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Using TParallel.For from the Parallel Programming Library

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Among all the features, the Parallel Programming Library (PPL) includes a new Parallel for loop that is easy to use.

The TParallel.For accepts anonymous methods in Object Pascal whereas in C++ you create an Iterator event function and pass that as part of the TParallel.For loop call.

The following example is intended to demonstrate how easy is to plug in the parallel loop. Particularly, it shows how to work out if a number is a prime number replacing the traditional for by the TParallel.For.

Object Pascal:

Here is a function to calculate a prime number:

 
function IsPrime(N: Integer): Boolean;
var
  Test, k: Integer;
begin
  if N <= 3 then
    IsPrime := N > 1
  else if ((N mod 2) = 0) or ((N mod 3) = 0) then
    IsPrime := False
  else
  begin
    IsPrime := True;
    k := Trunc(Sqrt(N));
    Test := 5;
    while Test <= k do
    begin
      if ((N mod Test) = 0) or ((N mod (Test + 2)) = 0) then
      begin
        IsPrime := False;
        break; { jump out of the for loop }
      end;
      Test := Test + 6;
    end;
  end;
end;

This is the traditional way to loop and check for the number of prime numbers between 1 and Max value. Each number is checked in sequence and the total stored into a variable (here Tot is an integer):

 
const
 Max = 5000000; // 5M
 
for I := 1 to Max do
 begin
   if IsPrime (I) then
     Inc (Tot);
 end;

Using the PPL, this can be achieved by replacing the for command with a call to the class function TParallel.For passing in the code as an anonymous method:

 
TParallel.For(1, Max, procedure (I: Integer)
 
 begin
   if IsPrime (I) then
     TInterlocked.Increment (Tot);
 end);

C++:

Here is a function to calculate a prime number:

bool TForm1::IsPrime(int N){
	int Test, k;
	bool aPrime;
	if (N <= 3){
	   return N > 1;
	}
	else if (((N % 2) == 0) || ((N % 3) == 0)){
		return false;
	}else{
		aPrime = true;
		k = (int)sqrt(N);
		Test = 5;
		while (Test <= k){
			if (((N % Test) == 0) || ((N % (Test + 2)) == 0)){
				aPrime = false;
				break; //jump out of the for loop
			}
			Test = Test + 6;
		}
		return aPrime;
	}
}

This is the traditional way to loop and check for the number of prime numbers between 1 and Max value. Each number is checked in sequence and the total stored into a variable (here Tot is an integer):

int Max=5000000;
Tot=0;
 
for (int I=1; I<=Max; I++) {
	if(IsPrime(I)){
		Tot++;
	}
}

Using the PPL, this can be achieved by replacing the for command with a call to the class function TParallel.For passing in the code as an iterator event:

void __fastcall TFormThreading::MyIteratorEvent(TObject *Sender,int AIndex)
{
	if(IsPrime(AIndex)){
		TInterlocked::Increment(Tot);
	};
}
TParallel::For(NULL,1,Max,MyIteratorEvent);

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