• 银行家算法


    一 银行家算法简介

         避免死锁
    

    二 代码实现

    package How_2;
    
    import java.awt.DisplayMode;
    import java.util.Arrays;
    import java.util.LinkedList;
    import java.util.Scanner;
    
    import javax.imageio.stream.MemoryCacheImageInputStream;
    
    import org.omg.CORBA.Request;
    
    class resource   //资源类
    {
        int []v;
        int []m;    // 当前剩余资源数组
        public resource(int[] v,int []m)
        {
            this.v=v;
           	this.m=m;  	
        }
    }
    class process   //进程类
    {
        static resource myResource;
        int id;               //进程标识
        int []max;            //最大需求量
        int []allocation;     //已分配量
        int []need;           //剩余需求量
        public process(resource myResource,int []max,int []allocation,int id)
        {
            this.myResource=myResource;	
            this.max=max;
            this.allocation=allocation;
            this.need=new int[max.length];
            this.id=id;
            for(int i=0; i<this.need.length; i++)
            {
                this.need[i]=this.max[i]-allocation[i];
            }
        }
    }
    class banker     //设置银行家
    {
       int  []Request;
       LinkedList<process> Process;
       int p;
       process thisprocess;
       String safeQueue="";                     //安全序列
       public banker(LinkedList myProcess)      //类资源
       {
           this.Process=myProcess;
           
       }
       public void request(int p,int []Request)      //资源请求
       {
           this.Request=Request;
           thisprocess=(process)Process.get(p);
           //判断请求合理性
           this.p=p;
           if(cheekM()&&cheekNeed())
           {
               //假设可以分配
               //更新m向量
               //不足:对矩阵运算符的重载
               for(int i=0; i<thisprocess.myResource.m.length; i++)
               {
                   thisprocess.myResource.m[i]-=Request[i];
                   thisprocess.need[i]-=Request[i];
                   thisprocess.allocation[i]+=Request[i];
    //			   System.out.println("77777777777777");
    //			   System.out.println("thisprocess.myResource.m["+i+"]"+thisprocess.myResource.m[i]);
               }
               if(cheekSafe())
               {
                   System.out.println("请求成功!");
                   System.out.println("安全序列为:");
                   System.out.println(safeQueue);
                   safeQueue="";
                   //更新状态
                   //更改need
                   //更改allocation
               }
               else  //不安全,拒绝分配
               {
                   System.out.println("此状态不安全,无法分配!!!");
                   for(int i=0; i<thisprocess.myResource.m.length; i++) //恢复资源状态
                   {
                       thisprocess.myResource.m[i]+=Request[i];
                       thisprocess.need[i]+=Request[i];
                       thisprocess.allocation[i]-=Request[i];
                   }
               }
           }
           display();
       }
       public  boolean cheekM()   					//检查当前资源是否满足要求,充足
       {
           boolean agree=true;
    //	   System.out.println("5555555555555555");
           for(int i=0; i<thisprocess.myResource.m.length; i++)
           {
               if(Request[i]>thisprocess.myResource.m[i])  //请求不合理
               {
                   agree=false;
                   System.out.println("资源不足,拒绝请求!!!");
                   break;
               }
    //		   System.out.println("Request["+i+"]="+Request[i]);
    //		   System.out.println(""+thisprocess.myResource.m[i]);
           }
           return agree;
       }
       public  boolean cheekNeed()   //检查请求是否合理
       {
           boolean agree=true;
           for(int i=0; i<thisprocess.need.length; i++)
           {
               if(Request[i]>thisprocess.need[i])  //请求不合理
               {
                   agree=false;
                   System.out.println("请求非法!!!");
                   break;
               }
    //		   System.out.println("66666666666666666666666666");
               System.out.println("Request["+i+"]="+Request[i]);
               System.out.println(""+thisprocess.need[i]);
           }
           return agree;
       }
       public  boolean cheekSafe()    //检查安全状态   核心代码
       {
           boolean agree=false;
           int []temp_m=new int [thisprocess.myResource.m.length];
           //System.out.println("复制数组");
           //复制数组
           temp_m=Arrays.copyOf(thisprocess.myResource.m, thisprocess.myResource.m.length);
           
           //复制链表    形成动态数组,这是银行家算法的关键
           //结束条件    数组变空   状态安全
           //结束条件    类似冒泡算法    只要有一次比较完temp_process的所以元素儿没有比m向量小的,此状态不安全
           //安全判断    v=m   资源可以全部收回
           
           LinkedList<process> temp_process=new LinkedList<process>();
           for(int i=0; i<Process.size(); i++)
           {
               temp_process.add(Process.get(i));
           }
    //	   System.out.println("进程"+1+":");
    //	   process itProcess=temp_process.get(1);
    //	   System.out.println("max[i]");
    //	   for(int ele:itProcess.max)
    //	   {
    //		   System.out.print(ele+"	");
    //	   }
           
    //	   System.out.println();;
    //	   for(int ele:temp_m)
    //	   {
    //		  System.out.print(""+ele+"	");
    //	   }
    //	   System.out.println();
           boolean count=true;
           do 
           {
               int i=0;
               count=false;
               for(i=0; i<temp_process.size(); i++)
               {
    //			   System.out.println("+++++++++++++++++++++++++++");
                   boolean yes=true;     //比较need
                   process itProcess1=(process) temp_process.get(i);
    //			   System.out.println("进程"+itProcess1.id);
                   //探查need矩阵
                   for(int j=0; j<temp_m.length; j++)
                   {
                       
                       if(itProcess1.need[j]>temp_m[j])
                       {
                           yes=false;
    //					   System.out.println("break");
                           break;
                       }
    //				   System.out.println("itProcess.need["+j+"]"+itProcess1.need[j]);
    //				   System.out.println("temp_m["+j+"]"+temp_m[j]);
                   }
    //			   System.out.println("max[i]");
    //			   for(int ele:itProcess1.max)
    //			   {
    //				   System.out.print(ele+"	");
    //			   }
    //			   System.out.println();
    //			   System.out.println("+++++++++++++++++++++++++++");
                   if(yes)  //need矩阵探查满足,开始回收此进程的allocation矩阵
                   { 
    //				   System.out.println("kkkkkkkkkkkkkkkkkkkkkkk");
                       for(int k=0; k<temp_m.length; k++)
                       {
                           temp_m[k]+=itProcess1.allocation[k];  //收回分配
                       }
    //				   for(int ele:temp_m)
    //				   {
    //					  System.out.print(""+ele+"	");
    //				   }
                       safeQueue+=""+temp_process.get(i).id;
                       count=true;
                       temp_process.remove(i); 
                       i=-1;
    // for循环重头开始           令i=-1 而不是让i=0
    // 否则会导致资源无法遍历  进程1				   
                   }
               }
           } 
           while(count&&!temp_process.isEmpty());                    //存在安全状态等价条件
    //	   if(Arrays.equals(temp_m, thisprocess.myResource.v))       //分配全部收回
    //	        数组相等
           if(count) 
           {
               agree=true;
           }
           return agree;
       }
       public void display()
       {
           System.out.println("m[i]:");
           for(int ele:thisprocess.myResource.m)
           {
               System.out.print(ele+"	");
           }
           System.out.println();
           for(int i=0; i<Process.size(); i++)
           {
             
               process itProcess=Process.get(i);
               System.out.println("进程"+itProcess.id+":");
               System.out.println("max[i]");
               for(int ele:itProcess.max)
               {
                   System.out.print(ele+"	");
               }
               System.out.println();
               System.out.println("allocation[i]");
               for(int ele:itProcess.allocation)
               {
                   System.out.print(ele+"	");
               }
               System.out.println();
               System.out.println("need[i]");
               for(int ele:itProcess.need)
               {
                   System.out.print(ele+"	");
               }
               System.out.println(); 
           }
       }
    }
    public class bin_1 
    {
        public static void main(String[] args) 
        {
            int v[]={10,5,7};    //总的资源数
            int m[]={3,2,2};     //剩余资源
            resource myResource=new resource(v,m);
            LinkedList<process> myProcesses=new LinkedList<process>();
            
            int max0[]={7,5,3};          //最大需求举证
            int allocation0[]={0,1,0};   //已分配资源
            process process0=new process(myResource, max0, allocation0,1);
            myProcesses.add(process0);
            
            int max1[]={3,2,2};
            int allocation1[]={2,1,0};
            process process1=new process(myResource, max1, allocation1,2);
            myProcesses.add(process1);
            
            int max2[]={9,0,2};
            int allocation2[]={3,0,2};
            process process2=new process(myResource, max2, allocation2,3);
            myProcesses.add(process2);
            
            int max3[]={2,2,2};
            int allocation3[]={2,1,1};
            process process3=new process(myResource, max3, allocation3,4);
            myProcesses.add(process3);
            
            int max4[]={4,3,3};
            int allocation4[]={0,0,2};
            process process4=new process(myResource, max4, allocation4,5);
            myProcesses.add(process4);
            
            
            
            banker myBanker=new banker(myProcesses);
            myBanker.display();
            
            Scanner how=new Scanner(System.in);
            int []zero={0,0,0};
            while(true)
            {
                int []myRequest=new int[m.length];
                int p;
                System.out.println("请输入请求进程:");
                p=how.nextInt();
                p--;   //下标从0开始
                System.out.println("请输入请求资源:");
                for(int i=0; i<myRequest.length; i++)
                {
                	myRequest[i]=how.nextInt();
                }
                myBanker.request(p, myRequest);
            }
        }
    }
    
    

    三 运行结果

    m[i]:
    3	2	2	
    进程1:
    max[i]
    7	5	3	
    allocation[i]
    0	1	0	
    need[i]
    7	4	3	
    进程2:
    max[i]
    3	2	2	
    allocation[i]
    2	1	0	
    need[i]
    1	1	2	
    进程3:
    max[i]
    9	0	2	
    allocation[i]
    3	0	2	
    need[i]
    6	0	0	
    进程4:
    max[i]
    2	2	2	
    allocation[i]
    2	1	1	
    need[i]
    0	1	1	
    进程5:
    max[i]
    4	3	3	
    allocation[i]
    0	0	2	
    need[i]
    4	3	1	
    请输入请求进程:
    2
    请输入请求资源:
    1
    0
    2
    Request[0]=1
    1
    Request[1]=0
    1
    Request[2]=2
    2
    请求成功!
    安全序列为:
    24135
    m[i]:
    2	2	0	
    进程1:
    max[i]
    7	5	3	
    allocation[i]
    0	1	0	
    need[i]
    7	4	3	
    进程2:
    max[i]
    3	2	2	
    allocation[i]
    3	1	2	
    need[i]
    0	1	0	
    进程3:
    max[i]
    9	0	2	
    allocation[i]
    3	0	2	
    need[i]
    6	0	0	
    进程4:
    max[i]
    2	2	2	
    allocation[i]
    2	1	1	
    need[i]
    0	1	1	
    进程5:
    max[i]
    4	3	3	
    allocation[i]
    0	0	2	
    need[i]
    4	3	1	
    请输入请求进程:
    

    四 总结收获

     1. 程序架构    
     class resource  //资源类
     class process   //进程类
     class banker     //设置银行家
     逐渐走入面向对象编程的方向
    2.  核心代码  使用过了Linkledist
    3.  核心代码 模仿改进版的冒泡排序
    

    五 不足
    .

    	 矩阵运算都使用for循环,应当考虑重载
    	 其次应该改进进程类的数据结构,使其拥有
    	 更强的健壮性
    	 可以考虑做gui界面
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  • 原文地址:https://www.cnblogs.com/Howbin/p/9941975.html
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