Re: furwocks: Fast Userspace Read/Write Locks

["H. Peter Anvin" <hpa@zytor.com>]

Followup to:  <E16j95K-00047G-00@wagner.rustcorp.com.au>
By author:    Rusty Russell <rusty@rustcorp.com.au>
In newsgroup: linux.dev.kernel
> 
> > I m not in favor of that. The dominant lock will be mutexes.
> 
> To clarify: I'd love this, but rwlocks in the kernel aren't even
> vaguely fair.  With a steady stream of overlapping readers, a writer
> will never get the lock.
> 

Note that there really are two kinds of rwlocks: rwlocks with read
priority, and rwlocks with write priority.  They're actually fairly
different operations.  I guess one can envision other schemes, too,
but that's the main distinction.

Neither is particularly hard to implement, however, it's probably
better if they are considered different types (perhaps we can call the
ones with write priority "wrlocks" instead of "rwlocks").

	-hpa
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