操作系统课程实验二 死锁的避免—银行家算法

[java]代码库

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();
				}
			}
		}
	}
}

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