关于Synchronize(50分)

有这个程序，是关于线程的：
unit MainForm;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
StdCtrls, ExtCtrls, Paintth;
type
TForm1 = class(TForm)
Button1: TButton;
Button2: TButton;
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
procedure FormMouseDown(Sender: TObject;
Button: TMouseButton;
Shift: TShiftState;
X, Y: Integer);
private
{ Private declarations }
PT: TPainterThread;
public
{ Public declarations }
end;

var
Form1: TForm1;
implementation
{$R *.DFM}
procedure TForm1.Button1Click(Sender: TObject);
begin
Button1.Enabled := False;
Button2.Enabled := True;
PT := TPainterThread.Create (False);
// start
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
PT.Free;
Button1.Enabled := True;
Button2.Enabled := False;
end;

procedure TForm1.FormMouseDown(Sender: TObject;
Button: TMouseButton;
Shift: TShiftState;
X, Y: Integer);
begin
Canvas.Pen.Color := Color;
// of the form
Canvas.Brush.Color := Color;
Canvas.Ellipse (x - 30, y - 30, x + 30, y + 30);
end;

end.


unit paintth;
interface
uses
Classes;
type
TPainterThread = class(TThread)
private
X, Y: Integer;
protected
procedure Execute;
override;
procedure Paint;
end;

implementation
{ TPainterThread }
uses
MainForm, Graphics;
procedure TPainterThread.Paint;
begin
Form1.Canvas.Pixels [X, Y] := clRed;
end;

procedure TPainterThread.Execute;
begin
Randomize;
repeat
X := Random (300);
Y := Random (Form1.ClientHeight);
Synchronize (Paint);
until Terminated;
end;

end.
我想问，unit MainForm;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
StdCtrls, ExtCtrls, Paintth;
type
TForm1 = class(TForm)
Button1: TButton;
Button2: TButton;
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
procedure FormMouseDown(Sender: TObject;
Button: TMouseButton;
Shift: TShiftState;
X, Y: Integer);
private
{ Private declarations }
PT: TPainterThread;
public
{ Public declarations }
end;

var
Form1: TForm1;
implementation
{$R *.DFM}
procedure TForm1.Button1Click(Sender: TObject);
begin
Button1.Enabled := False;
Button2.Enabled := True;
PT := TPainterThread.Create (False);
// start
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
PT.Free;
Button1.Enabled := True;
Button2.Enabled := False;
end;

procedure TForm1.FormMouseDown(Sender: TObject;
Button: TMouseButton;
Shift: TShiftState;
X, Y: Integer);
begin
Canvas.Pen.Color := Color;
// of the form
Canvas.Brush.Color := Color;
Canvas.Ellipse (x - 30, y - 30, x + 30, y + 30);
end;

end.


unit paintth;
interface
uses
Classes;
type
TPainterThread = class(TThread)
private
X, Y: Integer;
protected
procedure Execute;
override;
procedure Paint;
end;

implementation
{ TPainterThread }
uses
MainForm, Graphics;
procedure TPainterThread.Paint;
begin
Form1.Canvas.Pixels [X, Y] := clRed;
end;

procedure TPainterThread.Execute;
begin
Randomize;
repeat
X := Random (300);
Y := Random (Form1.ClientHeight);
Synchronize (Paint);
until Terminated;
end;

end.
unit MainForm;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
StdCtrls, ExtCtrls, Paintth;
type
TForm1 = class(TForm)
Button1: TButton;
Button2: TButton;
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
procedure FormMouseDown(Sender: TObject;
Button: TMouseButton;
Shift: TShiftState;
X, Y: Integer);
private
{ Private declarations }
PT: TPainterThread;
public
{ Public declarations }
end;

var
Form1: TForm1;
implementation
{$R *.DFM}
procedure TForm1.Button1Click(Sender: TObject);
begin
Button1.Enabled := False;
Button2.Enabled := True;
PT := TPainterThread.Create (False);
// start
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
PT.Free;
Button1.Enabled := True;
Button2.Enabled := False;
end;

procedure TForm1.FormMouseDown(Sender: TObject;
Button: TMouseButton;
Shift: TShiftState;
X, Y: Integer);
begin
Canvas.Pen.Color := Color;
// of the form
Canvas.Brush.Color := Color;
Canvas.Ellipse (x - 30, y - 30, x + 30, y + 30);
end;

end.


unit paintth;
interface
uses
Classes;
type
TPainterThread = class(TThread)
private
X, Y: Integer;
protected
procedure Execute;
override;
procedure Paint;
end;

implementation
{ TPainterThread }
uses
MainForm, Graphics;
procedure TPainterThread.Paint;
begin
Form1.Canvas.Pixels [X, Y] := clRed;
end;

procedure TPainterThread.Execute;
begin
Randomize;
repeat
X := Random (300);
Y := Random (Form1.ClientHeight);
Synchronize (Paint);
until Terminated;
end;

end.
我想问：Synchronize 有啥用？我去掉它程序一样可运行。
还有，怎样知一个线程是主线程？
请高手们详细点，我对线程还是初鸟！！！！！

Synchronize可以让线程的一些方法在主线程中执行.

各位大虾能按着程序说说吗？

《delphi5开发人员指南》中有详细解答

Synchronize 方法主要是用于同步 VCL 的代码，因为 VCL 不是线程安全的，使用 Synchronize
可以解决 VCL 的并发冲突，由于并发冲突发生的几率很小，所以你去掉它暂时不会发现问题。

能说说啥是同步 VCL 吗？

>>

还有，我想问问什么是线程安全，什么是线程重入？
谢谢了！！！

虽然答应你把这个问题回答了，但泛泛的解释对你是不够的
同意：caizongjie523
《delphi5开发人员指南》中有详细解答
郭玉梁和BaKuBaKu的解释也是对的，希望你翻一下书

那《delphi5开发人员指南》在那有的买？
我那没得买。。。

delphi5开发人员指南 138元
www.dangdang.com 有卖，我那时是五折买的，送货上门，不知道现在多少钱了。
如果你在教育网，可以到这里下载电子版，要不就免了。
ftp://ftp.xjtu.edu.cn/pub/document/china-pub/chinapub_unix_programming/Programming/Delphi 5开发人员指南

to wjiachun
能說說它的具體内容嗎？

我买了！