银行家算法c语言绪论

银行家算法是一种避免死锁的算法，它通过动态地分配资源来避免进程死锁。下面是一个简单的银行家算法的C语言实现：

#include <stdio.h>
#include <stdbool.h>

#define P 5 // 进程数
#define R 3 // 资源数

int available[R] = {3, 3, 2}; // 可用资源
int max[P][R] = {{7, 5, 3}, {3, 2, 2}, {9, 0, 2}, {2, 2, 2}, {4, 3, 3}}; // 最大需求矩阵
int allocation[P][R] = {{0, 1, 0}, {2, 0, 0}, {3, 0, 2}, {2, 1, 1}, {0, 0, 2}}; // 已分配矩阵
int need[P][R]; // 需求矩阵
bool finish[P] = {false, false, false, false, false}; // 进程是否完成

void calculate_need() {
    for (int i = 0; i < P; i++) {
        for (int j = 0; j < R; j++) {
            need[i][j] = max[i][j] - allocation[i][j];
        }
    }
}

bool is_safe() {
    int work[R];
    for (int i = 0; i < R; i++) {
        work[i] = available[i];
    }
    bool finish_all = false;
    while (!finish_all) {
        bool can_allocate = false;
        for (int i = 0; i < P; i++) {
            if (!finish[i]) {
                bool can_finish = true;
                for (int j = 0; j < R; j++) {
                    if (need[i][j] > work[j]) {
                        can_finish = false;
                        break;
                    }
                }
                if (can_finish) {
                    can_allocate = true;
                    finish[i] = true;
                    for (int j = 0; j < R; j++) {
                        work[j] += allocation[i][j];
                    }
                }
            }
        }
        if (!can_allocate) {
            for (int i = 0; i < P; i++) {
                if (!finish[i]) {
                    return false;
                }
            }
            finish_all = true;
        }
    }
    return true;
}

void request_resources(int process_id, int request[]) {
    for (int i = 0; i < R; i++) {
        if (request[i] > need[process_id][i] || request[i] > available[i]) {
            printf("Error: Requested resources exceed the need or available resources.\n");
            return;
        }
    }
    for (int i = 0; i < R; i++) {
        available[i] -= request[i];
        allocation[process_id][i] += request[i];
        need[process_id][i] -= request[i];
    }
    if (is_safe()) {
        printf("Request approved.\n");
    } else {
        printf("Request denied. Rollback.\n");
        for (int i = 0; i < R; i++) {
            available[i] += request[i];
            allocation[process_id][i] -= request[i];
            need[process_id][i] += request[i];
        }
    }
}

int main() {
    calculate_need();
    int request[P][R] = {{0, 0, 0}, {0, 0, 0}, {0, 0, 0}, {0, 0, 0}, {0, 0, 0}}; // 请求资源矩阵
    int process_id;
    printf("Enter process id (0-4): ");
    scanf("%d", &process_id);
    printf("Enter request (e.g. 1 0 2): ");
    for (int i = 0; i < R; i++) {
        scanf("%d", &request[process_id][i]);
    }
    request_resources(process_id, request[process_id]);
    return 0;
}