Re: POSIX.1 semaphores vs message queues

[Paul Goyette <paul%vps1.whooppee.com@localhost>]

On Sat, 7 Nov 2015, Joerg Sonnenberger wrote:

> On Sat, Nov 07, 2015 at 10:55:49AM +0800, Paul Goyette wrote:
> > I'd like to understand the rationale that makes POSIX sempahores a
> > non-optional component of the kernel, while POSIX message queues are
> > still optional.  Both seem to be related specifically to use in the
> > librt real-time library.
>
> Semaphores are used quite a lot and not only required by librt, but
> also by libpthread. I'm not sure what is using message queues.

Hmmm, sounds like a great reason to include the semaphore code in
every kernel by default.  But it doesn't sound sufficiently critical
to _prevent_ it from being removed from custom kernels if explicitly
requested by the user.

I'd like to suggest that this code once again become an option.  Rather
than adding an option to every kernel configuration file, however, we
can simply add it to src/sys/conf/std where it will get included by
default, in the same manner as MQUEUE.  (I also propose use of "option
SEMAPHORE" rather than P1003_1B_SEMAPHORE, similar to MQUEUE.)

There is nearly zero cost to existing users.  The only changes to any
existing kernels would be an additional line in the INCLUDE_CONFIG_FILE
text for the new line in src/sys/conf/std, and there would be a new file
(and directory) within /stand/<version>/modules/.  Builds would take a
very little bit longer to compile and link the new/resurrected module.



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