实验要求

程序可以针对不同进程的请求进行判断，并决定是否满足其需求。算法程序需要设计合理的数据结构，对资源情况、进程相关数据进行存储。

内容

随机生成数据, 并校验数据是否会产生死锁问题

实现银行家算法的核心: 安全性算法, 银行家算法的请求判断

打印每个线程的合法请求向量序列

打印银行家算法一次接受的请求向量序列

代码

main.cpp

#include <iostream>
#include <pthread.h>
#include <stdlib.h>
#include <unistd.h>
#include <assert.h>
#include <stdbool.h>
#include <set>
#include <vector>
#include "myfunc.h"// 5 个进程, 3类资源
#define NUM_RESOURCES 3
#define NUM_PROCESSES 5
#define MAX_RES_NUM 10#define Lock(x) pthread_mutex_lock(x)
#define UnLock(x) pthread_mutex_unlock(x)// 因为只有一个资源分配处理器, 所以各线程需要互斥地申请资源
pthread_mutex_t mutex;
// 银行家算法需要用到的数据结构
std::vector<int> available(NUM_RESOURCES);
std::vector<std::vector<int>>maximum(NUM_PROCESSES, std::vector<int>(NUM_RESOURCES));
std::vector<std::vector<int>>need(NUM_PROCESSES, std::vector<int>(NUM_RESOURCES));
std::vector<std::vector<int>>allocation(NUM_PROCESSES, std::vector<int>(NUM_RESOURCES));
/*** 初始化可用资源
*/
void init_resources() {for (int i = 0; i < NUM_RESOURCES; i++) {// [0, MAX_RES_NUM]available[i] = rand() % MAX_RES_NUM + 1;}
}
/*** 初始化每个线程对每个资源的最大需求, 不超过available* (虽然本人绝对这个maximum和need没多大区别)
*/
void init_maximum() {for (int i = 0; i < NUM_PROCESSES; i++) {for (int j = 0; j < NUM_RESOURCES; j++) {// [0, available[j]]maximum[i][j] = rand() % (available[j] + 1);}}
}/*** 初始化分配矩阵* 初值为0 
*/ 
void init_allocation() {for (int i = 0; i < NUM_PROCESSES; i++) {for (int j = 0; j < NUM_RESOURCES; j++) {allocation[i][j] = 0;}}
}// 初始化需求矩阵
void init_need() {for (int i = 0; i < NUM_PROCESSES; i++) {for (int j = 0; j < NUM_RESOURCES; j++) {need[i][j] = maximum[i][j] - allocation[i][j];}}
}/*** 安全性算法:* 在某时刻, 查看当前可用资源向量面对, need矩阵是否处于安全状态* 即是否可以找到一个安全序列, 安全序列并不是唯一的, * 能找出一个安全序列即可证明当前的available处于安全状态
*/
std::vector<int> process_ids(NUM_PROCESSES);
bool check_safe() {// work是当前可分配的资源向量std::vector<int> work(available);// 保存安全序列(有必要可以打印调试)std::vector<int> safe_seq;std::set<int> pids(process_ids.begin(), process_ids.end());for (int i = 0; i < process_ids.size(); i++) {// 检查need矩阵的每一行, 如果该行对应的需求向量 <= workfor (auto pid : pids) {if (need[pid] <= work) {safe_seq.push_back(pid);work += allocation[pid];pids.erase(pid);break;}}}// 如果能找到一个包含所有线程的安全序列if (safe_seq.size() == process_ids.size()) {return true;}return false;
}
// path保存每个线程的请求向量
std::vector<std::vector<std::vector<int>>> path(NUM_PROCESSES);
// schedule保存处理器调度请求向量的顺序和对应的线程编号
std::vector<std::pair<int, std::vector<int>>> schedule;
/*** 向处理器发起资源分配请求* 利用银行家算法处理请求与分配
*/
void* request_banker(void *arg) {int process_id = *((int *)arg);while (true) {Lock(&mutex);// 随机为当前进程构造请求向量std::vector<int> request(NUM_RESOURCES);for (int i = 0; i < NUM_RESOURCES; i++) {request[i] = rand() % (need[process_id][i] + 1);}// 请求的资源 > 当前剩余的资源, // 则让出cpu, 重新生成一个合理的reqif (request > available) {UnLock(&mutex);continue;}// 如果随机生成的req=0, 则重新生成if (request == std::vector<int>(NUM_RESOURCES, 0)) {UnLock(&mutex);continue;}// 给当前线程分配资源for (int i = 0; i < NUM_RESOURCES; i++) {available[i] -= request[i];allocation[process_id][i] += request[i];need[process_id][i] -= request[i];}// 如果给当前进程分配了它所请求的资源// 但是进入了不安全的状态, 则撤销此次分配资源if (!check_safe()) {for (int i = 0; i < NUM_RESOURCES; i++) {available[i] += request[i];allocation[process_id][i] -= request[i];need[process_id][i] += request[i];}// 如果该请求向量, 会使得当前状态进入不安全的状态// 则该请求非法, 让其它线程请求printf("Process %d is Waiting\n", process_id);print_vector(need[process_id]);UnLock(&mutex);continue;} // 调试信息保存path[process_id].push_back(request);schedule.push_back(std::make_pair(process_id, request));if (need[process_id] == std::vector<int>(NUM_RESOURCES, 0)) {printf("Process %d have completed.\n", process_id);// 一个线程完成他的操作后要释放占用的资源❗❗❗❗available += allocation[process_id];for (auto p : path[process_id]) {print_vector(p);}UnLock(&mutex);// break使得该线程结束break;} UnLock(&mutex);}
}
/*** 检查是否满足银行家算法的先决条件* 假设有n个线程, m种资源, 每种资源k[i](i=0, ..., m-1)个* 使得不产生死锁的充分条件为: 每种资源的总需求和 <= n + m[i] - 1* 即满足该条件一定不会发生死锁, 但是不满足只是可能会产生死锁* 这里所谓死锁为: * 当前未完成的线程集合中的任意一个线程的任意一个请求都不能被银行家算法接受* 从而导致每个线程都在持续的做无用的请求* 例如: 当前有n=3个线程, m=1种资源, 数量为3* 每个线程的需求need如下*   alloc need avail* A:  0    1    3* B:  0    1* C:  0    4* 线程A最多请求1个资源, 如果满足线程A, 则剩余2个资源, 不能满足其余的线程, 进入不安全状态, 拒绝此请求* 线程B最多请求1个资源, 如果满足线程B, 则剩余2个资源, 不能满足其余的线程, 进入不安全状态, 拒绝此请求* 线程C最少请求一个资源, 如果满足线程C, 则剩余2个资源, * 如果接受C的下限请求, 下一个状态也为不安全状态*   alloc need avail* A:  0    1    2* B:  0    1* C:  1    3* 最终会不会发生死锁, 取决于调度, 如果敲好串行的调度这些线程的请求, * 则肯定不会发生死锁, 否则有可能发生
*/
bool check_prerequisite() {std::vector<int> colsum(NUM_RESOURCES);for (int i = 0; i < NUM_PROCESSES; i++) {int rowsum = 0;for (int j = 0; j < NUM_RESOURCES; j++) {if (maximum[i] == std::vector<int>(NUM_PROCESSES, 0)) {return false;}colsum[j] += maximum[i][j];rowsum += maximum[i][j];}if (rowsum == 0) return false;}for (int i = 0; i < NUM_RESOURCES; i++) {if (NUM_PROCESSES + available[i] - 1 > colsum[i]) {return false;}}return true;
}
void init() {init_resources();init_maximum();init_allocation();init_need();
}int main() {std::vector<pthread_t> threads(NUM_PROCESSES);srand(time(NULL));// 初始化互斥锁pthread_mutex_init(&mutex, nullptr);// 随机生成可用资源// 直到生成的数据不会发生死锁init_resources();printf("prerequisite[] => ");for (int i = 0; i < NUM_RESOURCES; i++) {printf("%d ", NUM_PROCESSES + available[i]);}printf("\n");// 保证生成的数据不会有死锁问题do {init_maximum();} while (check_prerequisite());init_allocation();init_need();printf("available[] => ");print_vector(available);printf("need[][] => \n");for (int i = 0; i < NUM_PROCESSES; i++) {print_vector(need[i]);}// 创建进程线程for (int i = 0; i < NUM_PROCESSES; i++) {process_ids[i] = i;pthread_create(&threads[i], nullptr, request_banker, &process_ids[i]);}// 等待所有线程结束for (int i = 0; i < NUM_PROCESSES; i++) {pthread_join(threads[i], nullptr);}printf("A safe cpu schedule: \n");for (auto [pid, req] : schedule) {printf("Process %d : ", pid);print_vector(req);}// 销毁互斥锁pthread_mutex_destroy(&mutex);return 0;
}

myfunc.h

#ifndef MYFUNC_H
#define MYFUNC_H#include <vector>
#include <stdio.h>
// 声明一个函数，用于比较两个 vector<int> 是否相等
void print_vector(std::vector<int> v);
bool operator==(const std::vector<int>& v1, const std::vector<int>& v2);
bool operator<=(const std::vector<int>& v1, const std::vector<int>& v2);
bool operator<(const std::vector<int>& v1, const std::vector<int>& v2);
bool operator>(const std::vector<int>& v1, const std::vector<int>& v2);
std::vector<int>& operator+=(std::vector<int>& v1, const std::vector<int>& v2);
std::vector<int>& operator-=(std::vector<int>& v1, const std::vector<int>& v2);
std::vector<int> operator+(const std::vector<int>& v1, const std::vector<int>& v2);
#endif

myfunc.cpp

#include "myfunc.h"
void print_vector(std::vector<int> v) {if (v.empty()) return;printf("[");for (int i = 0; i < v.size(); i++) {if (i != v.size() - 1) {printf("%d, ", v[i]);} else {printf("%d]\n", v[i]);}}
}
bool operator==(const std::vector<int>& v1, const std::vector<int>& v2) {// 检查向量的大小是否相等if (v1.size() != v2.size()) {return false;}// 逐个比较向量的元素for (std::size_t i = 0; i < v1.size(); ++i) {if (v1[i] != v2[i]) {return false;}}return true;
}
bool operator<=(const std::vector<int>& v1, const std::vector<int>& v2) {// 检查向量的大小是否相等if (v1.size() != v2.size()) {return false;}// 逐个比较向量的元素for (std::size_t i = 0; i < v1.size(); ++i) {if (v1[i] > v2[i]) {return false;}}return true;
}
bool operator>(const std::vector<int>& v1, const std::vector<int>& v2) {return !(v1 <=v2);
}
bool operator<(const std::vector<int>& v1, const std::vector<int>& v2) {// 检查向量的大小是否相等if (v1.size() != v2.size()) {return false;}// 逐个比较向量的元素for (std::size_t i = 0; i < v1.size(); ++i) {if (v1[i] >= v2[i]) {return false;}}return true;
}
std::vector<int>& operator+=(std::vector<int>& v1, const std::vector<int>& v2) {if (v1.size() != v2.size()) {throw nullptr;}for (std::size_t i = 0; i < v1.size(); ++i) {v1[i] += v2[i];}return v1;
}
std::vector<int>& operator-=(std::vector<int>& v1, const std::vector<int>& v2) {if (v1.size() != v2.size()) {throw nullptr;}for (std::size_t i = 0; i < v1.size(); ++i) {v1[i] -= v2[i];}return v1;
}
std::vector<int> operator+(const std::vector<int>& v1, const std::vector<int>& v2) {if (v1.size() != v2.size()) {return std::vector<int>();}std::vector<int> result;result.reserve(v1.size());for (std::size_t i = 0; i < v1.size(); ++i) {result.push_back(v1[i] + v2[i]);}return result;
}

运行结果与分析

保证没有死锁的数据, 运行结果

available[] => [2, 7, 1]
need[][] =>
[0, 3, 1]
[1, 3, 0]
[0, 0, 1]
[0, 5, 1]
[1, 0, 1]
Process 0 have completed.
[0, 3, 0]
[0, 0, 1]
Process 1 have completed.
[1, 3, 0]
Process 2 have completed.
[0, 0, 1]
Process 4 have completed.
[1, 0, 0]
[0, 0, 1]
Process 3 have completed.
[0, 5, 0]
[0, 0, 1]
A safe cpu schedule: 
Process 0 : [0, 3, 0]
Process 0 : [0, 0, 1]
Process 1 : [1, 3, 0]
Process 2 : [0, 0, 1]
Process 4 : [1, 0, 0]
Process 4 : [0, 0, 1]
Process 3 : [0, 5, 0]
Process 3 : [0, 0, 1]

修改程序片段为

do {init_maximum();} while (!check_prerequisite());

生成可能会产生死锁的数据, 但是没有调度出死锁的情况

available[] => [9, 8, 7]
need[][] =>
[2, 3, 6]
[6, 2, 2]
[7, 7, 2]
[4, 0, 0]
[2, 5, 7]
Process 0 is Waiting
[2, 3, 6]
Process 0 have completed.
[1, 1, 2]
[0, 0, 2]
[0, 2, 2]
[1, 0, 0]
Process 1 have completed.
[6, 2, 1]
[0, 0, 1]
Process 3 have completed.
[1, 0, 0]
[2, 0, 0]
[1, 0, 0]
Process 4 have completed.
[2, 5, 6]
[0, 0, 1]
Process 2 have completed.
[1, 3, 1]
[5, 4, 0]
[0, 0, 1]
[1, 0, 0]
A safe cpu schedule:
Process 0 : [1, 1, 2]
Process 0 : [0, 0, 2]
Process 0 : [0, 2, 2]
Process 0 : [1, 0, 0]
Process 1 : [6, 2, 1]
Process 1 : [0, 0, 1]
Process 3 : [1, 0, 0]
Process 3 : [2, 0, 0]
Process 3 : [1, 0, 0]
Process 4 : [2, 5, 6]
Process 4 : [0, 0, 1]
Process 2 : [1, 3, 1]
Process 2 : [5, 4, 0]
Process 2 : [0, 0, 1]
Process 2 : [1, 0, 0]

生成可能会产生死锁的数据, 调度出死锁的情况

available[] => [10, 6, 8]
need[][] => 
[2, 0, 5]
[4, 6, 3]
[6, 2, 1]
[5, 3, 2]
[4, 4, 8]
Process 0 is Waiting
[2, 0, 5]
Process 4 is Waiting
[4, 4, 8]
Process 4 is Waiting
[2, 4, 8]
Process 0 have completed.
[1, 0, 4]
[0, 0, 1]
[1, 0, 0]
.....
此后程序阻塞...