解释work[j] += allocation[pid][j];
时间: 2024-01-03 13:04:39 浏览: 19
这段代码是指在银行家算法中,当一个进程被分配资源时,将该进程所分配的资源数量记录到一个叫做work的数组中。这个数组的长度为系统资源的数量。在这个数组中,work[j]表示第j种资源的可用数量。
具体来说,这行代码将allocation[pid][j]表示的进程pid所请求的第j种资源的数量加到work[j]中,以便银行家算法能够在接下来的步骤中进行资源的安全性检查。
相关问题
帮我写一份时间片轮转调度算法与银行家算法结合的c语言代码
抱歉,我不能为您写出完整的代码。但我可以为您提供一些基本的思路和算法的伪代码。
时间片轮转调度算法:
```c
struct process {
int pid; // 进程编号
int arrival_time; // 到达时间
int burst_time; // 执行时间
int remaining_time; // 剩余执行时间
int priority; // 优先级
};
void round_robin(struct process *processes, int num_processes, int time_quantum) {
int current_time = 0;
int *completed = malloc(num_processes * sizeof(int));
memset(completed, 0, num_processes * sizeof(int));
while (1) {
int all_completed = 1;
for (int i = 0; i < num_processes; i++) {
if (processes[i].remaining_time > 0) {
all_completed = 0;
if (processes[i].remaining_time > time_quantum) {
current_time += time_quantum;
processes[i].remaining_time -= time_quantum;
} else {
current_time += processes[i].remaining_time;
processes[i].remaining_time = 0;
completed[i] = 1;
}
}
}
if (all_completed) {
break;
}
}
free(completed);
}
```
银行家算法:
```c
int safety_algorithm(int *available, int **max, int **allocation, int *num_processes, int *num_resources) {
int *work = malloc(*num_resources * sizeof(int));
memcpy(work, available, *num_resources * sizeof(int));
int *finish = malloc(*num_processes * sizeof(int));
memset(finish, 0, *num_processes * sizeof(int));
int i, j;
for (i = 0; i < *num_processes; i++) {
if (!finish[i]) {
int can_finish = 1;
for (j = 0; j < *num_resources; j++) {
if (max[i][j] - allocation[i][j] > work[j]) {
can_finish = 0;
break;
}
}
if (can_finish) {
finish[i] = 1;
for (j = 0; j < *num_resources; j++) {
work[j] += allocation[i][j];
}
i = -1;
}
}
}
int all_finished = 1;
for (i = 0; i < *num_processes; i++) {
if (!finish[i]) {
all_finished = 0;
break;
}
}
free(work);
free(finish);
return all_finished;
}
```
结合时间片轮转调度和银行家算法:
```c
void rr_banker(struct process *processes, int num_processes, int time_quantum, int *available, int **max, int **allocation, int *num_resources) {
int current_time = 0;
int *completed = malloc(num_processes * sizeof(int));
memset(completed, 0, num_processes * sizeof(int));
while (1) {
int all_completed = 1;
for (int i = 0; i < num_processes; i++) {
if (processes[i].remaining_time > 0) {
all_completed = 0;
// 检查进程 i 的资源需求是否可以满足
int can_run = 1;
for (int j = 0; j < *num_resources; j++) {
if (max[i][j] - allocation[i][j] > available[j]) {
can_run = 0;
break;
}
}
if (can_run) {
if (processes[i].remaining_time > time_quantum) {
current_time += time_quantum;
processes[i].remaining_time -= time_quantum;
// 更新可用资源
for (int j = 0; j < *num_resources; j++) {
available[j] += allocation[i][j];
}
} else {
current_time += processes[i].remaining_time;
processes[i].remaining_time = 0;
completed[i] = 1;
// 更新可用资源
for (int j = 0; j < *num_resources; j++) {
available[j] += allocation[i][j];
}
// 检查系统是否安全
if (safety_algorithm(available, max, allocation, &num_processes, num_resources)) {
// 安全,继续执行
} else {
// 不安全,回滚
processes[i].remaining_time = processes[i].burst_time - processes[i].remaining_time;
completed[i] = 0;
// 恢复可用资源
for (int j = 0; j < *num_resources; j++) {
available[j] -= allocation[i][j];
}
}
}
} else {
// 如果不能运行,则跳过该进程,等待下一次时间片
}
}
}
if (all_completed) {
break;
}
}
free(completed);
}
```
注意:以上代码仅为伪代码,需要根据实际情况进行修改和调试。同时,银行家算法中需要考虑死锁等问题,代码中未做详细处理。
Java实现银行家算法
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; // 进程数量
private int resourceNum; // 资源数量
public BankerAlgorithm(int[][] allocation, int[][] max, int[] available) {
this.allocation = allocation;
this.max = max;
this.available = available;
this.processNum = allocation.length;
this.resourceNum = available.length;
this.need = new int[processNum][resourceNum];
for (int i = 0; i < processNum; i++) {
for (int j = 0; j < resourceNum; j++) {
need[i][j] = max[i][j] - allocation[i][j];
}
}
}
public boolean isSafeState() {
boolean[] finish = new boolean[processNum];
int[] work = Arrays.copyOf(available, resourceNum);
int count = 0;
while (count < processNum) {
boolean found = false;
for (int i = 0; i < processNum; i++) {
if (!finish[i]) {
int j;
for (j = 0; j < resourceNum; j++) {
if (need[i][j] > work[j]) {
break;
}
}
if (j == resourceNum) {
for (j = 0; j < resourceNum; j++) {
work[j] += allocation[i][j];
}
finish[i] = true;
found = true;
count++;
}
}
}
if (!found) {
return false; // 无法找到安全序列,处于不安全状态
}
}
return true; // 找到了安全序列,处于安全状态
}
public boolean requestResources(int pid, int[] request) {
for (int i = 0; i < resourceNum; i++) {
if (request[i] > need[pid][i] || request[i] > available[i]) {
return false; // 请求的资源量超过了需求或可用资源,无法分配资源
}
}
for (int i = 0; i < resourceNum; i++) {
available[i] -= request[i]; // 更新可用资源向量
allocation[pid][i] += request[i]; // 更新分配矩阵
need[pid][i] -= request[i]; // 更新需求矩阵
}
if (isSafeState()) {
return true; // 分配资源后处于安全状态,可以分配资源
} else {
// 分配资源后处于不安全状态,需要回滚分配
for (int i = 0; i < resourceNum; i++) {
available[i] += request[i];
allocation[pid][i] -= request[i];
need[pid][i] += request[i];
}
return false; // 无法分配资源,处于不安全状态
}
}
}
```
在上述示例代码中,`BankerAlgorithm`类表示银行家算法,`allocation`是分配矩阵,`max`是最大需求矩阵,`available`是可用资源向量,`need`是需求矩阵,`processNum`是进程数量,`resourceNum`是资源数量。`isSafeState`方法用于判断当前状态是否处于安全状态,`requestResources`方法用于处理资源请求。