多线程编程(10) - 多线程同步之 Mutex (互斥对象)
2021/4/30 12:55:11
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多线程编程(10) - 多线程同步之 Mutex (互斥对象)
原理分析:
互斥对象是系统内核对象, 各线程都可以拥有它, 谁拥有谁就能执行;
执行完毕, 用 ReleaseMutex 函数释放拥有权, 以让其他等待的线程使用.
其他线程可用 WaitForSingleObject 函数排队等候(等候也可以理解为排队申请).
使用过程:
var hMutex: THandle; {应该先声明一个全局的互斥句柄} CreateMutex {建立一个互斥对象} WaitForSingleObject {用等待函数排队等候} ReleaseMutex {释放拥有权} CloseHandle {最后释放互斥对象}
ReleaseMutex、CloseHandle 的参数都是 CreateMutex 返回的句柄, 关键是 CreateMutex 函数:
function CreateMutex( lpMutexAttributes: PSecurityAttributes; bInitialOwner: BOOL; {是否让创建者(此例中是主线程)拥有该互斥对象} lpName: PWideChar {可以给此互斥对象取个名字, 如果不要名字可赋值为 nil} ): THandle; { 1、第一个参数前面说过. 2、第二个参数在这里一定要是 False, 如果让主线程拥有互斥, 从理论上讲, 得等程序退出后其他线程才有机会; 取值 False 时, 第一个执行的线程将会最先拥有互斥对象, 一旦拥有其他线程就得先等等. 3、第三个参数, 如果给个名字, 函数将从系统中寻找是否有重名的互斥对象, 如果有则返回同名对象的存在的句柄; 如果赋值为 nil 将直接创建一个新的互斥对象; 下个例子将会有名字. }
本例效果图:
代码文件:
unit Unit1; interface uses Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls; type TForm1 = class(TForm) Button1: TButton; procedure Button1Click(Sender: TObject); procedure FormCreate(Sender: TObject); procedure FormDestroy(Sender: TObject); end; var Form1: TForm1; implementation {$R *.dfm} var f: Integer; {用这个变量协调一下各线程输出的位置} hMutex: THandle; {互斥对象的句柄} function MyThreadFun(p: Pointer): DWORD; stdcall; var i,y: Integer; begin Inc(f); y := 20 * f; for i := 0 to 50000 do begin if WaitForSingleObject(hMutex, INFINITE) = WAIT_OBJECT_0 then begin Form1.Canvas.Lock; Form1.Canvas.TextOut(20, y, IntToStr(i)); Form1.Canvas.Unlock; Sleep(0); {稍稍耽搁一点, 不然有时 Canvas 会协调不过来} ReleaseMutex(hMutex); end; end; Result := 0; end; procedure TForm1.Button1Click(Sender: TObject); var ThreadID: DWORD; begin Repaint; f := 0; CreateThread(nil, 0, @MyThreadFun, nil, 0, ThreadID); CreateThread(nil, 0, @MyThreadFun, nil, 0, ThreadID); CreateThread(nil, 0, @MyThreadFun, nil, 0, ThreadID); CreateThread(nil, 0, @MyThreadFun, nil, 0, ThreadID); CreateThread(nil, 0, @MyThreadFun, nil, 0, ThreadID); end; procedure TForm1.FormCreate(Sender: TObject); begin hMutex := CreateMutex(nil, False, nil); end; procedure TForm1.FormDestroy(Sender: TObject); begin CloseHandle(hMutex); end; end.
窗体文件:
object Form1: TForm1 Left = 0 Top = 0 Caption = 'Form1' ClientHeight = 140 ClientWidth = 192 Color = clBtnFace Font.Charset = DEFAULT_CHARSET Font.Color = clWindowText Font.Height = -11 Font.Name = 'Tahoma' Font.Style = [] OldCreateOrder = False OnCreate = FormCreate PixelsPerInch = 96 TextHeight = 13 object Button1: TButton Left = 109 Top = 107 Width = 75 Height = 25 Caption = 'Button1' TabOrder = 0 OnClick = Button1Click end end
SyncObjs 单元下有封装好的 TMutex 类, 好像不如 Api 快, 内部机制也稍有区别, 但使用方法差不多:
unit Unit1; interface uses Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls; type TForm1 = class(TForm) Button1: TButton; procedure Button1Click(Sender: TObject); procedure FormCreate(Sender: TObject); procedure FormDestroy(Sender: TObject); end; var Form1: TForm1; implementation {$R *.dfm} uses SyncObjs; var f: Integer; MyMutex: TMutex; function MyThreadFun(p: Pointer): DWORD; stdcall; var i,y: Integer; begin Inc(f); y := 20 * f; for i := 0 to 50000 do begin if MyMutex.WaitFor(INFINITE) = wrSignaled then begin Form1.Canvas.Lock; Form1.Canvas.TextOut(20, y, IntToStr(i)); Form1.Canvas.Unlock; MyMutex.Release; end; end; Result := 0; end; procedure TForm1.Button1Click(Sender: TObject); var ThreadID: DWORD; begin Repaint; f := 0; CreateThread(nil, 0, @MyThreadFun, nil, 0, ThreadID); CreateThread(nil, 0, @MyThreadFun, nil, 0, ThreadID); CreateThread(nil, 0, @MyThreadFun, nil, 0, ThreadID); CreateThread(nil, 0, @MyThreadFun, nil, 0, ThreadID); CreateThread(nil, 0, @MyThreadFun, nil, 0, ThreadID); end; procedure TForm1.FormCreate(Sender: TObject); begin MyMutex := TMutex.Create(False); end; procedure TForm1.FormDestroy(Sender: TObject); begin MyMutex.Free; end; end.posted on 2009-02-13 21:25 万一 阅读(12738) 评论(32) 编辑 收藏
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