多线程模拟哲学家就餐问题
-----Amoon 2005/09/23
1）问题描述
学操作系统的进程同步都要涉及到三个经典问题：生产者-消费者问题、读者-写者问题和哲学家就餐问题。下面来介绍一下哲学家就餐问题： 哲学家就餐问题中，一组哲学家围坐在一个圆桌旁，每个哲学家的左边都只有一只筷子（当然他的右边也有一只筷子，但是这是他右边哲学家的左边的筷子），他们吃完了就思考，思考了一会就会饿，饿了就想吃，然而，为了吃饭，他们必须获得左边和右边的筷子。当每个哲学家只拿有一只筷子的时候，会坐者等另一只筷子，在每个哲学家都只拿一个筷子的时候，就会发生死锁。
2）关于源码的一点说明：
应用CRITICAL_SECTION 变量解决数据共享问题。
3）vc6下源码如下( 经作者在vc6下测试通过运行 ）：
#include <windows.h>
#include <process.h> /* _beginthread, _endthread */
#include <time.h>
#include <fstream>
#include <string>
#include <iostream>
#include <assert.h>
#include <time.h>
using namespace std;
ofstream out("out.txt");
BOOL b[6];//共享数据,用于表示 5 双筷子的使用情况,FALSE代表被占用
CRITICAL_SECTION cs;
class philosopher
{
private:
int m_num; //编号
int m_index; //标示装态,0-------waiting 1-----eating 2-----thinking
BOOL m_lhand; //true -----筷子空闲,false----筷子被占用
BOOL m_rhand;
public:
philosopher(int num=0) { m_num=num; m_index=2; m_lhand=TRUE; m_rhand = FALSE ;}
int GetNum() const { return m_num; }
int GetStatus() const { return m_index ; }
void ChangeStatus() ;
};
void philosopher::ChangeStatus()
{
EnterCriticalSection (&cs) ;
if(m_index==1) //eating----->thinking
{
assert(!b[m_num]);
b[m_num]=TRUE;
if( m_num==1)
{
assert(!b[5]);
b[5]= TRUE;
}
else
b[m_num-1]=TRUE;
m_index=2; // change to thinking
srand(time(NULL)*10000);
Sleep(rand()%10);
}
else if( m_index==2) //thinking
{
m_index=0; //change to waiting
}
else if( m_index==0) // waiting
{
if(m_num==1)
{
if(b[1]&&b[5])
{
b[1]=FALSE;
b[5]=FALSE;
m_index=1;
srand(time(NULL)*10000);
Sleep(rand()%10);
}
}
else
{
if(b[m_num]&&b[m_num-1])
{
b[m_num]= FALSE;
b[m_num-1]= FALSE;
m_index=1;
srand(time(NULL)*10000);
Sleep(rand()%10);
}
}
}
LeaveCriticalSection (&cs) ;
}
//ust to out the philosopher info
string PrintStatus(philosopher *pPh)
{
pPh->ChangeStatus();
int i=pPh->GetStatus();
string str;
if(i==0)
str="Waiting";
else if(i==1)
str="eating";
else str="thinking";
return str;
}
void ThreadFunc1(PVOID param)
{
while(1)
{
philosopher *pPh;
pPh=( philosopher *) param;
pPh->ChangeStatus();
}
}
void ThreadFunc2(PVOID param)
{
while(1)
{
philosopher *pPh;
pPh=( philosopher *) param;
pPh->ChangeStatus();
}
}
void ThreadFunc3(PVOID param)
{
while(1)
{
philosopher *pPh;
pPh=( philosopher *) param;
pPh->ChangeStatus();
}
}
void ThreadFunc4(PVOID param)
{
while(1)
{
philosopher *pPh;
pPh=( philosopher *) param;
pPh->ChangeStatus();
}
}
void ThreadFunc5(PVOID param)
{
while(1)
{
philosopher *pPh;
pPh=( philosopher *) param;
pPh->ChangeStatus();
}
}
int main()
{
for(int j=1;j<=5;j++) b[j]=TRUE;
out<<b[1]<<b[2]<<b[3]<<b[4]<<b[5];
philosopher ph1(1),ph2(2),ph3(3),ph4(4),ph5(5);
InitializeCriticalSection (&cs) ;
_beginthread(ThreadFunc1,0,&ph1);
_beginthread(ThreadFunc2,0,&ph2);
_beginthread(ThreadFunc3,0,&ph3);
_beginthread(ThreadFunc4,0,&ph4);
_beginthread(ThreadFunc5,0,&ph5);
cout<<"press ctrl+C to exit";
while(1)
{
out<<endl<<b[1]<<b[2]<<b[3]<<b[4]<<b[5]<<endl; // use to test
out<<"The status at :"<<clock()<<" ms "<<endl;
out<<"哲学家"<<ph1.GetNum() <<"所处状态:"<<ph1.GetNum()<<"--"<<PrintStatus(&ph1)<<endl;
out<<"哲学家"<<ph2.GetNum() <<"所处状态:"<<ph2.GetNum()<<"--"<<PrintStatus(&ph2)<<endl;
out<<"哲学家"<<ph3.GetNum() <<"所处状态:"<<ph3.GetNum()<<"--"<<PrintStatus(&ph3)<<endl;
out<<"哲学家"<<ph4.GetNum() <<"所处状态:"<<ph4.GetNum()<<"--"<<PrintStatus(&ph4)<<endl;
out<<"哲学家"<<ph5.GetNum() <<"所处状态:"<<ph5.GetNum()<<"--"<<PrintStatus(&ph5)<<endl;
Sleep(20);
}
DeleteCriticalSection (&cs) ;
return 0;
}
