三天不写代码就手生！ 把测试代码记录下来。

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)
    Button1: TButton;
    Button2: TButton;
    Button3: TButton;
    Button4: TButton;
    Memo1: TMemo;
    CheckBox1: TCheckBox;
    CheckBox2: TCheckBox;
    procedure FormCreate(Sender: TObject);
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  private
    FFlag: Boolean;
  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
  //错误
  if  System.MonitorTryEnter(Form1) then
  begin
    System.MonitorEnter(Form1);
    System.MonitorPulseAll(Form1);
    System.MonitorExit(Form1);
  end
  else
    Log('????');
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  //正确
  System.MonitorPulseAll(Form1);
end;

procedure TForm1.FormCreate(Sender: TObject);
var
  AThread: TThread;
begin
  FFlag := True;
  TThread.CreateAnonymousThread(procedure
    begin
      while True do
      begin
        if Form1.CheckBox2.Checked then
          Exit;

        if Form1.FFlag then
        begin
            System.MonitorEnter(Form1);  //必须
            Log('Thread1 Enter');
            System.MonitorWait(Form1, INFINITE);
            Log('Thread1 WaitFor');
            System.MonitorExit(Form1);   //必须
            Log('Thread1 Exit');
        end;

        Log(DateTimeToStr(Now));
        TThread.Sleep(100);
      end;
      Log('Thread Exit');
    end).Start;

  TThread.CreateAnonymousThread(procedure
    begin
      while True do
      begin
        if Form1.CheckBox2.Checked then
          Exit;

        if Form1.FFlag then
        begin
            System.MonitorEnter(Form1);
            Log('Thread2 Enter');
            System.MonitorWait(Form1, INFINITE);
            Log('Thread2 WaitFor');
            System.MonitorExit(Form1);
            Log('Thread2 Exit');
        end;

        Log(DateTimeToStr(Now));
        TThread.Sleep(100);
      end;
      Log('Thread Exit');
    end).Start;
end;

end.

注意事项：

1. 三个方法必须一块使用，不能只写 System.MonitorWait(Form1, INFINITE);

            System.MonitorEnter(Form1);  //必须
            Log('Thread1 Enter');
            System.MonitorWait(Form1, INFINITE);
            Log('Thread1 WaitFor');
            System.MonitorExit(Form1);   //必须
            Log('Thread1 Exit');

2.  System.MonitorPulseAll(Form1) 即可。不要这样写

    System.MonitorEnter(Form1);
    System.MonitorPulseAll(Form1);
    System.MonitorExit(Form1);