关于多线程同步向Memo1中写数据的有关问题（）

关于多线程同步向Memo1中写数据的问题（高手请进）
以下代码
unit   Unit1;

interface

uses
    Windows,   Messages,   SysUtils,   Variants,   Classes,   Graphics,   Controls,   Forms,
    Dialogs,   StdCtrls,   Buttons;

type

    TMainThread   =   class(TThread)
    private
        FCount:   LongInt;
        procedure   WriteFcout;
    public
        procedure   Execute;   override;
        constructor   Create(IsSuspend:   Boolean);
    end;
    TCenterThread   =   class(TThread)
    private
        FCount:   LongInt;
        procedure   WriteFcout;
    public
        procedure   Execute;   override;
        constructor   Create(IsSuspend:   Boolean);
    end;
    TForm1   =   class(TForm)
        Button1:   TButton;
        Memo1:   TMemo;
        procedure   Button1Click(Sender:   TObject);
        procedure   FormDestroy(Sender:   TObject);
        procedure   FormShow(Sender:   TObject);
    private
        {   Private   declarations   }
        FP:   TStringList;
    public
        {   Public   declarations   }

    end;

var
    Form1:   TForm1;
    ThreadLock:   LongInt;
    MainThread:   TMainThread;
    CenterThread:   TCenterThread;
implementation

{$R   *.dfm}

constructor   TMainThread.Create(IsSuspend:   Boolean);
begin
    inherited   Create(IsSuspend);
    FreeOnTerminate   :=   True;
    FCount   :=   0;
end;

procedure   TMainThread.Execute;
var   i:   Integer;
begin
    i   :=   0;
    while   i   <   10   do
    begin
        Inc(FCount);
        Synchronize(WriteFcout);        
        InterlockedIncrement(ThreadLock);
        if   CenterThread.Suspended   then
            CenterThread.Resume;
        Inc(i);
    end;
end;

procedure   TMainThread.WriteFcout;
begin
    Form1.Memo1.Lines.Add( 'A ');
end;

constructor   TCenterThread.Create(IsSuspend:   Boolean);
begin
    inherited   Create(IsSuspend);
    FreeOnTerminate   :=   True;
    FCount   :=   0;
end;

procedure   TCenterThread.Execute;
var   i:   LongInt;
begin
    while   not   Terminated   do
    begin
        if   ThreadLock   >   0   then
        begin