请教：如何通过进程中的一个全局变量控制两个子线程互斥？谢谢！ ( 积分: 50 )

  • 主题发起人 主题发起人 chenshu_sc
  • 开始时间 开始时间
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chenshu_sc

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我的程序如下：
unit FormMain;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls;
type
th1 = class(TThread)
s : string;
FStatus : Integer;
FMemo : TMemo;
private
procedure w;
procedure showresult;
protected
procedure Execute ;
override;
public
constructor Create(Suspended:Boolean ;
Status : Integer ;
mem : TMemo);
end;

th2 = class(TThread)
s : string;
FStatus : Integer;
FMemo : TMemo;
private
procedure w;
procedure showresult;
protected
procedure Execute ;
override;
public
constructor Create(Suspended:Boolean ;
Status : Integer ;
mem : TMemo);
end;

TForm1 = class(TForm)
Memo1: TMemo;
Button1: TButton;
Button2: TButton;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
i : Integer;
t1 : th1;
t2 : th2;
end;

var
Form1: TForm1;
implementation
{$R *.dfm}
procedure th1.w;
begin
try
if FStatus = 1 then
begin
FStatus := 2;
sleep(1000);
s := 'TH1';
FStatus := 1;
end;
finally
end;
end;

procedure th1.showresult;
begin
FMemo.Lines.Add(s);
end;

procedure th1.Execute ;
begin
while not terminateddo
begin
w;
Synchronize(showresult);
end;
end;

constructor th1.Create(Suspended:Boolean ;
Status : Integer ;
mem : TMemo);
begin
inherited Create(Suspended);
FreeOnTerminate:=True;
FStatus := Status;
FMemo := mem;
end;

procedure th2.w;
begin
try
if FStatus = 1 then
begin
FStatus := 2;
sleep(300);
s := 'TH2';
FStatus := 1;
end;
finally
end;
end;

procedure th2.showresult;
begin
FMemo.Lines.Add(s);
end;

procedure th2.Execute ;
begin
while not terminateddo
begin
w;
Synchronize(showresult);
end;
end;

constructor th2.Create(Suspended:Boolean ;
Status : Integer ;
mem : TMemo);
begin
inherited create(suspended);
FreeOnTerminate:=True;
FStatus := Status;
FMemo := mem;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
i := 1;
t1 := th1.Create(false,i,memo1);
t2 := th2.Create(false,i,memo1);
end;

end.

很明显没有达到要求，但不知道该怎么改？请各位大大帮忙！
 
我的程序如下：
unit FormMain;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls;
type
th1 = class(TThread)
s : string;
FStatus : Integer;
FMemo : TMemo;
private
procedure w;
procedure showresult;
protected
procedure Execute ;
override;
public
constructor Create(Suspended:Boolean ;
Status : Integer ;
mem : TMemo);
end;

th2 = class(TThread)
s : string;
FStatus : Integer;
FMemo : TMemo;
private
procedure w;
procedure showresult;
protected
procedure Execute ;
override;
public
constructor Create(Suspended:Boolean ;
Status : Integer ;
mem : TMemo);
end;

TForm1 = class(TForm)
Memo1: TMemo;
Button1: TButton;
Button2: TButton;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
i : Integer;
t1 : th1;
t2 : th2;
end;

var
Form1: TForm1;
implementation
{$R *.dfm}
procedure th1.w;
begin
try
if FStatus = 1 then
begin
FStatus := 2;
sleep(1000);
s := 'TH1';
FStatus := 1;
end;
finally
end;
end;

procedure th1.showresult;
begin
FMemo.Lines.Add(s);
end;

procedure th1.Execute ;
begin
while not terminateddo
begin
w;
Synchronize(showresult);
end;
end;

constructor th1.Create(Suspended:Boolean ;
Status : Integer ;
mem : TMemo);
begin
inherited Create(Suspended);
FreeOnTerminate:=True;
FStatus := Status;
FMemo := mem;
end;

procedure th2.w;
begin
try
if FStatus = 1 then
begin
FStatus := 2;
sleep(300);
s := 'TH2';
FStatus := 1;
end;
finally
end;
end;

procedure th2.showresult;
begin
FMemo.Lines.Add(s);
end;

procedure th2.Execute ;
begin
while not terminateddo
begin
w;
Synchronize(showresult);
end;
end;

constructor th2.Create(Suspended:Boolean ;
Status : Integer ;
mem : TMemo);
begin
inherited create(suspended);
FreeOnTerminate:=True;
FStatus := Status;
FMemo := mem;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
i := 1;
t1 := th1.Create(false,i,memo1);
t2 := th2.Create(false,i,memo1);
end;

end.

很明显没有达到要求，但不知道该怎么改？请各位大大帮忙！
 
procedure th1.w;
begin
try
if FStatus = 1 then
begin
FStatus := 3;
sleep(1000);
s := 'TH1';
FStatus := 2;
end;
finally
end;
end;

procedure th2.w;
begin
try
if FStatus = 2 then
begin
FStatus := 3;
sleep(300);
s := 'TH2';
FStatus := 1;
end;
finally
end;
end;
 
TO：lollman
　这样改了之后，线程不SLEEP啊。。。
 
另外，我感觉我目前的问题就是，如何在线程中改变进程中的全局变量？
 
楼主的问题用全局变量来解决是不正确的，因为全局变量不是线程安全的。
正确的方法是利用操作系统提供的互斥机制，因为线程/进程是由操作系统来调度的
DELPHI提供了相应的VCL对象来提供这种机制，楼主可以看看 TCriticalSection。
 
TO：沙隆巴斯的主人
　　用TCriticalSection我也试过，但效果并不符合要求，因为感觉如果用TCriticalSection的话，t1/t2是分别等待对方运行完毕之后就运行，而不是根据FStatus的值来决定是否运行....
以下是我用TMultireadExclusiveWriteSynchronizer做的程序，还请多指教：
unit FormMain;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls, SyncObjs;
type
th1 = class(TThread)
s : string;
FStatus : Integer;
FMemo : TMemo;
// cs : TCriticalSection;
lj : TMultireadExclusiveWriteSynchronizer;
private
procedure w;
procedure showresult;
protected
procedure Execute ;
override;
public
constructor Create(Suspended:Boolean ;
Status : Integer ;
mem : TMemo);
end;

th2 = class(TThread)
s : string;
FStatus : Integer;
FMemo : TMemo;
// cs : TCriticalSection;
lj : TMultireadExclusiveWriteSynchronizer;
private
procedure w;
procedure showresult;
protected
procedure Execute ;
override;
public
constructor Create(Suspended:Boolean ;
Status : Integer ;
mem : TMemo);
end;

thPause = class(TThread)
s : String;
FStatus : Integer;
FMemo : TMemo;
// cs : TCriticalSection;
lj : TMultireadExclusiveWriteSynchronizer;
private
procedure w;
procedure showresult;
protected
procedure Execute ;
override;
public
constructor Create(Suspended:Boolean ;
Status : Integer ;
mem : TMemo);
end;

TForm1 = class(TForm)
Memo1: TMemo;
Button1: TButton;
Button2: TButton;
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
i : Integer;
t1 : th1;
t2 : th2;
tPause : thPause;
end;

var
Form1: TForm1;
implementation
{$R *.dfm}
procedure th1.w;
begin
lj.begin
Read;
try
if FStatus = 1 then
begin
lj.begin
Write;
try
FStatus := 2;
sleep(2000);
s := 'TH1';
FStatus := 1;
// sleep(1000);
finally
lj.EndWrite;
end;
end;
finally
lj.EndRead;
end;
{
lj.begin
Write;
// cs.Enter;
try
if FStatus = 1 then
begin
FStatus := 2;
sleep(500);
s := 'TH1';
FStatus := 1;
sleep(1000);
end;
finally
// FStatus := 1;
lj.EndRead;
lj.EndWrite;
// cs.Leave;
end;
}
end;

procedure th1.showresult;
begin
FMemo.Lines.Add(s);
end;

procedure th1.Execute ;
begin
while not terminateddo
begin
w;
Synchronize(showresult);
end;
end;

constructor th1.Create(Suspended:Boolean ;
Status : Integer ;
mem : TMemo);
begin
inherited Create(Suspended);
FreeOnTerminate:=True;
FStatus := Status;
FMemo := mem;
// cs := TCriticalSection.Create;
lj := TMultireadExclusiveWriteSynchronizer.Create;
end;

procedure th2.w;
begin
lj.begin
Read;
try
s := IntToStr(FStatus);
if FStatus = 1 then
begin
lj.begin
Write;
try
FStatus := 2;
sleep(500);
// s := 'TH2';
FStatus := 1;
// sleep(1000);
finally
lj.EndWrite;
end;
end
else
begin
s := 'Th2 can not run cause FStatus <> 1!';
end;
finally
lj.EndRead;
end;
{
lj.begin
Read;
lj.begin
Write;
// cs.Enter;
try
if FStatus = 1 then
begin
FStatus := 2;
sleep(1000);
s := 'TH2';
FStatus := 1;
sleep(200);
end;
finally
// FStatus := 1;
lj.EndRead;
lj.EndWrite;
// cs.Leave;
end;
}
end;

procedure th2.showresult;
begin
FMemo.Lines.Add(s);
end;

procedure th2.Execute ;
begin
while not terminateddo
begin
w;
Synchronize(showresult);
end;
end;

constructor th2.Create(Suspended:Boolean ;
Status : Integer ;
mem : TMemo);
begin
inherited Create(Suspended);
FreeOnTerminate:=True;
FStatus := Status;
FMemo := mem;
// cs := TCriticalSection.Create;
lj := TMultireadExclusiveWriteSynchronizer.Create;
end;

procedure thPause.w;
begin
lj.begin
Read;
lj.begin
Write;
// cs.Enter;
try
FStatus := 0;
s := 'Pause';
finally
lj.EndRead;
lj.EndWrite;
// cs.Leave;
end;
end;

procedure thPause.showresult;
begin
FMemo.Lines.Add(s);
end;

procedure thPause.Execute ;
begin
w;
Synchronize(showresult);
end;

constructor thPause.Create(Suspended:Boolean ;
Status : Integer ;
mem : TMemo);
begin
inherited Create(Suspended);
FreeOnTerminate:=True;
FStatus := Status;
FMemo := mem;
// cs := TCriticalSection.Create;
lj := TMultireadExclusiveWriteSynchronizer.Create;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
i := 1;
t1 := th1.Create(false,i,memo1);
t2 := th2.Create(false,i,memo1);
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
tPause := thPause.Create(false,i,memo1);
end;

end.
 
另外重新说明一下我的问题：
　　有两个线程t1、t2，一个全局变量status，当t1、t2运行的时候先判断status的值，如果为1的话继续，否则退出。在继续运行前status置为2，运行完毕后置为1。这样应该比较清楚了吧：）
　　
 
to chenshu_sc:
用TCriticalSection来保护你的status就可以了啊。
 
cs.Enter;
FStatus := 2;
cs.Leave;
这不就结了？
 
TO：沙隆巴斯的主人＆lichengbin
　　谢谢两位的帮助，但我的问题好象并没有得到解决，因为我主要是想当程序运行的时候，th2有可能显示TH2也有可能显示'Th2 can not run cause FStatus <> 1!'，而TCriticalSection是独占读写的，所以如果用TCriticalSection的话不太可能实现，只有改用TMultireadExclusiveWriteSynchronizer，因为它是共享读独占写。
　　不过我写的程序好象并没有实现这个效果，以下是我将精简后的程序，请各位大大继续帮忙哈：）
unit FormMain;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls, SyncObjs;
type
th1 = class(TThread)
s : string;
FStatus : Integer;
FMemo : TMemo;
lj : TMultireadExclusiveWriteSynchronizer;
private
procedure w;
procedure showresult;
protected
procedure Execute ;
override;
public
constructor Create(Suspended:Boolean ;
Status : Integer ;
mem : TMemo);
end;

th2 = class(TThread)
s : string;
FStatus : Integer;
FMemo : TMemo;
lj : TMultireadExclusiveWriteSynchronizer;
private
procedure w;
procedure showresult;
protected
procedure Execute ;
override;
public
constructor Create(Suspended:Boolean ;
Status : Integer ;
mem : TMemo);
end;

TForm1 = class(TForm)
Memo1: TMemo;
Button1: TButton;
Button2: TButton;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
i : Integer;
t1 : th1;
t2 : th2;
end;

var
Form1: TForm1;
implementation
{$R *.dfm}
procedure th1.w;
begin
lj.begin
Read;
try
if FStatus = 1 then
begin
lj.begin
Write;
try
FStatus := 2;
s := 'TH1';
sleep(1978);
FStatus := 1;
finally
lj.EndWrite;
end;
end;
finally
lj.EndRead;
end;
end;

procedure th1.showresult;
begin
FMemo.Lines.Add(s);
end;

procedure th1.Execute ;
begin
while not terminateddo
begin
w;
Synchronize(showresult);
end;
end;

constructor th1.Create(Suspended:Boolean ;
Status : Integer ;
mem : TMemo);
begin
inherited Create(Suspended);
FreeOnTerminate:=True;
FStatus := Status;
FMemo := mem;
lj := TMultireadExclusiveWriteSynchronizer.Create;
end;

procedure th2.w;
begin
lj.begin
Read;
try
if FStatus = 1 then
begin
lj.begin
Write;
try
FStatus := 2;
sleep(500);
s := 'TH2';
FStatus := 1;
finally
lj.EndWrite;
end;
end
else
begin
s := 'Th2 can not run cause FStatus <> 1!';
end;
finally
lj.EndRead;
end;
end;

procedure th2.showresult;
begin
FMemo.Lines.Add(s);
end;

procedure th2.Execute ;
begin
while not terminateddo
begin
w;
Synchronize(showresult);
end;
end;

constructor th2.Create(Suspended:Boolean ;
Status : Integer ;
mem : TMemo);
begin
inherited Create(Suspended);
FreeOnTerminate:=True;
FStatus := Status;
FMemo := mem;
lj := TMultireadExclusiveWriteSynchronizer.Create;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
i := 1;
t1 := th1.Create(false,i,memo1);
t2 := th2.Create(false,i,memo1);
end;

end.
 
我知道为什么了，因为th1、th2中的FStatus它们是不同的变量....但怎么改呢？
 
根本搞不懂你在做什么？
首先，全局变量在哪里呀？FStatus只是线程内部的变量，创建一个线程对象，就有一个自己的FStatus变量，th1跟th2没看出来两者之间有任何联系，有任何同步互斥的必要！
其次，lj : TMultireadExclusiveWriteSynchronizer也是线程内部的变量，每创建一个线程，就新建了一个lj对象，那还谁跟谁同步呀，大家各管各的？怎么也要定义成全局变量才行的呀。
第三，只在需要访问共享资源的地方进行同步。
lj.begin
Write;
try
FStatus := 2;
sleep(500);
s := 'TH2';
FStatus := 1;
finally
lj.EndWrite;
end;
有必要这个样子吗？尤其还要Sleep转让控制权的。如果lj是全局的，如果其他线程也要写，那你这两个线程就死锁了
lj.begin
Write;
FStatus := 2;
lj.EndWrite;
sleep(500);
s := 'TH2';
lj.begin
Write;
FStatus := 1;
lj.EndWrite;
这样不就行了嘛。
第四，用CriticalSection完全就可以了，开销小，更有效率，没必要用TMultireadExclusiveWriteSynchronizer。
 
to chenshu_sc:
楼主的说的“全局变量”并是全局的，它们是对象内部成员，每个都占不同的空间。

按照楼主的设计思想，你应该在
var
Form1: TForm1;
FStatus : Integer;
//这个地方来定义全局变量
implementation
 
呵，都怪我没说清楚，还好　沙隆巴斯的主人　明白了我的意思：）
不过将FStatus改成Form1.i之后，th2好象一直无法执行，并CPU占用率一直是100%，这该怎么解决呢？
 
呵，搞定了，谢谢各位哈
 
多人接受答案了。
 
TO：lichengbin
　不好意思，分配错了，请到
　　http://www.delphibbs.com/delphibbs/dispq.asp?lid=3177747
　领取：）
　谢谢！
 
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