Re: Linux v2.6.9 and GPL Buyout

[John Alvord]

On Wed, 20 Oct 2004 00:18:25 -0400, Lee Revell <rlrevell@xxxxxxxxxxx>
wrote:

>On Tue, 2004-10-19 at 23:45, Ryan Anderson wrote:
>> RCU - originally a paper, implemented in Dynix and in other operating
>> systems from the paper (and patent), implemented in Linux as well.
>
>You could also make a strong argument that that patent is invalid
>because RCU is obvious.  I was doing this with perl and SQL before I
>ever heard of RCU.  If you don't want to lock a table (or didn't realize
>SQL had such a thing as table locking :-) you just fetch a value, make
>some calculation on it, then do the update iff that value has not
>changed.  If it has changed you fetch the new value and go back to step
>1.  It's just the obvious way to update a shared data structure if you
>have cmpxchg but no locking.

1972, IBM S/370 instruction set, CS Compare and Swap (32 bits) and CDS
Compare Double and Swap (64 bits), atomic compare and replace if test
equal. The Principles of Operation book even had sample code...

john alvord
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