(j3.2006) LOCK/UNLOCK question

[Aleksandar Donev]

Malcolm Cohen wrote:

> "During an execution of a statement that invokes more than one
> procedure, at most one invocation shall cause execution of an image
> control statement other than CRITICAL or END CRITICAL."
> 
> I am puzzled as to why this doesn't allow LOCK/UNLOCK, since these are
> data-object equivalents to CRITICAL/END-CRITICAL. Yes this is only
> "good" if the LOCK/UNLOCK are either correctly "paired" within each
> procedure or if they operate on disjoint locks
By good do you mean "legal"? We can and perhaps should allow LOCK/UNLOCK 
as well, but then there is the danger that someone may in fact write 
code where the correct functioning depends on the procedures being 
executed in the same order on all images, which we do not want to 
guarantee. What rule tells that user that his code is "not good"? Either 
we should give proper semantics, in which case we tell the compilers to 
disable optimizations (or some such), or we need some additional 
constraints/restrictions.

As an aside, I argued and still believe that we need a CRITICAL(lock) 
construct for exactly these sort of reasons. I was not at the J3 meeting 
where my proposal was rejected so I do not know the reasons, but given 
that proposal was rejected my suggestion is to keep things "safe" and 
keep the existing text.

 > An oversight? Deliberate?
I seem to recall a direct discussion of this point at the last meeting 
but am not certain. I am cc'ing Nick since he was also there and may 
care about this issue.

Best,
Aleks

-- 
Aleksandar Donev, Ph.D.
Lawrence Postdoctoral Fellow @ LLNL
High Performance Computational Materials Science and Chemistry
E-mail: donev1 at llnl.gov
Phone: (925) 424-6816  Fax: (925) 423-0785
Address: P.O.Box 808, L-367, Livermore, CA 94551-9900
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