[fpc-devel] Suggestion: reference counted objects

[Michael Schnell]

On 09/26/2014 06:06 PM, Mark Morgan Lloyd wrote:
> Different implementations could potentially use either local threads 
> or OpenMPI.
Yep.
With "Local Thread" you supposedly mean user land threads. Same would 
need to be implemented together with an appropriate set of synchronizing 
functions. Seems like a huge effort (in fact a complete preemptive 
multitasking OS running in user land)

I suppose there are several ways to implement OpenMP.

>
>> Same could be accessible by the user for more complex stuff and be 
>> used as the infrastructure of a parallel loop syntax.
>
> Agreed, but a good starting point would be working out how to map a 
> sequential (non-reentrant) block syntax onto e.g. the existing 
> critical section class.
>

Hmm

As "easy to use" syntax I meant simple stuff that don't need explicit 
critical sections but just a means to hold the main line code until the 
spawned  parallel processing is ready. I understand in Prism this is 
done with "future" variable, but I don't know how they are used.

Something like this to do a matrix multiplication

parallel for i := 0 to m-1 do begin
   parallel for j = 0 to n-1 do begin
     r := 0;
for k := 0 to n-1 do begin
       r := r + x[k,j] * y[i,k];
     end;
     z[i,j] = r
   end;
end;
future Z;
z[0,0]:=Z[0,0]+1;


(or similar :-) )

Here, obviously Z needs to be defined as a "future" that is available 
not before all instances of the parallel loops are done.

The compiler magic and library would need to take care of launching an 
appropriate count of threads (about as many as the count of processors 
available in hardware).

-Michael