unit fo_ThreadListDePraxis;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Generics.Collections,
  Vcl.Samples.Spin;

type
  TForm1 = class(TForm)
    laSleeptime: TLabel;
    Memo1: TMemo;
    Button1: TButton;
    Button2: TButton;
    SpinEdit1: TSpinEdit;
    Label1: TLabel;
    procedure Button1Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure FormClose(Sender: TObject; var Action: TCloseAction);
    procedure Button2Click(Sender: TObject);
    procedure SpinEdit1Change(Sender: TObject);
  private
    { Private-Deklarationen }
  public
    { Public-Deklarationen }
  end;

  TMyList = class(TList<Integer>)
  end;

  TMyThread = class(TThread)
  private
    FCounter, FSleepTime: Integer;
  protected
    procedure Execute; override;
  public
    property SleepTime: Integer read FSleepTime write FSleepTime;
  end;

var
  Form1: TForm1;
  MyList: TMyList;
  MyThread: TMyThread;

implementation

{$R *.dfm}

procedure TForm1.Button2Click(Sender: TObject);
begin
  if assigned(MyThread) then
  begin
    MyThread.Terminate; // Setzt MyThread nicht auf NIL, d.h. nächster Button2Click führt wieder in diesn Block
    Button2.Caption := 'Start Thread';
  end
  else
  begin
    Button2.Caption := 'Terminate Thread';
    MyThread := TMyThread.Create(true); // Create suspended--secondProcess does not run yet.
    MyThread.FreeOnTerminate := true; // You do not need to clean up after termination.
    MyThread.SleepTime := SpinEdit1.Value;
    MyThread.Resume; // Now run the thread.
  end;
end;

procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  MyList.Free;
  MyThread.Terminate;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  MyList := TMyList.Create;
end;

procedure TForm1.SpinEdit1Change(Sender: TObject);
begin
  if assigned(MyThread) then
    MyThread.SleepTime := SpinEdit1.Value;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  i: Integer;
begin
  for i := 0 to 20 do
    MyList.Add(random(200));
end;

{ TMyThread }

procedure TMyThread.Execute;
var
  i: Integer;
begin
  inherited;

  while (true) do
  begin
    if Terminated then
      exit;

    inc(FCounter);
    Form1.Label1.Caption := IntToStr(FCounter);
    Form1.Memo1.Clear;

    System.TMonitor.Enter(MyList); // Liste gegen Zweitzugriff sperren. Muss das sein?
    try
      for i := 0 to MyList.Count - 1 do
      begin
        if Terminated then
          exit;
        Form1.Memo1.Lines.Add(format('%d: %d', [i, MyList.Items[i]])); // Ist das zulässig?
      end;
    finally
      System.TMonitor.exit(MyList); // Sperrung der Liste wieder aufheben
    end;
    sleep(FSleepTime); // FSleepTime oder besser SleepTime?
  end;
end;

end.