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Re: Assuming that TAS() will succeed the first time is verboten

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Alfred Perlstein <bright(at)wintelcom(dot)net>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Assuming that TAS() will succeed the first time is verboten
Date: 2001-01-02 07:59:20
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Lists: pgsql-hackers
> Alfred Perlstein <bright(at)wintelcom(dot)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.

Another issue is that sched_yield brings in the pthreads library/hooks
on some OS's, which we certainly want to avoid.

  Bruce Momjian                        |
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