多线程编程(3) - 从 CreateThread 说起[续]
function CreateThread( lpThreadAttributes: Pointer; dwStackSize: DWORD; lpStartAddress: TFNThreadStartRoutine; lpParameter: Pointer; dwCreationFlags: DWORD; {启动选项} var lpThreadId: DWORD ): THandle; stdcall;
CreateThread 的倒数第二个参数 dwCreationFlags(启动选项) 有两个可选值:
0: 线程建立后立即执行入口函数;
CREATE_SUSPENDED: 线程建立后会挂起等待.
可用 ResumeThread 函数是恢复线程的运行; 可用 SuspendThread 再次挂起线程.
这两个函数的参数都是线程句柄, 返回值是执行前的挂起计数.
什么是挂起计数?
SuspendThread 会给这个数 +1; ResumeThread 会给这个数 -1; 但这个数最小是 0.
当这个数 = 0 时, 线程会运行; > 0 时会挂起.
如果被 SuspendThread 多次, 同样需要 ResumeThread 多次才能恢复线程的运行.
在下面的例子中, 有新线程不断给一个全局变量赋随机值;
同时窗体上的 Timer 控件每隔 1/10 秒就把这个变量写在窗体标题;
在这个过程中演示了 ResumeThread、SuspendThread 两个函数.
运行效果图:
代码文件:
unit Unit1; interface uses Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls, ExtCtrls; type TForm1 = class(TForm) Button1: TButton; Button2: TButton; Button3: TButton; Timer1: TTimer; procedure Button1Click(Sender: TObject); procedure Button2Click(Sender: TObject); procedure Button3Click(Sender: TObject); procedure FormCreate(Sender: TObject); procedure Timer1Timer(Sender: TObject); end; var Form1: TForm1; implementation {$R *.dfm} var hThread: THandle; {线程句柄} num: Integer; {全局变量, 用于记录随机数} {线程入口函数} function MyThreadFun(p: Pointer): Integer; stdcall; begin while True do {假如线程不挂起, 这个循环将一直循环下去} begin num := Random(100); end; Result := 0; end; {建立并挂起线程} procedure TForm1.Button1Click(Sender: TObject); var ID: DWORD; begin hThread := CreateThread(nil, 0, @MyThreadFun, nil, CREATE_SUSPENDED, ID); Button1.Enabled := False; end; {唤醒并继续线程} procedure TForm1.Button2Click(Sender: TObject); begin ResumeThread(hThread); end; {挂起线程} procedure TForm1.Button3Click(Sender: TObject); begin SuspendThread(hThread); end; {下面是窗体代码} procedure TForm1.FormCreate(Sender: TObject); begin Timer1.Interval := 100; end; procedure TForm1.Timer1Timer(Sender: TObject); begin Text := IntToStr(num); end; end.
窗体文件:
object Form1: TForm1 Left = 0 Top = 0 Caption = 'Form1' ClientHeight = 86 ClientWidth = 269 Color = clBtnFace Font.Charset = DEFAULT_CHARSET Font.Color = clWindowText Font.Height = -11 Font.Name = 'Tahoma' Font.Style = [] OldCreateOrder = False OnCreate = FormCreate PixelsPerInch = 96 TextHeight = 13 object Button1: TButton Left = 16 Top = 24 Width = 75 Height = 25 Caption = 'Button1' TabOrder = 0 OnClick = Button1Click end object Button2: TButton Left = 97 Top = 24 Width = 75 Height = 25 Caption = 'Button2' TabOrder = 1 OnClick = Button2Click end object Button3: TButton Left = 178 Top = 24 Width = 75 Height = 25 Caption = 'Button3' TabOrder = 2 OnClick = Button3Click end object Timer1: TTimer OnTimer = Timer1Timer end end
ResumeThread 和 SuspendThread 分别对应 TThread 的 Resume 和 Suspend 方法, 很好理解.
接下来应该是 CreateThread 的第四个参数了.
posted on 2009-02-10 17:48 万一 阅读(19793) 评论(31) 编辑 收藏