[Xr] Can the xrs argument be removed?

[Carl Worth]

On May 22, Bill Spitzak wrote:
 > I think only the pointer is thread-local. The XrState structure itself is in 
 > normal memory, so another thread could use it. Once the thread dies nothing 
 > can access the pointer, but if it's value was copied somewhere the XrState is 
 > still available.

Yes, of course. Thanks.

 > I think it would be a good idea to lock at the XrState level, so that only 
 > one thread can use an XrState at a time (I suspect this will avoid a lot of 
 > internal locking in XrState, but I may be wrong).

As is, the current implementation of Xr doesn't have any internal
locking. So right now, either only one thread uses an XrState at a
time, (which is not enforced), or locking is done externally.

The option above enforces the "one thread at a time" rule while
disallowing the external locking.

I'm not sure which scenario is preferable.

-Carl