银行家算法

一 概念

银行家算法是避免死锁的一种重要方法，本实验要求用高级语言编写和调试一个简单的银行家算法程序。加深了解有关资源申请、避免死锁等概念，并体会和了解死锁和避免死锁的具体实施方法。

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二 算法流程及数据结构

当用户申请一组资源时，系统必须做出判断，如果把这些资源分出去，系统是否还处于安全状态。若是，就可以分出这些资源；否则，该申请暂不予满足。
1．数据结构
假设有M个进程N类资源，则有如下数据结构：
MAX[M*N] M个进程对N类资源的最大需求量
AVAILABLE[N] 系统可用资源数
ALLOCATION[M*N] M个进程已经得到N类资源的资源量
NEED[M*N] M个进程还需要N类资源的资源量
2．银行家算法
设进程I提出请求Request[N]，则银行家算法按如下规则进行判断。
(1)如果Request[N]<=NEED[I，N]，则转(2)；否则，出错。
(2)如果Request[N]<=AVAILABLE，则转(3)；否则，出错。
(3)系统试探分配资源，修改相关数据：
AVAILABLE=AVAILABLE-REQUEST
ALLOCATION=ALLOCATION+REQUEST
NEED=NEED-REQUEST
(4)系统执行安全性检查，如安全，则分配成立；否则试探险性分配作废，系统恢复原状，进程等待。
3．安全性检查
(1)设置两个工作向量WORK=AVAILABLE；FINISH[M]=FALSE
(2)从进程集合中找到一个满足下述条件的进程，
FINISH[i]=FALSE
NEED<=WORK
如找到，执行(3)；否则，执行(4)
(3)设进程获得资源，可顺利执行，直至完成，从而释放资源。
WORK=WORK+ALLOCATION
FINISH=TRUE
GO TO 2
(4)如所有的进程Finish[M]=true，则表示安全；否则系统不安全。

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代码

import java.util.Scanner;public class BankerAlgorithm {    private int ProcessNum;     //进程数    private int ResourceNum;    //资源数    private int[] Available;    //每类资源可用数    private int[][] Max;        //每个进程度资源的最大需求数    private int[][] Need;       //每个进程还缺少的资源数    private int[][] Allocation;     //每个进程分到的资源数    public BankerAlgorithm(int processNum, int resourceNum) {                               //构造方法        System.out.println("请初始化数据：");        ProcessNum = processNum;        ResourceNum = resourceNum;        Allocation = new int[ProcessNum+1][ResourceNum+1];        Available = new int[ResourceNum+1];        Max = new int[ProcessNum+1][ResourceNum+1];        Need = new int[ProcessNum+1][ResourceNum+1];        Scanner input = new Scanner(System.in);        for ( int i = 1 ; i <= ProcessNum ; i++){            System.out.println("初始化进程"+i+"的数据：");            System.out.println("Max向量初始化:");            for ( int j = 1 ; j <= ResourceNum ; j++){                Max[i][j] = input.nextInt();            }            System.out.println("Allocation向量初始化：");            for ( int j = 1 ; j <= ResourceNum ; j++){                Allocation[i][j] = input.nextInt();                Need[i][j] = Max[i][j] - Allocation[i][j];            }        }        System.out.println("Available向量初始化：");        for ( int i = 1 ; i <= ResourceNum ; i++){            Available[i] = input.nextInt();        }        input.close();    }    public int getProcessNum() {        return ProcessNum;    }    public void setProcessNum(int processNum) {        ProcessNum = processNum;    }    public int getResourceNum() {        return ResourceNum;    }    public void setResourceNum(int resourceNum) {        ResourceNum = resourceNum;    }    public int[][] getNeed() {        return Need;    }    public int[] getAvailable() {        return Available;    }    public int[][] getAllocation() {        return Allocation;    }        public void Print(){                                                   //打印当前资源分配表        System.out.println("                资源分配表");        System.out.println("    Allocation    Max         Need      Available");        System.out.println("    r1 r2 r3    r1 r2 r3    r1 r2 r3    r1 r2 r3");        for ( int i = 1 ; i <= ProcessNum ; i++){            System.out.print(i+"    ");            for ( int j = 1 ; j <= ResourceNum ; j++){                System.out.print(" "+Allocation[i][j]);            }            System.out.print("      ");            for ( int j = 1 ; j <= ResourceNum ; j++){                System.out.print(" "+Max[i][j]);            }            System.out.print("      ");            for ( int j = 1 ; j <= ResourceNum ; j++){                System.out.print(" "+Need[i][j]);            }            System.out.print("      ");            for ( int j = 1 ; j <= ResourceNum ; j++){                System.out.print(" "+Available[j]);            }            System.out.println();        }    }    public int[] Apply_Request(){                                       //申请Request向量        Scanner in = new Scanner(System.in);        System.out.println("请输入Request向量");        int[] Request = new int[this.getResourceNum()+1];        for ( int i = 1 ; i <= getResourceNum() ; i++){            Request[i] = in.nextInt();        }        return Request;    }     public int Apply_Process(){                                        //输入要申请资源的进程        Scanner in = new Scanner(System.in);        System.out.println("请输入需要申请进程数(1-"+this.getProcessNum()+"):");        int process = in.nextInt();         return process;    }    public int Compare(int[] A , int[] B){                              //判断A向量是否小于等于B向量        int flag = 1;        if ( A.length == B.length){            for ( int i = 0 ; i < A.length ; i++){                if ( A[i] > B[i]){                    flag = 0;                    break;                }            }        }        return flag;    }    public int Judge_Request(int[] Request ,int process){                           //判断Ruqest向量是否大于Need向量或Available向量        int flag = 1;        for ( int i = 1 ; i <= this.getResourceNum() ; i++){            if ( Request[i] > this.getNeed()[process][i]){                flag = -1;                break;            }        }        if ( flag != -1){            flag = this.Compare(Request, this.Available);        }        return flag;    }    public void CarryOut(int flag ,int[] Request , int process){                //修改对应进程的资源分配        if ( flag == -1 ){              System.out.println("申请的Request向量出错!");        }        else{            if ( flag == 0){                System.out.println("进程"+process+"进入等待!");            }            else{                for ( int i = 1 ; i <= this.getResourceNum() ; i++){                    this.getAvailable()[i] -= Request[i];                    this.getAllocation()[process][i] += Request[i];                    this.getNeed()[process][i] -= Request[i];                }            }        }    }    public boolean IsAllTrue(boolean[] Finish){                             //判断Finish向量是否全为真        boolean flag = true;        for ( int i = 1 ; i < Finish.length ; i++){            if ( !Finish[i]){                flag = false;                break;            }        }        return flag;    }    public boolean Is_Safe(int process){                                //安全性算法以及安全序列        int[] Work = new int[this.getResourceNum()+1];        boolean[] Finish = new boolean[this.getProcessNum()+1];        int[] SafeSequence = new int[this.getProcessNum()+1];        int count = 1;              //Finish的下标计数器        int j = process;            //当前进程        for ( int i = 1  ; i <= this.getResourceNum() ; i++){               //对Work进行初始化            Work[i] = this.getAvailable()[i];        }        while( j <= this.getProcessNum()){                                      //判断安全性以及找出安全序列            for ( int i = 1 ; i <= this.getResourceNum() ; i++){                if ( Finish[j]){                    j++;                    break;                }                else if ( this.getNeed()[j][i] > Work[i]){                    j++;                    break;                }                else if( i == this.getResourceNum()){                    for ( int m = 1; m <= this.getResourceNum() ; m++){                        Work[m] += this.getAllocation()[j][m];                    }                    Finish[j] = true;                    SafeSequence[count++] = j;                    j = 1;                }            }        }        boolean issafe;        if (this.IsAllTrue(Finish)){                                            //输出安全序列            System.out.println("资源申请成功,安全序列为:");            System.out.print(SafeSequence[1]);            for ( int q = 2 ; q <= this.getProcessNum() ; q++){                System.out.print("->"+SafeSequence[q]);            }            System.out.println();            issafe = true;        }        else{            System.out.println("系统不安全，资源申请失败！");            issafe = false;        }        return issafe;    }    public void Rollback(int process , int[] Request){                          //当不安全是资源分配回滚        if ( !this.Is_Safe(process)){            for ( int i = 1 ; i <= this.getResourceNum() ; i++){                this.getAvailable()[i] += Request[i];                this.getAllocation()[process][i] -= Request[i];                this.getNeed()[process][i] += Request[i];            }        }    }    public void clear(int process){        for ( int i = 1 ; i <= this.getResourceNum() ; i++ ){            this.Available[i] += this.getAllocation()[process][i];            this.getAllocation()[process][i] = 0;        }    }    public void CarryBankerAlgorithm(){        Scanner in = new Scanner(System.in);        boolean SafeFlag = this.Is_Safe(1);        //初始化要申请资源的进程        int process =this.Apply_Process();                                          //初始化申请向量        int[] Request = this.Apply_Request();           //判断申请向量是否出错                    int RequestFlag = this.Judge_Request(Request, process);                         //进行修改相关数据        this.CarryOut(RequestFlag, Request, process);                                   //判断是否安全        SafeFlag = this.Is_Safe(process);                                           if ( !SafeFlag ){                                                                   //不安全就回复原来状态            this.Rollback(process, Request);        }        System.out.println("新时刻的资源分配表为：");        this.Print();    }    public static void main(String[] args) {        // TODO Auto-generated method stub        Scanner in = new Scanner(System.in);        System.out.println("请输入进程数与资源数：");                              //初始化进程数与资源数        int n = in.nextInt();        int m = in.nextInt();        //初始化数据            BankerAlgorithm bankeralgorithm = new BankerAlgorithm(n,m);                             bankeralgorithm.Print();        //执行银行家算法        bankeralgorithm.CarryBankerAlgorithm();                                 in.close();    }}