#include <stdio.h>#include <stdlib.h>#include <string.h>#include <sys/types.h>#include <sys/ipc.h>#include <sys/shm.h>#include <signal.h>#define SIZE 128void my_handler(int signo){}  int main(){   key_t shmkey;   int shmid;   pid_t pid;   char *head;      shmkey = ftok(".", 'a');   shmid = shmget(shmkey, SIZE, IPC_CREAT|0666);   head = shmat(shmid, 0, 0);   signal(SIGUSR1,my_handler);   while ( 1 )   {      if ( *((int *)head) == 0 )      {         usleep(500);      }      else      {         pid = *((int *)head);         break;      }   }   *((int *)head) = getpid();   while ( 1 )   {      printf("send message: ");      fgets(head+4, SIZE-4, stdin);      kill(pid, SIGUSR1);      pause();   }   return 0;}