Re: Assuming that TAS() will succeed the first time is verboten - Mailing list pgsql-hackers

From Tom Lane
Subject Re: Assuming that TAS() will succeed the first time is verboten
Date
Msg-id 9850.978067943@sss.pgh.pa.us
Whole thread Raw
In response to Re: Assuming that TAS() will succeed the first time is verboten  (Alfred Perlstein <bright@wintelcom.net>)
Responses Re: Assuming that TAS() will succeed the first time is verboten  (Bruce Momjian <pgman@candle.pha.pa.us>)
List pgsql-hackers
Alfred Perlstein <bright@wintelcom.net> writes:
> One trick that may help is calling sched_yield(2) on a lock miss,
> it's a POSIX call and quite new so you'd need a 'configure' test
> for it.

The author of the current s_lock code seems to have thought that
select() with a zero delay would do the equivalent of sched_yield().
I'm not sure if that's true on very many kernels, if indeed any...

I doubt we could buy much by depending on sched_yield(); if you want
to assume POSIX facilities, ISTM you might as well go for user-space
semaphores and forget the whole TAS mechanism.
        regards, tom lane


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