delphi 多线程之 TEvent 和 TLightweightEvent

Posted 2020-10-06 jjw

unit Unit1;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls,  system.SyncObjs;

type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    Memo1: TMemo;
    CheckBox1: TCheckBox;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure CheckBox1Click(Sender: TObject);
  private
  public
    { Public declarations }
  end;

  TMyThread = class(TThread)
  protected
    procedure Execute; override;
  end;

var
  Form1: TForm1;
  AEvent: TEvent;
  MyThread: TMyThread;

implementation

{$R *.dfm}

procedure Log(Msg: string);
begin
  TThread.Synchronize(nil, procedure begin
    Form1.Memo1.Lines.Add(Msg);
  end);
end;

{ TMyThread }

procedure TMyThread.Execute;
begin
  while not Terminated do
  begin
    AEvent.Acquire;
    Log(DateTimeToStr(Now));
    TThread.Sleep(500);
  end;
  Log(‘Exit‘);
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  AEvent.SetEvent;
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  AEvent.ResetEvent;
end;

procedure TForm1.CheckBox1Click(Sender: TObject);
begin
  MyThread.Terminate;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  Memo1.Clear;
  AEvent := TEvent.Create(nil, False, False, ‘‘);
  MyThread := TMyThread.Create(False);
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  if not MyThread.Finished then
  begin
    //确保线程正常退出
    MyThread.Terminate;
    AEvent.SetEvent;
    MyThread.WaitFor;
  end;
  MyThread.Free;

  AEvent.Free;
end;

end.

 

AEvent := TEvent.Create(nil, False, False, ‘‘);

第一个False, 线程是否可以执行一次. 如何为True,相当于 do  while, 如果为 False , 相当于 while .
第二个False, 相当于线程是否可以直接运行，不需要SetEvent. 如果为 True , 则必须调用 SetEvent 后，线程才能运行。也就是线程启动后就被阻塞住。
当两个同时为 False 时， 就可以实现类似 PulseOneEvent 的功能。



TLightweightEvent 和 TEvent 基本上是一样的，它是从 .NET中的 System.Threading.ManualResetEventSlim 学来的。对于多核，短时间间隔效率更好，可参考 MSDN 。