Question

求用JAVA语言编写的银行家算法的源代码

Answer 1

import java.util.*; class ThreadTest { static int type = 4, num = 10; //定义资源数目和线程数目 static int[] resource = new int[type]; //系统资源总数 //static int[] copyResource = new int[type]; //副本 static Random rand = new Random(); static Bank[] bank = new Bank[num]; //线程组 Bank temp = new Bank(); public void init() { //初始化组中每个线程，随机填充系统资源总数 for(int i = 0; i < type; i++) resource[i] = rand.nextInt(10) + 80; System.out.print("Resource:"); for(int i = 0; i < type; i++) System.out.print(" " + resource[i]); System.out.println(""); for(int i = 0; i < bank.length; i++) bank[i] = new Bank("#" + i); } public ThreadTest4() { init(); } class Bank extends Thread { //银行家算法避免死锁 public int[] max = new int[type], //总共需求量 need = new int[type], //尚需资源量 allocation = new int[type]; //已分配量 private int[] request = new int[type], //申请资源量 copyResource = new int[type]; //资源副本 private boolean isFinish = false; //线程是否完成 int[][] table = new int[bank.length][type*4]; //二维资源分配表 private void init() { // 随机填充总共、尚需、已分配量 synchronized(resource) { for(int i = 0; i < type; i++) { max[i] = rand.nextInt(5) + 10; need[i] = rand.nextInt(10); allocation[i] = max[i] - need[i]; resource[i] -= allocation[i]; //从系统资源中减去已分配的 } printer(); for(int i = 0; i < type; i++) { if(resource[i] < 0) { //若出现已分配量超出系统资源总数的错误则退出 System.out.println("The summation of Threads' allocations is out of range!"); System.exit(1); } } } } public Bank(String s) { setName(s); init(); start(); } public Bank() { //none } public void run() { try { sleep(rand.nextInt(2000)); } catch(InterruptedException e) { throw new RuntimeException(e); } while(true) { //程序没有完成时一直不断申请资源 if(askFor() == false) { try { sleep(1000); } catch(InterruptedException e) { throw new RuntimeException(e); } } else tryRequest(); if(noNeed() == true) break; } //休眠一段时间模拟程序运行 try { sleep(1000); } catch(InterruptedException e) { throw new RuntimeException(e); } System.out.println(getName() + " finish!"); synchronized(resource) { //运行结束释放占有资源 for(int i = 0; i < type; i++) { resource[i] += allocation[i]; need[i] = allocation[i] = max[i] = 0; } } } private void printer() { //打印当前资源信息 System.out.print(getName() + " Max:"); for(int i = 0; i < type; i++) System.out.print(" " + max[i]); System.out.print(" Allocation:"); for(int i = 0; i < type; i++) System.out.print(" " + allocation[i]); System.out.print(" Need:"); for(int i = 0; i < type; i++) System.out.print(" " + need[i]); System.out.print(" Available:"); for(int i = 0; i < type; i++) System.out.print(" " + resource[i]); System.out.println(""); } private boolean askFor() { //随机产生申请资源量并检测是否超标 boolean canAsk = false; for(int i = 0; i < type; i++) { request[i] = rand.nextInt(20); //防止申请量超过所需量 if(request[i] > need[i]) request[i] = need[i]; } for(int i = 0; i < type; i++) //防止随机申请资源全为0 if(request[i] > 0) canAsk = true; synchronized(resource) { //锁住可供资源检查是否超标 for(int i = 0; i < type; i++) { if(request[i] > resource[i]) //如果申请资源超过可供资源则等待一段时间后重新申请 return false; } } return canAsk; } private void tryRequest() { //创建副本尝试分配请求 synchronized(resource) { for(int i = 0; i < type; i++) //依然要防止请求量超出范围 if(request[i] > resource[i]) return; for(int i = 0; i < type; i++) { //复制资源量并减去需求量到一个副本上 copyResource[i] = resource[i]; copyResource[i] -= request[i]; } System.out.print(getName() + " ask for:"); for(int i = 0; i < type; i++) System.out.print(" " + request[i]); System.out.println(""); if(checkSafe() == true) { //如果检查安全则将副本值赋给资源量并修改占有量和需求量 for(int i = 0; i < type; i++) { resource[i] = copyResource[i]; allocation[i] += request[i]; need[i] -= request[i]; } System.out.println(getName() + " request succeed!"); } else System.out.println(getName() + " request fail!"); } } private boolean checkSafe() { //银行家算法检查安全性 synchronized(bank) { //将线程资源信息放入二维资源分配表检查安全性，0~ type可用资源／type~type*2所需资源／type* 2~type*3占有资源／type*3~-1可用+占用资源 for(int i = 0; i < bank.length; i++) { for(int j = type; j < type*2; j++) { table[i][j] = bank[i].need[j%type]; } for(int j = type*2; j < type*3; j++) { table[i][j] = bank[i].allocation[j%type]; } } //冒泡排序按需求资源从小到大排 for(int i = 0; i < bank.length; i++) { for(int j = i; j < bank.length-1; j++) { sort(j, 4); } } //进行此时刻的安全性检查 for(int i = 0; i < type; i++) { table[0][i] = copyResource[i]; table[0][i+type*3] = table[0][i] + table[0][i+type*2]; if(table[0][i+type*3] < table[1][i+type]) return false; } for(int j = 1; j < bank.length-1; j++) { for(int k = 0; k < type; k++) { table[j][k] = table[j-1][k+type*3]; table[j][k+type*3] = table[j][k] + table[j][k+type*2]; if(table[j][k+type*3] < table[j+1][k+type]) return false; } } } return true; } private void sort(int j, int k) { //递归冒泡排序 int tempNum; if(table[j][k] > table[j+1][k]) { for(int i = type; i < type*2; i++) { tempNum = table[j][i]; table[j][i] = table[j+1][i]; table[j+1][i] = tempNum; } /*temp = bank[j]; bank[j] = bank[j+1]; bank[j+1] = temp;*/ } else if(table[j][k] == table[j+1][k] && k < type*2) //此资源量相同时递归下一个资源量排序并且防止超出范围 sort(j, k+1); } private boolean noNeed() { //是否还需要资源 boolean finish = true; for(int i = 0; i < type; i++) { if(need[i] != 0) { finish = false; break; } } return finish; } } public static void main(String[] args) { ThreadTest t = new ThreadTest(); //后台线程，设定程序运行多长时间后自动结束 new Timeout(30000, "---Stop!!!---"); } }