Re: Question about concurrent access to array

[Adam Beneschan <adam@irvine.com>]

On Thursday, February 14, 2013 12:39:01 PM UTC-8, jo...@peppermind.com wrote:
> I'd like like several tasks to share an unpacked array of a definite discriminant record type.
> 
> 1.) Is this possible?

I don't see why it wouldn't be.

> 2.) Do I need any kind of synchronization if I can guarantee that every task can only write and read to a different area (different range of indices) in the array? 
> 
> Performance matters a lot in this case, which is why I would prefer not to use a protected object or any other synchronization mechanism. I can't imagine how a problem could occur if every task only accesses his own part of the array, but perhaps there is still one?

I'd use an alignment aspect (or representation clause) to make sure that the array elements are aligned on some boundary, probably based on the largest integer that your machine can deal with.  Otherwise there's the risk that two consecutive array elements that "belong" to different tasks might share part of a "word" (or something), and the code to write into an element might involve reading the entire word, modifying part of the word, then writing it back.  If you do this, then I don't see how there could be a problem.  But that doesn't mean there isn't one.

                             -- Adam