java银行家算法
时间: 2023-06-28 07:11:12 浏览: 41
银行家算法(Banker's algorithm)是一种避免死锁的算法,主要应用于操作系统中进程管理和资源分配。它是由艾兹格·迪杰斯特拉(Edsger W. Dijkstra)于1965年提出的。
下面是Java实现银行家算法的示例代码:
```java
public class BankerAlgorithm {
private int[][] allocation; // 分配矩阵
private int[][] max; // 最大需求矩阵
private int[][] need; // 需求矩阵
private int[] available; // 可用资源向量
private int processNum; // 进程数
private int resourceNum; // 资源种类数
public BankerAlgorithm(int[][] allocation, int[][] max, int[] available) {
this.allocation = allocation;
this.max = max;
this.available = available;
processNum = allocation.length;
resourceNum = available.length;
need = new int[processNum][resourceNum];
// 计算需求矩阵
for (int i = 0; i < processNum; i++) {
for (int j = 0; j < resourceNum; j++) {
need[i][j] = max[i][j] - allocation[i][j];
}
}
}
// 判断是否有足够的资源分配给进程
private boolean check(int processId, int[] request) {
for (int i = 0; i < resourceNum; i++) {
if (request[i] > need[processId][i] || request[i] > available[i]) {
return false;
}
}
return true;
}
// 分配资源给进程
public synchronized boolean allocate(int processId, int[] request) {
if (!check(processId, request)) {
return false;
}
for (int i = 0; i < resourceNum; i++) {
available[i] -= request[i];
allocation[processId][i] += request[i];
need[processId][i] -= request[i];
}
return true;
}
// 释放进程占用的资源
public synchronized void release(int processId) {
for (int i = 0; i < resourceNum; i++) {
available[i] += allocation[processId][i];
allocation[processId][i] = 0;
need[processId][i] = 0;
}
}
// 判断系统是否处于安全状态
public synchronized boolean isSafe() {
boolean[] finish = new boolean[processNum];
int[] work = new int[resourceNum];
// 初始化work向量
for (int i = 0; i < resourceNum; i++) {
work[i] = available[i];
}
// 检查每个进程是否可以完成
int count = 0;
while (count < processNum) {
boolean found = false;
for (int i = 0; i < processNum; i++) {
if (!finish[i] && check(i, need[i])) {
for (int j = 0; j < resourceNum; j++) {
work[j] += allocation[i][j];
}
finish[i] = true;
found = true;
count++;
}
}
if (!found) {
return false;
}
}
return true;
}
}
```
使用示例:
```java
int[][] allocation = {{0, 1, 0}, {2, 0, 0}, {3, 0, 2}, {2, 1, 1}, {0, 0, 2}};
int[][] max = {{7, 5, 3}, {3, 2, 2}, {9, 0, 2}, {2, 2, 2}, {4, 3, 3}};
int[] available = {3, 3, 2};
BankerAlgorithm banker = new BankerAlgorithm(allocation, max, available);
if (banker.isSafe()) {
System.out.println("系统处于安全状态");
} else {
System.out.println("系统处于不安全状态");
}
```
其中,allocation表示分配矩阵,max表示最大需求矩阵,available表示可用资源向量。在上面的示例中,我们使用银行家算法判断系统是否处于安全状态。如果系统处于安全状态,那么说明当前状态下不会发生死锁。反之,如果系统处于不安全状态,则需要采取措施避免死锁的发生。