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多線程編程(3) - 從 CreateThread 說起[續(xù)]。                                                            
                        
function CreateThread(
　lpThreadAttributes: Pointer;
　dwStackSize: DWORD;
　lpStartAddress: TFNThreadStartRoutine;
　lpParameter: Pointer;
　dwCreationFlags: DWORD; {啟動(dòng)選項(xiàng)}
　var lpThreadId: DWORD
): THandle; stdcall;
　　CreateThread 的倒數(shù)第二個(gè)參數(shù) dwCreationFlags(啟動(dòng)選項(xiàng)) 有兩個(gè)可選值:
　　0: 線程建立后立即執(zhí)行入口函數(shù);
　　CREATE_SUSPENDED: 線程建立后會(huì)掛起等待.
　　可用 ResumeThread 函數(shù)是恢復(fù)線程的運(yùn)行; 可用 SuspendThread 再次掛起線程.
　　這兩個(gè)函數(shù)的參數(shù)都是線程句柄, 返回值是執(zhí)行前的掛起計(jì)數(shù).
　　什么是掛起計(jì)數(shù)?
　　SuspendThread 會(huì)給這個(gè)數(shù) +1; ResumeThread 會(huì)給這個(gè)數(shù) -1; 但這個(gè)數(shù)最小是 0.
　　當(dāng)這個(gè)數(shù) = 0 時(shí), 線程會(huì)運(yùn)行; > 0 時(shí)會(huì)掛起.
　　如果被 SuspendThread 多次, 同樣需要 ResumeThread 多次才能恢復(fù)線程的運(yùn)行.
　　在下面的例子中, 有新線程不斷給一個(gè)全局變量賦隨機(jī)值;
　　同時(shí)窗體上的 Timer 控件每隔 1/10 秒就把這個(gè)變量寫在窗體標(biāo)題;
　　在這個(gè)過程中演示了 ResumeThread、SuspendThread 兩個(gè)函數(shù).
　　運(yùn)行效果圖:

　　

　代碼文件: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; {線程句柄}
　num: Integer;　　 {全局變量, 用于記錄隨機(jī)數(shù)}
{線程入口函數(shù)}
function MyThreadFun(p: Pointer): Integer; stdcall;
begin
　while True do {假如線程不掛起, 這個(gè)循環(huán)將一直循環(huán)下去}
　begin
　　num := Random(100);
　end;
　Result := 0;
end;
{建立并掛起線程}
procedure TForm1.Button1Click(Sender: TObject);
var
　ID: DWORD;
begin
　hThread := CreateThread(nil, 0, @MyThreadFun, nil, CREATE_SUSPENDED, ID);
　Button1.Enabled := False;
end;
{喚醒并繼續(xù)線程}
procedure TForm1.Button2Click(Sender: TObject);
begin
　ResumeThread(hThread);
end;
{掛起線程}
procedure TForm1.Button3Click(Sender: TObject);
begin
　SuspendThread(hThread);
end;
{下面是窗體代碼}
procedure TForm1.FormCreate(Sender: TObject);
begin
　Timer1.Interval := 100;
end;
procedure TForm1.Timer1Timer(Sender: TObject);
begin
　Text := IntToStr(num);
end;
end.

　窗體文件: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 分別對(duì)應(yīng) TThread 的 Resume 和 Suspend 方法, 很好理解.

　　接下來應(yīng)該是 CreateThread 的第四個(gè)參數(shù)了.