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1 unit Unit1; 2  3 interface 4  5 uses 6   Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics, 7   Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls; 8  9 type10   TMyThread = class(TThread)//自定义的线程11   protected12     procedure Execute; override;13   end;14 15   TForm1 = class(TForm)16     Button1: TButton;17     procedure Button1Click(Sender: TObject);18   private19     {
      Private declarations }20   public21     {
      Public declarations }22   end;23 24 var25   Form1: TForm1;26   mytd: TMyThread;//线程对像27 implementation28 29 {
     $R *.dfm}30 31 //返回值：0-已释放；1-正在运行；2-已终止但未释放；3-未建立或不存在32 function CheckThreadFreed(aThread: TThread): Byte;33 var34   I: DWord;35   IsQuit: Boolean;36 begin37   if Assigned(aThread) then38   begin39     IsQuit := GetExitCodeThread(aThread.Handle, I);40     if IsQuit then //If the function succeeds, the return value is nonzero.41     //If the function fails, the return value is zero.42     begin43       if I = STILL_ACTIVE then //If the specified thread has not terminated,44       //the termination status returned is STILL_ACTIVE.45       Result := 146     else47       Result := 2; //aThread未Free，因为Tthread.Destroy中有执行语句48     end49     else50     Result := 0; //可以用GetLastError取得错误代码51   end52   else53   Result := 3;54 end;55 56 procedure TMyThread.Execute;57 var58  I: Integer;59 begin60   for I := 0 to 500000 do61   begin62     Form1.Canvas.Lock;63     Form1.Canvas.TextOut(10, 10, IntToStr(I));64     Form1.Canvas.Unlock;65   end;66 end;67 68 procedure TForm1.Button1Click(Sender: TObject);69 begin70   if CheckThreadFreed(mytd)<>1 then //判断线程是否存在71   begin72     mytd := TMyThread.Create(True);73     mytd.FreeOnTerminate := True;74     mytd.Resume;75   end;76 end;77 78 end.