操作系统之死锁检测算法：银行家算法

一、银行家算法

银行家是用来检测进程是否会发送死锁的一种算法，这是死锁避免的一种提前预防的机制。可以利用银行家算法进行系统安全进行一个预估。下面我将用一个案例来详细介绍银行家算法的过程。

二、银行家算法

#include 
 
int main(){
      int b = 0;
      int count = 0, m, n, process, temp, resource; 
      int allocation_table[5] = {0, 0, 0, 0, 0};
      int available[5], current[5][5], maximum_claim[5][5];
      int maximum_resources[5], running[5], safe_state = 0;
      printf("\n输入总共的进程数:\t");
      scanf("%d", &process);
      for(m = 0; m < process; m++) {
            running[m] = 1;
            count++;
      }
      printf("\n输入要分配的资源总数:\t");
      scanf("%d", &resource);
      printf("\n输入需要个数:\t");
      for(m = 0; m < resource; m++) { 
            scanf("%d", &maximum_resources[m]);
      }
      printf("\n输入分配资源表:\n");
      for(m = 0; m < process; m++) {
            for(n = 0; n < resource; n++) 
            {
                  scanf("%d", &current[m][n]);
            }
      }
      printf("\n输入最大需求表:\n");
      for(m = 0; m < process; m++) {
            for(n = 0; n < resource; n++) 
            {
                  scanf("%d", &maximum_claim[m][n]);
            }
      }
      printf("\n线程载体 \n");
      for(m = 0; m < resource; m++) {
            printf("\t%d ", maximum_resources[m]);
      }
      printf("\n 分配资源表\n");
      for(m = 0; m < process; m++) {
            for(n = 0; n < resource; n++) {
                  printf("\t%d", current[m][n]);
            }
            printf("\n");
      }
      printf("\n最大需求表 \n");
      for(m = 0; m < process; m++) {
            for(n = 0; n < resource; n++) {
                  printf("\t%d", maximum_claim[m][n]);
            }
            printf("\n");
      }
      for(m = 0; m < process; m++) {
            for(n = 0; n < resource; n++) {
                  allocation_table[n] = allocation_table[n] + current[m][n];
            }
      }
      printf("\n已经分配的资源 \n");
      for(m = 0; m < resource; m++) {
            printf("\t%d", allocation_table[m]);
      }
      for(m = 0; m < resource; m++) {
            available[m] = maximum_resources[m] - allocation_table[m];
      }
      printf("\n剩余资源:");
      for(m = 0; m < resource; m++) {
            printf("\t%d", available[m]);
      }
      printf("\n");
      while(count != 0) {
            safe_state = 0;
            for(m = 0; m < process; m++) {
                  if(running[m]) {
                        temp = 1;
                        for(n = 0; n < resource; n++) {
                              if(maximum_claim[m][n] - current[m][n] > available[n]) {
                                    temp = 0;
                                    break;
                              }
                        }
                        if(temp) {
                               printf("\n进程 %d 正在执行中 \n", m + 1);
                               running[m] = 0;
                               count--;
                               safe_state = 1;
                               for(n = 0; n < resource; n++) {
                                     available[n] = available[n] + current[m][n];
                               }
                               break;
                        }
                  }
            }
            if(!safe_state) {
                  printf("\n进程处于非安全状态 \n");
                  break;
            } 
            else {
                  printf("\n进程处于安全状态 \n");
                  printf("\n可用资源\n");
                  for(m = 0; m < resource; m++) 
                  {
                        printf("\t%d", available[m]);
                  }
                  printf("\n");
            }
      }
      return 0;
}