delphi xe TParallel.For的用法

unit Unit18;

interface

uses

System.SysUtils, System.Types, System.UITypes, System.Classes,

System.Variants,

FMX.Types, FMX.Controls, FMX.Forms, FMX.Graphics, FMX.Dialogs,

FMX.ScrollBox, FMX.Memo, FMX.Controls.Presentation, FMX.StdCtrls,

System.Threading, System.Diagnostics, System.SyncObjs;

//加黑的这三个单元需要手工加入,我想啊，如果代码中我写了TParallel.For能自动引用对应的单元就好了。

type

TForm18 = class(TForm)

btnForLoop: TButton;

btnParallelFor: TButton;

Memo1: TMemo;

procedure btnForLoopClick(Sender: TObject);

procedure btnParallelForClick(Sender: TObject);

private

{ Private declarations }

public

{ Public declarations }

end;

var

Form18: TForm18;

const

Max = 5000000;//计算1到Max间素数的个数.

function IsPrime(N: Integer): Boolean;//判断一个数是否为素数

implementation

{$R *.fmx}

//这是普通的实现方法，用For循环

procedure TForm18.btnForLoopClick(Sender: TObject);

var

I, Tot: Integer;

SW: TStopwatch;//秒表，计算耗用时间

begin

// counts the prime numbers below a given value

Tot := 0;

SW := TStopwatch.Create;

SW.Start;

for I := 1 to Max do

begin

if IsPrime(I) then

Inc(Tot);

end;

SW.Stop;

Memo1.Lines.Add(Format('Sequential For loop. Time (in milliseconds): %d - Primes found: %d',

[SW.ElapsedMilliseconds, Tot]));

end;

//这是用并行的实现方式

procedure TForm18.btnParallelForClick(Sender: TObject);

var

Tot: Integer;

SW: TStopwatch;

begin

try

// counts the prime numbers below a given value

Tot := 0;

SW := TStopwatch.Create;

SW.Start;

//这里用TParallel.For实现

TParallel.For(2, 1, Max,

procedure(I: Int64)

begin

if IsPrime(I) then

TInterlocked.Increment(Tot);//累计Tot的时候，做线程保护

end);

SW.Stop;

Memo1.Lines.Add(Format('Parallel For loop. Time (in milliseconds): %d - Primes found: %d',

[SW.ElapsedMilliseconds, Tot]));

except

on E: EAggregateException do

ShowMessage(E.ToString);

end;

//判断一个数是否为素数的函数

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.

来源：http://blog.sina.com.cn/s/blog_44fa172f0102w4tp.html

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