银行家算法的模拟程序

银行家算法是一种用于避免死锁的算法，它可以确保系统资源的安全分配。下面是一个简单的C++程序，用于模拟银行家算法：

#include <iostream>
#include <vector>
using namespace std;

const int MAX_PROCESS = 10;
const int MAX_RESOURCE = 10;

int available[MAX_RESOURCE];
int max_need[MAX_PROCESS][MAX_RESOURCE];
int allocation[MAX_PROCESS][MAX_RESOURCE];
int need[MAX_PROCESS][MAX_RESOURCE];
bool finish[MAX_PROCESS];

int num_process, num_resource;

bool is_safe() {
    vector<int> work(available, available + num_resource);
    vector<bool> finish(num_process, false);
    int count = 0;
    while (count < num_process) {
        bool found = false;
        for (int i = 0; i < num_process; i++) {
            if (!finish[i]) {
                bool can_finish = true;
                for (int j = 0; j < num_resource; j++) {
                    if (need[i][j] > work[j]) {
                        can_finish = false;
                        break;
                    }
                }
                if (can_finish) {
                    found = true;
                    finish[i] = true;
                    count++;
                    for (int j = 0; j < num_resource; j++) {
                        work[j] += allocation[i][j];
                    }
                }
            }
        }
        if (!found) {
            return false;
        }
    }
    return true;
}

bool request_resources(int process_id, int request[]) {
    for (int i = 0; i < num_resource; i++) {
        if (request[i] > need[process_id][i] || request[i] > available[i]) {
            return false;
        }
    }
    for (int i = 0; i < num_resource; i++) {
        available[i] -= request[i];
        allocation[process_id][i] += request[i];
        need[process_id][i] -= request[i];
    }
    if (is_safe()) {
        return true;
    } else {
        for (int i = 0; i < num_resource; i++) {
            available[i] += request[i];
            allocation[process_id][i] -= request[i];
            need[process_id][i] += request[i];
        }
        return false;
    }
}

int main() {
    cout << "Enter the number of processes: ";
    cin >> num_process;
    cout << "Enter the number of resources: ";
    cin >> num_resource;

    cout << "Enter the available resources: ";
    for (int i = 0; i < num_resource; i++) {
        cin >> available[i];
    }

    cout << "Enter the maximum needs of each process: ";
    for (int i = 0; i < num_process; i++) {
        for (int j = 0; j < num_resource; j++) {
            cin >> max_need[i][j];
            need[i][j] = max_need[i][j];
        }
    }

    cout << "Enter the current allocation of each process: ";
    for (int i = 0; i < num_process; i++) {
        for (int j = 0; j < num_resource; j++) {
            cin >> allocation[i][j];
            need[i][j] -= allocation[i][j];
        }
    }

    if (is_safe()) {
        cout << "The system is in a safe state." << endl;
    } else {
        cout << "The system is in an unsafe state." << endl;
    }

    int process_id;
    int request[MAX_RESOURCE];
    cout << "Enter the process ID and the resource request: ";
    cin >> process_id;
    for (int i = 0; i < num_resource; i++) {
        cin >> request[i];
    }
    if (request_resources(process_id, request)) {
        cout << "The request is granted." << endl;
    } else {
        cout << "The request is denied." << endl;
    }

    return 0;
}

该程序首先要求用户输入进程数和资源数，然后输入可用资源、每个进程的最大需求和当前分配情况。程序会检查系统是否处于安全状态，并允许用户输入进程ID和资源请求，然后检查该请求是否可以被满足。如果请求可以被满足，程序会更新资源分配情况并输出“请求已被授予”，否则输出“请求已被拒绝”。