多线程编程（19） - 不使用同步工具,手动协调线程依次执行

多线程编程（19） - 不使用同步工具,手动协调线程依次执行2009-12-10 博客园万一在前面例子的基础上, 探讨新问题.

假如我们想让几个线程（例子中是 3 个）依次执行, 我们可以使用临界区、信号、互斥等手段;

但下面第一个例子什么同步工具都没用, 也达到了目的; 方法是: 让前一个线程在结束前顺便启动下一个线程.

第二个例子使用了互斥对象配合 WaitForSingleObject 函数, 也达到相似的目的.

效果图（两个例子的效果图差不多, 但第二个例子的执行顺序不好保证）:

第一个例子的代码文件:

unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls, ExtCtrls;
type
TForm1 = class（TForm）
PaintBox1: TPaintBox;
PaintBox2: TPaintBox;
PaintBox3: TPaintBox;
Button1: TButton;
procedure Button1Click（Sender: TObject）;
procedure FormDestroy（Sender: TObject）;
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
const
colors: array[0..2] of TColor = （clRed, clGreen, clBlue）;
var
hArr: array[0..2] of THandle;
panitArr: array[0..2] of TPaintBox;
function ThreadFun（p: Pointer）: Integer; stdcall;
var
i,n,x1,y1,x2,y2: Integer;
ThreadID: DWORD;
begin
n := Integer（p）;
panitArr[n].Color := colors[n];
for i := 0 to 50 do with panitArr[n] do
begin
x1 := Random（Width）; y1 := Random（Height）;
x2 := Random（Width）; y2 := Random（Height）;
Canvas.Lock;
Canvas.Ellipse（x1,y1,x2,y2）;
Canvas.Unlock;
Sleep（2）;
end;
{在前一个线程收尾时, 如果新建线程不超过 3 个就继续建立}
Inc（n）;
if n < 3 then hArr[n] := CreateThread（nil, 0, @ThreadFun, Ptr（n）, 0, ThreadID）;
Result := 0;
end;
procedure TForm1.Button1Click（Sender: TObject）;
var
ID: DWORD;
begin
panitArr[0] := PaintBox1;
panitArr[1] := PaintBox2;
panitArr[2] := PaintBox3;
{开始只建立了一个线程, 并传入 0 参数作为标识}
hArr[0] := CreateThread（nil, 0, @ThreadFun, Ptr（0）, 0, ID）;
end;
procedure TForm1.FormDestroy（Sender: TObject）;
var
i: Integer;
begin
for i := 0 to Length（hArr） - 1 do CloseHandle（hArr[i]）;
end;
end.

窗体文件:

object Form1: TForm1
Left = 0
Top = 0
Caption = "Form1"
ClientHeight = 156
ClientWidth = 321
Color = clBtnFace
Font.Charset = DEFAULT_CHARSET
Font.Color = clWindowText
Font.Height = -11
Font.Name = "Tahoma"
Font.Style = []
OldCreateOrder = False
OnDestroy = FormDestroy
PixelsPerInch = 96
TextHeight = 13
object PaintBox1: TPaintBox
Left = 8
Top = 8
Width = 97
Height = 113
end
object PaintBox2: TPaintBox
Left = 111
Top = 8
Width = 98
Height = 113
end
object PaintBox3: TPaintBox
Left = 215
Top = 8
Width = 98
Height = 113
end
object Button1: TButton
Left = 238
Top = 126
Width = 75
Height = 25
Caption = "Button1"
TabOrder = 0
OnClick = Button1Click
end
end