Re: Read/write locks

H. Peter Anvin (hpa@transmeta.com)
21 Sep 1997 07:20:47 GMT

Followup to: <199709210429.AAA28617@jenolan.rutgers.edu>
By author: "David S. Miller" <davem@jenolan.rutgers.edu>
In newsgroup: linux.dev.kernel
>
> An update lock lets you read the structure while guaranteeing it
> will not change, and also that you can upgrade it to a write lock
> without the structure changing.
>
> Perhaps I'm feeling dense this evening, but what in the world is the
> difference then between holding the update lock and holding a rwlock
> as a writer? I can't see it...
>

The way I read it, the "update lock" operation supports transitioning
from a read lock to a write lock guaranteeing that no other writers
can come in between, as you could if you just released the read lock
and grabbed a write one.

-hpa

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