银行家算法.txt

使用C++实现计算机操作系统中的银行家算法

#include<iostream.h>
struct PCB{
 char state;
 int request;
 int max;
 int allocation;
};
void randomallocation(struct PCB p[],int av);
bool safecheck(struct PCB p[],int av);
void bankallocation(struct PCB p[],int av);
void show(struct PCB p[],int av);
void showorder(int order[]);
void main()
{
    struct PCB process[3];
 int i;
 int j;
 int k;
    int available=10;
    for(i=0;i<3;i++)
 {
    cout<<endl;
    cout<<"p"<<i<<"->max: ";
    cin>>process[i].max;
    if(process[i].max>10)
    {
     cout<<endl;
     cout<<"错误,请重新输入!";
     i--;
    }
    else
    {
     do{
        cout<<endl<<"->allocation: ";
        cin>>process[i].allocation;
     }while((process[i].allocation>process[i].max)||
(available-process[i].allocation<0));
           available=available-process[i].allocation;
     process[i].request=0;
     process[i].state='R';
    }
 }
 show(process,available);
    cout<<endl<<"1--随机分配算法         2--银行家算法";
    do{
       cout<<endl<<"请选择: ";
       cin>>i;
    }while(!((i==1)||(i==2)));
    if(i==1)
       randomallocation(process,available);
    else
    {
       do{
          if(safecheck(process,available)==false)
    {
        cout<<endl<<"当前为不安全状态!";
              cout<<endl<<"       1--退出     2--重置";
     do{
     cout<<endl<<"选择: ";
     cin>>k;
     }while((k!=1)&&(k!=2));
    if(k==2)
    {
          available=10;
       for(j=0;j<3;j++)
    {
             cout<<endl<<"p"<<j<<"->allocation: ";
          cin>>process[j].allocation;
       available=available-process
[j].allocation;
    }
    }
    }
       else {k=0;break;}
    }while(k==2);
     if(k==1)return;
     else if(k==0)bankallocation(process,available);
 }
}
void showorder(int order[]){
   int i;
   cout<<endl<<"安全序列为: ";
   for(i=0;i<3;i++)
   {
       cout<<"p"<<order[i]<<"   ";
   }
  }
void show(struct PCB p[],int av){
   int i;
   cout<<endl<<"available="<<av;
   cout<<endl<<"number      max      request      allocation      
state";
   for(i=0;i<3;i++)
   {
     cout<<endl<<i;
    cout<<"            ";
    cout<<p[i].max;
    cout<<"            ";
    cout<<p[i].request;
    cout<<"            ";
    cout<<p[i].allocation;
    cout<<"            ";
    cout<<p[i].state;
    cout<<endl;
   }
}
void randomallocation(struct PCB p[],int av){
 int i=0;
 int j=0;
 int w;
 int e;
 while(1){
    if(i==3) i=i-3;
    while(1)
    {
       if(i==3)i=i-3;
    else
       if(p[i].state=='R')
    {
       do{
       cout<<endl<<"p"<<i<<"->request: ";
                cin>>p[i].request;
    }while(p[i].request>(p[i].max-p
[i].allocation));
    break;
    }
       else i++;
    }
       
    if(p[i].request<=av)
       {
    av=av-p[i].request;
    p[i].allocation=p[i].allocation+p[i].request;
    p[i].request=0;
    if(p[i].max==p[i].allocation)
    { 
    av=av+p[i].allocation;
    p[i].state='E';
    p[i].allocation=0;
    p[i].request=0;
   
    }
          j=0;
          while(j<3)
    {
     if((p[j].request<=av)&&(p[j].state=='W'))
              {
        av=av+p[j].allocation;
     p[j].request=0;
     p[j].state='E';
     p[j].allocation=0;
    
     }
     if((p[j].max<av+p[j].allocation)&&(p
[j].state=='W'))
     { 
     p[j].state='R';
     }
     
     j++;
    }
    show(p,av); 
    }
    else
    {
   p[i].state='W';
   show(p,av);
    }
    w=0;
    e=0;
    for(j=0;j<3;j++)
    {
    if(p[j].state=='W')
   w++;
    else if(p[j].state=='E')
   e++;
    else break;
    }
    
    if(((w+e)==3)&&(w!=0))
    {
    cout<<endl<<"发生死锁!";
         
    return;
    }
    else if(e==3)
    {
    cout<<endl<<"三个进程顺利执行完!";
 
       return;
    } 
    i++;
 }
}
void bankallocation(struct PCB p[],int av){
    int k;
 int request;
 int f;
 int i;
 show(p,av);
 while(1)
 {
    request=0;
    k=-1;
    do 
    {
     if(k!=-1)cout<<endl<<"不是安全状态!";
     av=av+request;         
           p[k].allocation=p[k].allocation-request;
     do{
     cout<<endl<<"p"<<"->NO.: ";
        cin>>k;
     }while(p[k].state!='R');
     do
     {
     cout<<endl<<"p"<<k<<"->request: ";
     cin>>request;
     }while(request>(p[k].max-p[k].allocation));
           if(request>av)
     {
        p[k].request=request;
     p[k].state='W';
     break;
     }
      p[k].allocation=p[k].allocation+request;
     av=av-request;
    }while(safecheck(p,av)!=true);
    if(p[k].allocation==p[k].max)
    {
     p[k].state='E';
     av=av+p[k].allocation;
           p[k].allocation=0;
    }
    for(i=0;i<3;i++)
    {
       if((p[i].state=='W')&&(p[i].request<=av))
    {
       if(safecheck(p,av)==true)
    {
        p[i].allocation=p[i].request+p
[i].allocation;
     av=av-p[i].request;   
  
     p[i].request=0;
     p[i].state='R';
     if(p[i].max==p[i].allocation)
     {
        p[i].state='E';
     av=av+p[i].allocation;
     p[i].allocation=0;
     }
    }
    else
    {
       cout<<endl<<"不是安全状态！原请求资源量无效
。";
       p[i].request=0;
    p[i].state='R';
    }
    }
    }
       show(p,av);
    f=0;
       for(i=0;i<3;i++)
    {
       if(p[i].state=='E')f++;
    }
    if(f==3)
    {
   cout<<endl<<"所有进程顺利执行完!"; 
      break;
    }
 }
}
bool safecheck(struct PCB p[],int av)
{
   bool finish[3];
   int order[3];
   int i;
   int j=0;
   int f=0;
   int k=0;
   int work;
   int temp;
   work=av;
   for(i=0;i<3;i++)
   {
      order[i]=0;
   if(p[i].state=='E')
    finish[i]=true;
   else
       finish[i]=false;
   }
   while(k<3){
   for(i=0;i<3;i++)
   {
   if((p[i].state=='W')&&(p[i].request<=work)&&(finish[i]
==false))
   {
         temp=p[i].allocation;
   p[i].allocation=p[i].request+p[i].allocation;
   }      
   if(((p[i].allocation+work)>=p[i].max)&&(finish[i]==false))
   {
   work=p[i].allocation+work;
   finish[i]=true;
   order[j]=i;
         j++;
         if(p[i].state=='W')p[i].allocation=temp;
   }
   }
   k++;
}
   for(i=0;i<3;i++)
      if(finish[i]==true)
    f++;
   if(f==3)
   {
    //showorder(order);
       return true;
   }
   else
     return false;
}