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#include #include #include #include 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#include #include #include #include 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;}