(j3.2006) LOCK/UNLOCK question

[dick.hendrickson at att.net]

  -------------- Original message from Bill Long <longb at cray.com>: --------------


> It is possible to have a clue-limited programmer who would put a lock in 
> one function and an unlock for the same variable in a different 
> function, and then write a statement that executes both functions.
> 

Actually, that's probably already illegal.  I think the no-side-effects-on-
the-same-statement rule in section 7 would also apply to lock variables.


> However, it is also possible (and more likely) for a programmer to write 
> a function with both the lock and unlock, in the right order, and 
> serving a useful purpose.
> 
> I'd lean towards letting the second programmer do the useful thing at 
> the expense of having to tell the first programmer that he has written a 
> badly designed program.
> 
But it's more than just telling him it's badly designed.  You've got to 
get the words right to define all of the illegal (not unwise) cases.  I
think it's harder than just adding LOCK/UNLOCK to the paragraph
in question.  

I don't think it's totally unreasonable to acquire a lock in one routine and
release it in another.  I can even imagine using a lock variable that is never
unlocked as a "control construct" to set up an execute only once on whatever
image gets here first block of code.  

Dick Hendrickson 
> Cheers,
> Bill
> 
> 
> 
> 
> 
> dick.hendrickson at att.net wrote:
> > 
> > 
> >     Isn't one big difference that lock/unlock isn't a block construct. 
> >     If I understand
> >     it right, there's no requirement that the lock and unlock statement
> >     be in the
> >     same procedure.  [I don't even think you need an unlock statement.] 
> >     What would
> >     prevent the optimizer from invoking the procedure with the unlock
> >     first?  
> > 
> >     Dick Hendrickson
> > 
> > 
> -- 
> Bill Long                                   longb at cray.com
> Fortran Technical Support    &              voice: 651-605-9024
> Bioinformatics Software Development         fax:   651-605-9142
> Cray Inc., 1340 Mendota Heights Rd., Mendota Heights, MN, 55120
> 
> 
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