John M McIntosh wrote:
> 
> on 7/28/00 12:27 PM, Tim Rowledge at tim at sumeru.stanford.edu wrote:
> 
> > In message <3981D6C8.9639FE71 at bike-nomad.com>
> > Ned Konz <ned at bike-nomad.com> wrote:
> >
> >
> >> Does anyone know whether it's possible to signal an external
> >> Semaphore asynchronously? I looked at doing just this (including using SIGIO)
> >> for the Serial stuff, but didn't know how it would work.
> > You can use signalSemaphoreWithIndex asynchronously, but the semaphore
> > wil only get _actually_ signalled the next time checkForInterrupts is
> > called.
> >
> 
> Well... assuming signalSemaphoreWithIndex is perfectly interrupt safe is
> dangerous if you are driving it at a high interrupt rate from multiple OS
> threads. Right now it uses a non-atomic counter to track queued signals, if
> you hit things just right you could miss a signal. Also beware the table
> only holds 500 signals at time, so doing a burst of 1000 signals could be an
> issue.
> 
> In 2.8 I changed much of the code to fix some issues with how stuff gets
> deposited in the queue, versus how checkForInterrupts removes stuff from the
> queue, this solved most of the issues with lost signals, but to be *perfect*
> it would require the use of atomic operators to manage it's structure.


John,

What are atomic operators and why don't we currently have them in
there?  Are they not on all platforms?  I've actually not seen this
internal queue in the unix socket code as it relies on the os buffer for
any particular handle.

cheers,
Rob

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