Using MPICH2
lazarus / 5-Lazarus Extra Components

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Leledumbo · 2010-12-06 18:17

I'm currently playing with MPICH2 due to my parallel and concurrent
programming class. Is there anybody experienced on this? I'd like to
try doing some parallel operation over data allocated in an array, the
operation can be done in parallel, but the printing of the result is
not, and it has to be done when all processes have done their job. How
can I do this?

Here's what I've done so far:
Code: [Select]program MPISelectionSort;

{$mode objfpc}{$H+}
{$ifdef unix}
{$linklib c}
{$endif}

uses
  MPI;

const
  Max = 100;

type
  TData = array [0 .. Max - 1] of Integer;

var
  NProcs,ID,Count,i,j,Temp,Start,End_,Min: Integer;
  Data: TData;
begin
  MPI_Init(@argc,@argv);
  MPI_Comm_size(MPI_COMM_WORLD,@NProcs);
  MPI_Comm_rank(MPI_COMM_WORLD,@ID);
  for i := 0 to Max - 1 do
    Data[i] := Random(512) - 256;
  MPI_Bcast(@Data[0],Length(Data),MPI_INT,0,MPI_COMM_WORLD);
  Count := Max div NProcs;
  Start := ID * Count;
  End_  := Start + Count - 1;
  WriteLn('Count=',Count,',Start=',Start,',End=',End_);
  for i := Start to End_ - 1 do begin
    Min := i;
    for j := i + 1 to End_ do
      if Data[j] < Data[Min] then
        Min := j;
    Temp := Data[i];
    Data[i] := Data[Min];
    Data[Min] := Temp;
  end;
  MPI_Finalize;
  if ID = 0 then
    for i := 0 to Max - 1 do begin
      Write(Data[i]:5);
      if (i + 1) mod 10 = 0 then WriteLn;
    end;
end.
No, it's not yet correct. The master process could have written the
data before all other processes finish their job. And if I've managed
this, the sorting is still correct "locally", meaning that it's
correct only for a partition. For example, if I have 5 processes,
process with ID=0 is responsible to sort data from index 0 to 19 and
it should be correct for that index range (i.e. partition) only,
ignoring results from other partitions. Same things apply to other
partitions.