本次程式實現了通過訊號量來實現父程序與子程序互斥操作，當父程序執行列印操作時子程序被阻塞，當子程序執行列印操作時父程序阻塞。

實現程式碼如下:

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <string.h>
#include <signal.h>

int semId;
int SIZE = 1;

union semun {
               int              val;    /* Value for SETVAL */
               struct semid_ds *buf;    /* Buffer for IPC_STAT, IPC_SET */
               unsigned short  *array;  /* Array for GETALL, SETALL */
               struct seminfo  *__buf;  /* Buffer for IPC_INFO
                                           (Linux-specific) */
};

void Handle(int s){
  if(s == 2){
    semctl(semId,0,IPC_RMID);
    exit(0);
  }
}


int main(){
  signal(2,Handle);

  key_t key = ftok(".",4);
  semId = semget(key,1,IPC_CREAT | IPC_EXCL | 0666);
  
  union semun val;
  val.val = SIZE;

  if(semctl(semId,0,SETVAL,val) == -1){
    printf("semctl error!\n"); 
    exit(0);
  }

  struct sembuf p;
  p.sem_num = 0;
  p.sem_op = -1;
  p.sem_flg = 0;

  struct sembuf v = {0,1,0}; 

  if(fork() > 0){ 

    while(1){
      semop(semId,&p,1);
      printf("father go go go!!!\n");
      sleep(1);
      printf("father go go go!!!\n");
      sleep(1);
      printf("father go go go!!!\n");
      semop(semId,&v,1);
    }
  }

  else{
    while(1){ 
      semop(semId,&p,1);
      printf("child go go go!!!\n");
      sleep(1);
      printf("child go go go!!!\n");
      sleep(1);
      printf("child go go go!!!\n");
      semop(semId,&v,1);
    }
  }

  return 0;
}
 

實現結果如下: