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.
Ken
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