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876天前import java.util.ArrayList; |
import java.util.Scanner; |
/** |
* @className Banker |
* @Description 实验二 死锁的避免――银行家算法 |
* @date 2012-4-12 |
*/ |
public class Banker { |
int available[] = new int[] { 3, 3, 2 };// 可得到的资源 |
int max[][] = new int[][] { { 7, 5, 3 }, { 3, 2, 2 }, { 9, 0, 2 }, |
{ 2, 2, 2 }, { 4, 3, 3 } };// 每个进程最大资源数 |
int allocation[][] = new int[][] { { 0, 1, 0 }, { 2, 0, 0 }, { 3, 0, 2 }, |
{ 2, 1, 1 }, { 0, 0, 2 } };// 每个进程目前拥有的资源数 |
int need[][] = new int[][] { { 7, 4, 3 }, { 1, 2, 2 }, { 6, 0, 0 }, |
{ 0, 1, 1 }, { 4, 3, 1 } };// 每个进程需要的资源数 |
ArrayList<Integer> arrayList = new ArrayList<Integer>(); |
private void showData()// 展示数据输出每个进程的相关数据 |
{ |
System.out.println("进程个数：5 资源个数：3"); |
System.out.println("可用资源向量："); |
for (int i = 0; i < available.length; i++) { |
System.out.print(available[i] + "\t"); |
} |
System.out.print("\n最大需求矩阵Max:\n"); |
for (int i = 0; i < 5; i++) { |
for (int j = 0; j < 3; j++) { |
System.out.print(" " + max[i][j] + "\t"); |
} |
System.out.println(); |
} |
System.out.print("\n已分配矩阵Allocation:\n"); |
for (int i = 0; i < 5; i++) { |
for (int j = 0; j < 3; j++) { |
System.out.print(" " + allocation[i][j] + "\t"); |
} |
System.out.println(); |
} |
System.out.print("\n需求矩阵Need:\n"); |
for (int i = 0; i < 5; i++) { |
for (int j = 0; j < 3; j++) { |
System.out.print(" " + need[i][j] + "\t"); |
} |
System.out.println(); |
} |
} |
private boolean change(int inRequestNum, int inRequest[])// 分配数据 |
{ |
int requestNum = inRequestNum; |
int request[] = inRequest; |
// for(int i=0;i<3;i++)System.out.println("修改前available"+available[i]); |
if (!(request[0] <= need[requestNum][0] |
&& request[1] <= need[requestNum][1] && request[2] <= need[requestNum][2])) { |
System.out.println("出错：申请的资源大于需求值"); |
return false; |
} |
if ((request[0] <= available[0] && request[1] <= available[1] && request[2] <= available[2]) == false) { |
System.out.println("出错：无足够资源分配"); |
return false; |
} |
System.out.println("开始执行银行家算法..."); |
for (int i = 0; i < 3; i++)// 试分配数据给请求的线程 |
{ |
available[i] = available[i] - request[i]; |
allocation[requestNum][i] = allocation[requestNum][i] + request[i]; |
need[requestNum][i] = need[requestNum][i] - request[i]; |
} |
System.out.println("试分配完成...\n"); |
// for(int i=0;i<3;i++)System.out.println("修改后available"+available[i]); |
boolean flag = checkSafe(available[0], available[1], available[2]);// 进行安全性检查并返回是否安全 |
// System.out.println("安全性检查后"+flag); |
if (flag == true) { |
System.out.print("找到一个安全序列："); |
System.out.print(arrayList); |
System.out.println("\n已通过安全性测试！\n"); |
System.out.println("资源分配完成。"); |
return true; |
} else// 不能通过安全性检查 恢复到未分配前的数据 |
{ |
System.out.println("不能够安全分配,正在恢复..."); |
for (int i = 0; i < 3; i++) { |
available[i] = available[i] + request[i]; |
allocation[requestNum][i] = allocation[requestNum][i] |
- request[i]; |
need[requestNum][i] = need[requestNum][i] + request[i]; |
} |
System.out.println("恢复完成。"); |
return false; |
} |
} |
private boolean checkSafe(int a, int b, int c)// 安全性检查 |
{ |
System.out.println("进入安全性测试！"); |
arrayList.clear();// 先清空安全序列 |
int work[] = new int[3]; |
work[0] = a; |
work[1] = b; |
work[2] = c; |
int i = 0; |
boolean finish[] = new boolean[5]; |
while (i < 5)// 寻找一个能够满足的认为完成后才去执行下一进程 |
{ |
if (finish[i] == false && need[i][0] <= work[0] |
&& need[i][1] <= work[1] && need[i][2] <= work[2]) {// 找到满足的修改work值，然后i=0，重新从开始的为分配的中寻找 |
arrayList.add(i); |
for (int m = 0; m < 3; m++) |
work[m] = work[m] + allocation[i][m]; |
finish[i] = true; |
i = 0; |
} else |
// 如果没有找到直接i++ |
i++; |
} |
for (i = 0; i < 5; i++)// 通过finish数组判断是否都可以分配 |
{ |
if (finish[i] == false) |
return false; |
} |
return true; |
} |
public static void main(String[] args) { |
Banker bank = new Banker(); |
bank.showData(); |
int request[] = new int[3]; |
int requestNum; |
Scanner s; |
String choice = new String(); |
while (true)// 循环进行分配 |
{ |
s = new Scanner(System.in); |
System.out.println("请输入要请求的进程号（0--4）："); |
requestNum = s.nextInt(); |
System.out.println("输入请求资源的数目：按照这样的格式输入x x x："); |
for (int i = 0; i < 3; i++) { |
request[i] = s.nextInt(); |
} |
bank.change(requestNum, request); |
System.out.println("\n需要继续吗？ (y-继续/n-终止)"); |
choice = s.next(); |
while (true) { |
if (choice.equalsIgnoreCase("n")) { |
System.exit(1); |
} else if (choice.equalsIgnoreCase("y")) { |
break; |
} else { |
System.out.println("输入错误，请重试..."); |
System.out.println("\n需要继续吗？ (y-继续/n-终止)"); |
choice = s.next(); |
} |
} |
} |
} |
} |
