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{ Example for a parallel loop with MTProcs.
Copyright (C) 2017 Mattias Gaertner mattias@freepascal.org
This library is free software; you can redistribute it and/or modify it
under the terms of the GNU Library General Public License as published by
the Free Software Foundation; either version 2 of the License, or (at your
option) any later version with the following modification:
As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent modules,and
to copy and distribute the resulting executable under terms of your choice,
provided that you also meet, for each linked independent module, the terms
and conditions of the license of that module. An independent module is a
module which is not derived from or based on this library. If you modify
this library, you may extend this exception to your version of the library,
but you are not obligated to do so. If you do not wish to do so, delete this
exception statement from your version.
This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public License
for more details.
You should have received a copy of the GNU Library General Public License
along with this library; if not, write to the Free Software Foundation,
Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
}
program parallelloop_nested1;
{$mode objfpc}{$H+}
{$ModeSwitch nestedprocvars}
uses
{$IFDEF UNIX}
cthreads, cmem,
{$ENDIF}
Classes, SysUtils, Math, MTProcs;
function FindBestParallel(aList: TList; aValue: Pointer): integer;
var
BlockSize: PtrInt;
Results: array of integer;
procedure InParallel(Index: PtrInt; Data: Pointer; Item: TMultiThreadProcItem);
var
i, StartIndex, EndIndex: PtrInt;
begin
Results[Index]:=-1;
StartIndex:=Index*BlockSize;
EndIndex:=Min(StartIndex+BlockSize,aList.Count);
//if MainThreadID=GetCurrentThreadId then
// writeln('FindBestParallel Index=',Index,' StartIndex=',StartIndex,' EndIndex=',EndIndex);
for i:=StartIndex to EndIndex-1 do begin
if aList[i]=aValue then // imagine here an expensive compare function
Results[Index]:=i;
end;
end;
var
Index: integer;
BlockCount: PtrInt;
begin
ProcThreadPool.CalcBlockSize(aList.Count,BlockCount,BlockSize);
SetLength(Results,BlockCount);
//writeln('FindBestParallel BlockCount=',BlockCount,' List.Count=',aList.Count,' BlockSize=',BlockSize);
ProcThreadPool.DoParallelNested(@InParallel,0,BlockCount-1);
// collect results
Result:=-1;
for Index:=0 to BlockCount-1 do
if Results[Index]>=0 then
Result:=Results[Index];
end;
function FindBestSingleThreaded(List: TList; Value: Pointer): integer;
var
i: integer;
begin
Result:=-1;
i:=0;
while i<List.Count do begin
if List[i]=Value then // imagine here an expensive compare function
Result:=i;
inc(i);
end;
end;
var
List: TList;
i: Integer;
begin
List:=TList.Create;
for i:=0 to 100000000 do
List.Add(Pointer(i));
writeln('searching ...');
i:=FindBestParallel(List,Pointer(List.Count-2));
writeln('parallel search i=',i);
i:=FindBestSingleThreaded(List,Pointer(List.Count-2));
writeln('linear search i=',i);
end.
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