Re: The "()" operator revisited.

["Robert I. Eachus" <rieachus@comcast.net>]

Robert A Duff wrote:

> Adjust gets control after the (old) left-hand side has been finalized.
> So, for example, how could ":=" reuse the space of the LHS?
> Also, what if you want the whole ":=" to be locked, rather than
> just part of it?

I have created types where exactly this locking is needed, and it is a 
royal pain. ;-)  The problem is not the calls to Adjust, it is that you 
can't be sure that a Finalize will have a matching Adjust call.  In 
particular you may have two Finalize calls per Adjust.  You end up 
keeping a stack of "unmatched" Finalize calls and using some heuristic 
to clean up.  I used an internal sequence number assigned by Initialize, 
and the address.  The lock on an address was started by a Finalize, and 
cleared by an Adjust.  All locks though had a timeout, or more actually, 
attempting to do a second Finalize of the same address resulted in a 
delay, not a busy wait.

It worked, but it felt kludgy.  I really wished we had four operations, 
one for the Finalize of the LHS, and another Finalize for all other cases.

-- 
                                           Robert I. Eachus

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