TNewThread = class(TThread)
  private
    { Private declarations }
  protected
    procedure Execute; override;
  end;


var
  Form1: TForm1;

implementation

{$R *.dfm}

{ TNewThread }

procedure TNewThread.Execute;
begin
  while true do {ничего не делаем};
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  NewThread: TNewThread;
begin
  NewThread:=TNewThread.Create(true);
  NewThread.FreeOnTerminate:=true;
  NewThread.Priority:=tpLower;
  NewThread.Resume;
end;

NewThread:=TNewThread.Create(true); 

New.FreeOnTerminate := true; 

NewThread.Priority:=tpLower; 

• tpTimeCritical - критический
• tpHighest - очень высокий
• tpHigher - высокий
• tpNormal - средний
• tpLower - низкий
• tpLowest - очень низкий
• tpIdle - поток работает во время простоя системы

NewThread.Resume; 

Синхронизации потоков

TNewThread = class(TThread)
  private
    Progress: integer;
    procedure SetProgress;
  protected
    procedure Execute; override;
  end;
...

procedure TNewThread.Execute;
var
  i: integer;
begin
  for i:=0 to 100 do
  begin
    sleep(50);
    Progress:=i;
    Synchronize(SetProgress);
  end;
end;

procedure TNewThread.SetProgress;
begin
  Form1.ProgressBar1.Position:=Progress;
end;

const
  PROGRESS_POS = WM_USER+1;

  TForm1 = class(TForm)
    Button1: TButton;
    ProgressBar1: TProgressBar;
    procedure Button1Click(Sender: TObject);
  private
    procedure SetProgressPos(var Msg: TMessage); message PROGRESS_POS;
  public
    { Public declarations }
  end;
...

procedure TForm1.SetProgressPos(var Msg: TMessage);
begin
  ProgressBar1.Position:=Msg.LParam;
end;

procedure TNewThread.Execute;
var
  i: integer;
begin
  for i:=0 to 100 do
  begin
    sleep(50);
    SendMessage(Form1.Handle,PROGRESS_POS,0,i);
  end;
end;

Критические секции

var
  Form1: TForm1;
  CriticalSection: TCriticalSection;

...

procedure TForm1.FormCreate(Sender: TObject);
begin
  CriticalSection:=TCriticalSection.Create;
end;

procedure TNewThread.Execute;
var
  i: integer;
begin
  CriticalSection.Enter;
  for i:=0 to 100 do
  begin
    sleep(50);
    SendMessage(Form1.Handle,PROGRESS_POS,0,i);
  end;
  CriticalSection.Leave;
end;