unit Unit1;

interface

uses

  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,

  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;

type

  TForm1 = class(TForm)

    CheckBox1: TCheckBox;

    CheckBox2: TCheckBox;

    Button1: TButton;

    Button2: TButton;

    Memo1: TMemo;

    procedure FormCreate(Sender: TObject);

    procedure Button1Click(Sender: TObject);

    procedure Button2Click(Sender: TObject);

  private

    { Private declarations }

  public

    { Public declarations }

  end;

var

  Form1: TForm1;

implementation

{$R *.dfm}

procedure Log(Msg: string);

begin

  TThread.Synchronize(nil, procedure

    begin

      Form1.Memo1.Lines.Add(Msg);

    end);

end;

procedure TForm1.Button1Click(Sender: TObject);

begin

  if System.MonitorTryEnter(Self) then  //如果为 True

  begin

    Color := clRed;

    System.MonitorExit(Self);    //也必须退出，否则 System.MonitorPulse(Self); 失效。

  end;

end;

procedure TForm1.Button2Click(Sender: TObject);

begin

  System.MonitorPulse(Self);

end;

procedure TForm1.FormCreate(Sender: TObject);

begin

  TThread.CreateAnonymousThread(procedure

    begin

      while True do

      begin

        if Form1.CheckBox2.Checked then

          Exit;

        System.MonitorEnter(Form1);  //必须

        Log('Thread1 Enter');

        System.MonitorWait(Form1, INFINITE);

        Log('Thread1 WaitFor');

        System.MonitorExit(Form1);   //必须

        Log('Thread1 Exit');

        Log(DateTimeToStr(Now));

        TThread.Sleep();

      end;

      Log('Thread Exit');

    end).Start;

end;

end.

注意事项：
  if System.MonitorTryEnter(Self) then  //如果为 True
  begin
    Color := clRed;
    System.MonitorExit(Self);    //也必须退出（释放），否则 System.MonitorPulse(Self); 失效。
  end;

System.MonitorTryEnter 与 System.MonitorEnter 的区别在于是否会 block 当前调用 System.MonitorEnter 或 System.MonitorTryEnter 的线程。

System.MonitorEnter 会 block 调用线程
System.MonitorTryEnter 不会 block 调用线程。

此外

        System.MonitorEnter(Form1);

        System.MonitorWait(Form1, INFINITE);  //执行后, Button1的onclick事件中，System.MonitorTryEnter(Self) 总会返回 True