Re: Asynchronous IO

[nasser@apldbio.com (Nasser Abbasi)]

>      From: ohk@edeber.nta.no (Ole-Hjalmar Kristensen FOU.TD/DELAB)

>I am not concerned about concurrent access to the same resource
>(file), but if Ada gives you any guarantees about the degree of
>parallellism if 2 tasks try to access 2 *different* files at the same
>time

... snip..

>After having said this, it occurs to me that the RM cannot make this
>mandatory, as not all environments in which Ada will run has the
>necessary facilities available, I suppose.....

Thats true.  I think I read somewhere on the net a while ago that
GNAT default scheduling policy for a task is run-till-blocked, but
if the platform has its own implementations of threads (as OS/2 threads,
SOlaris, NT et...) then Ada tasks are mapped to the system
threads, and the policy changes, so I guess the degree of parallellism
would depends on the platform. 

one the other hand, there is a paper about GNARL , (the Gnu Ada Runtime 
Library) has as one of its components the Pthreads layer (Posix threads), 
where tasks are implemented as pthreads. So that would be the
place I would think to look to determine the "degree" of
parallellism. GNARL interfaces with Pthreads to requests tasking
services. Offcourse this is on platforms that has Pthreads on it.

GNARL looks like this (from the GNARL paper)

        +--------------------------------+  
        |    Ada program                 |
        +---------------+----------------+
        |               |                |
        |               | Timer services |
        |               +----------------+
        | Ada-run time layer             |
        |                                |
        +--------------------------------+
        |   Gnu low-level layer          |
        +--------------------------------+
        |   Pthreads Layer               |
        +--------------------------------+
        |       OS                       |
        +--------------------------------+
        |     Machine                    |
        +--------------------------------+

I talk too much, I better shut up.
bye,
Nasser
-- 
Nasser Abbasi. C/C++/Ada Solaris. GeneAssist - A client/server 
application for Nucleic acid and protein sequence search and analysis.
PE-Applied BioSystem division. email:  nasser@apldbio.com   
MSEE, MSCS, MSCE, FM (and Karpov is my chess hero! ..).