编写多进程编程

实验内容：有3个进程，其中一个为父进程，其余两个是该父进程创建的子进程，其中一个子进程运行"ls -l"指令，另一个子进程暂停5s之后异常退出，父进程先用阻塞方式等待第一子进程的结束，然后用非阻塞方式等待另一个子进程退出，等待收集到第二个子进程结束的信息，父进程就返回。

/* multi_proc.c */
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/wait.h>

int main(void)
{
    pid_t child1, child2, child;
    
    /*创建两个子进程*/
    child1 = fork();        
    /*子进程1的出错处理*/
    if (child1 == -1)
    {
        printf("Child1 fork error\n");
        exit(1);
    }
    else 
        if (child1 == 0) /*在子进程1中调用execlp()函数*/
       {
           printf("In child1: execute 'ls -l'\n");
           if (execlp("ls", "ls", "-l", NULL) < 0)
           {
               printf("Child1 execlp error\n");
           }
       }
      else /*在父进程中再创建进程2，然后等待两个子进程的退出*/
      {
          child2 = fork();
          if (child2 == -1) /*子进程2的出错处理*/
          {
              printf("Child2 fork error\n");
              exit(1);
          }
          else if(child2 == 0) /*在子进程2中使其暂停5s*/
          {
              printf("In child2: sleep for 5 seconds and then exit\n");
            sleep(5);
            exit(0);
        }

        printf("In father process:\n");
        child = waitpid(child1, NULL, 0); /* 阻塞式等待 */
          if (child == child1)
          {
              printf("Get child1 exit code\n");
          }
          else
          {
              printf("Error occured!\n");
          }
          
          do
          {
              child = waitpid(child2, NULL, WNOHANG);/* 非阻塞式等待 */
              if (child == 0)
              {
                  printf("The child2 process has not exited!\n");
                  sleep(1);
              }
          } while (child == 0);
          
          if (child == child2)
        {
            printf("Get child2 exit code\n");
        }
        else
        {
            printf("Error occured!\n");
        }
    }
    return 0;
}

 第二种代码写法：

/* multi_proc_wrong.c */
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/wait.h>

int main(void)
{
    pid_t child1, child2, child;
    /*创建两个子进程*/
    child1 = fork();
    child2 = fork();
    /*子进程1的出错处理*/
    if (child1 == -1)
    {
        printf("Child1 fork error\n");
        exit(1);
    }
    else if (child1 == 0) /*在子进程1中调用execlp()函数*/
    {
             printf("In child1: execute 'ls -l'\n");
        if (execlp("ls", "ls", "-l", NULL) < 0)
        {
            printf("Child1 execlp error\n");
        }
      }
      
      if (child2 == -1) /*子进程2的出错处理*/
      {
          printf("Child2 fork error\n");
          exit(1);
      }
      else if( child2 == 0 ) /*在子进程2中使其暂停5s*/
      {
          printf("In child2: sleep for 5 seconds and then exit\n");
          sleep(5);
          exit(0);
      }
      else /*在父进程中等待两个子进程的退出*/
      {
          printf("In father process:\n");
          child = waitpid(child1, NULL, 0); /* 阻塞式等待 */
          if (child == child1)
          {
              printf("Get child1 exit code\n");
          }
          else
          {
              printf("Error occured!\n");
          }
          
          do
          {
              child = waitpid(child2, NULL, WNOHANG);/* 非阻塞式等待 */
              if (child == 0)
              {
                  printf("The child2 process has not exited!\n");
                  sleep(1);
              }
          } while (child == 0);
          
          if (child == child2)
        {
            printf("Get child2 exit code\n");
        }
        else
        {
            printf("Error occured!\n");
        }
    }
    return 0;
}