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(100);
      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