterprise environment and
> > > > perhaps the limit should be limited by the physical resources or
> > > possibly Windows ?
> > > 
> > > The info has to be kept available in the process itself so we need this
> > > array of NPROCS * sizeof (pinfo).
> > > 
> > > Of course, there's no reason to use a static array, the code could just as
> > > well use a dynamically allocated array or a linked list.  It's just not
> > > the way it is right now and would need a patch or rewrite.
> > > 
> > > As for the static array, sizeof pinfo is 64, so the current size of the
> > > array is just 16K.  We could easily bump it to 64K with NPROCS raised to
> > > 1024 for the next Cygwin release, at least on 64 bit.
> > > I don't think we should raise this limit for 32 bit Cygwin, which is kind
> > > of EOL anyway, given the massive restrictions.
> > 
> > I don't know the exact purpose of this and how the cprocs is used, but I'd
> > prefer something totally dynamic 7 days out of 7 or otherwise another limit
> > would just bite you in the ass some other day instead ;-)
> > 
> > A linked list could be used if you wanna optimize (dynamic) memory usage but
> > an (amortized) array would probably provide faster linear search but I guess
> > simplicity of the code and external functionality is the most important
> > demands for this choice
> 
> Any change here (aside from just increasing NPROCS) would have to be done
> with care to avoid a performance hit.  I looked at the history of changes to
> sigproc.cc, and I found commit 4ce15a49 in 2001 in which a static array
> something like cprocs was replaced by a dynamically allocated buffer in
> order to save DLL space.  This was reverted 3 days later (commit e2ea684e)
> because of performance issues.

Yup, that's one of the problems to keep in mind.


Corinna

-- 
Corinna Vinschen
Cygwin Maintainer
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