Re: GNAT's Protected Objects

[Maciej Sobczak <see.my.homepage@gmail.com>]

On 8 Lis, 21:34, Jeffrey Carter <spam.jrcarter....@spam.not.acm.org>
wrote:

> 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.

The protected object is shared between tasks and this sharing forces
the cache to flush and synchronize between cores (or CPUs). Note that
cache operates on entire blocks, which adds to the cost of data
transfer. If you measure the CPU utilization, you will probably see
that it is mostly idle during this test. Adding more CPUs will only
make things worse.

In other words, you have hoped for increased performance thanks to
additional computing resources, but you lost more on communication
between them.

The first version scales better, because it shares less (less often).

--
Maciej Sobczak * http://www.inspirel.com