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Reference resources: http://blog.sina.com.cn/s/blog_605f5b4f0100x444.html

Note: precautions for fork to create multiple subprocesses at the same time in linux.

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It's an experiment, but it's good to have a network. Otherwise, many problems that you can't solve by yourself can't be solved. I first wrote a program to create multiple subprocesses (imitating the program to create a process in the book):

#include <stdio.h>#include <sys/types.h>#include <sys/wait.h>#include <stdlib.h>int main(void){ pid_t childpid1, childpid2, childpid3; int status; int num; childpid1 = fork(); childpid2 = fork(); childpid3 = fork(); if( (-1 == childpid1)||(-1 == childpid2)||(-1 == childpid3)) {  perror("fork()");  exit(EXIT_FAILURE); } else if(0 == childpid1) {  printf("In child1 process\n");  printf("\tchild pid = %d\n", getpid());  exit(EXIT_SUCCESS); }  else if(0 == childpid2)  {   printf("In child2 processd\n");   printf("\tchild pid = %d\n", getpid());   exit(EXIT_SUCCESS);  }   else if(0 == childpid3)   {    printf("In child3 process\n");    printf("\tchild pid = %d\n", getpid());    exit(EXIT_SUCCESS);   }    else    {     wait(NULL);     puts("in parent");   //  printf("\tparent pid = %d\n", getpid());   //  printf("\tparent ppid = %d\n", getppid());   //  printf("\tchild process exited with status %d \n", status);    } exit(EXIT_SUCCESS); }

The result is two zombies. I don't know how to figure them out. Finally, I found the answer on the Internet. And back and forth to figure out the methods and precautions:

#include <stdio.h>#include <sys/types.h>#include <sys/wait.h>#include <stdlib.h>int main(void){ pid_t childpid1, childpid2, childpid3; int status; int num;  /* You can't create a subprocess in a moment. You need to use * to create -] to judge -] to use -] to return or exit. Let alone test 2. C * childpid1 = fork(); * childpid2 = fork(); * childpid3 = fork()*/ childpid1 = fork();            //Establish if(0 == childpid1)            //judge {                     //Get into  printf("In child1 process\n");  printf("\tchild pid = %d\n", getpid());  exit(EXIT_SUCCESS);           //Sign out } childpid2 = fork(); if(0 == childpid2) {  printf("In child2 processd\n");  printf("\tchild pid = %d\n", getpid());  exit(EXIT_SUCCESS); } childpid3 = fork(); if(0 == childpid3) {  printf("In child3 process\n");  printf("\tchild pid = %d\n", getpid());  exit(EXIT_SUCCESS); } //wait(NULL) is not allowed here. Multiple subprocesses cannot wait with wait. It will only wait for one other to become a zombie waitpid(childpid1, NULL, 0); waitpid(childpid2, NULL, 0); waitpid(childpid3, NULL, 0); puts("in parent"); exit(EXIT_SUCCESS); }

By doing so strictly, there will be no zombies and no other process will be affected.

Create > judge > use > return or exit