多线程编程(19) 不使用同步工具, 手动协调线程依次执行

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.

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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

第一个例子的代码文件(窗体同上):

---

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;
  hMutex: THandle; {互斥对象的句柄}

function ThreadFun(p: Pointer): Integer; stdcall;
var
  i,n,x1,y1,x2,y2: Integer;
begin
  n := Integer(p);
  panitArr[n].Color := colors[n];

  if WaitForSingleObject(hMutex, INFINITE) = WAIT_OBJECT_0 then
  begin
    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(10);
    end;
    ReleaseMutex(hMutex);
  end;
  Result := 0;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  ID: DWORD;
  i: Integer;
begin
  panitArr[0] := PaintBox1;
  panitArr[1] := PaintBox2;
  panitArr[2] := PaintBox3;

  CloseHandle(hMutex);
  hMutex := CreateMutex(nil, False, nil);
  for i := 0 to Length(hArr) - 1 do
    hArr[i] := CreateThread(nil, 0, @ThreadFun, Ptr(i), 0, ID);
end;

procedure TForm1.FormDestroy(Sender: TObject);
var
  i: Integer;
begin
  CloseHandle(hMutex);
  for i := 0 to Length(hArr) - 1 do CloseHandle(hArr[i]);
end;

end.