GNAT's Protected Objects

[Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org>]

I was trying to decide the "optimal" number of tasks for concurrent problems on 
my 2-core system, so I wrote a little program to do matrix multiplication with 
multiple tasks.

When the tasks divide the result matrix among themselves in the obvious way, 
there's a clear decrease in elapsed time as the number of tasks increases to 4.

If I use a Linda-like approach, with a protected procedure doling out (Row, 
Column) pairs on demand, a single task is always fastest, and using multiple 
tasks slows things down. This wasn't what I expected, and wondered if this is 
inherent in such an approach, or specific to GNAT's way of implementing 
protected objects.

-- 
Jeff Carter
"Sir Robin the not-quite-so-brave-as-Sir-Lancelot,
who had nearly fought the Dragon of Angnor,
who nearly stood up to the vicious Chicken of Bristol,
and who had personally wet himself at the
Battle of Badon Hill."
Monty Python & the Holy Grail
68