信号、信号量、共有メモリを含む例

#include <stdio.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/sem.h>
#define SHMKEY1 (key_t)0x10
#define SHMKEY2 (key_t)0x15

#define SEMKEY  (key_t)0x20

#define SIZ 5*BUFSIZ


#define IFLAGS (IPC_CREAT|IPC_EXCL)
#define ERR ((struct databuf*)-1)
//p1,v1             
struct sembuf p1 = {0, -1, 0};
struct sembuf v1 = {0, 1, 0};
//p2,v1             
struct sembuf p2 = {1, -1, 0};
struct sembuf v2 = {1, 1, 0};
//                 
static int shmid1, shmid2, semid;
//            
struct databuf
{
    int d_nread;
    char d_buf[SIZ];
};


void fatal(char *mes)
{
      perror(mes);
      exit (1);
}
/**        ,    shmat     */
void getshm (struct databuf **p1, struct databuf **p2)
{      //      
      if ((shmid1=shmget(SHMKEY1, sizeof(struct databuf), 0600|IFLAGS)) < 0)
      {
        fatal ("shmget");
      }

      if ((shmid2=shmget(SHMKEY2, sizeof(struct databuf), 0600|IFLAGS)) < 0)
      {
        fatal ("shmget");
      }
      //  
      if ((*p1=(struct databuf*)(shmat(shmid1, 0, 0))) == ERR)
      {
        fatal("shmat");
      }

      if((*p2=(struct databuf*)(shmat(shmid2, 0, 0))) == ERR)
      {
        fatal("shmat");
      }

}

int getsem()
{
         //       2      ;
          if ((semid=semget(SEMKEY, 2, 0600|IFLAGS)) < 0)
          {
          fatal("segmet");
          }
          //      ,            
          if (semctl(semid, 0, SETVAL, 0) < 0)
          {
           fatal ("semctl");
          }
          //      ,           ,      
          //       
          if (semctl(semid, 1, SETVAL, 1) < 0)
          {
            fatal ("semctl");
          }

          return (semid);
}
//                 
void myremove()
{
      if (shmctl(shmid1, IPC_RMID, NULL) < 0)
      {
        fatal("shmctl");
      }
      if (shmctl(shmid2, IPC_RMID, NULL) < 0)
      {
        fatal("shmctl");
      }
      if (semctl(semid, 0, IPC_RMID, NULL) < 0)
         fatal("semctl");
       
      exit(0);
}

void reader(int semid, struct databuf *buf1, struct databuf *buf2)
{
      for(;;)
      {
       unsigned short val= semctl(semid,0,GETVAL,null);
       if(val<=0)
       {
         semop(semid,&v1,1);
       }
       else{
         //          
         semop(semid, &p1, 1)
       }
       //       ,  buf1->d_buf，
       //read           ，  0       ：   
       buf1->d_nread = read(0, buf1->d_buf, SIZ);
       //v  ,             
       semop(semid, &v1, 1);
      
       //p  ,          ,     ,          .
       semop(semid, &p2, 1);
     
       buf2->d_nread = read(0, buf2->d_buf, SIZ);
      //v  ,          
       semop(semid, &v2, 1);
     }
            
}

void writer(int semid, struct databuf *buf1, struct databuf *buf2)
{
      for(;;)
      {
        //p  ,              
        semop(semid, &p1, 1);
        //1       
        write(1, buf1->d_buf, buf1->d_nread);
        //          
        semop(semid, &v1, 1);
     
        //p  ,          ,     ,          .
        semop(semid, &p2, 1);
      
        write(1, buf2->d_buf, buf2->d_nread);
 
        semop(semid, &v2, 1);
                                                          }
}

int main()
{
      int semid, pid;
       
      struct databuf *buf1, *buf2;
     
      semid = getsem();
      getshm (&buf1, &buf2);

      switch(pid=fork())
      {
        case -1:
            fatal("fork");
            break;
        case 0:
            writer(semid, buf1, buf2);
            break;
        default:
       
        //           ctrl+c myremove      ,
        //       :     ,   .
        signal (SIGINT, myremove);
        reader(semid, buf1, buf2);
        break;
     }
      exit(0);
}