/*
	shmWriter can be used with shmReader or with CopyFile.
	With CopyFile, it is the child process that writes the buffers into stdout.
	With shmReader, this program writes the buffers into stdout.
*/

#include "def.h"

BUFFER		 *buf[2];
int	shmid[2];
int semaphore =1;  /* it allows me to turn on and off the use of semaphores*/

int emptybuf_sem, fullbuf_sem;

main()
{
    int i;
/* 
   get the shared memory segments and attach it
   the parent must have already created it
*/
    for (i = 0; i < 2; i++) {
        if ( (shmid[i] = shmget(SHMKEY + i, sizeof(BUFFER), 0 )) < 0)
            printf("server: can't get shared memory %d", i);
        if ( (buf[i] = (BUFFER *) shmat(shmid[i], (char *) 0, 0))
             == (BUFFER *) -1)
            printf("server: can't attach shared memory %d", i);
    }
/*
  open the two semaphores.
  The parent must have already created it
*/
    if ( (fullbuf_sem = sem_open(SEMKEY1)) < 0)
        printf("server: can't open full  semaphore");
    if ( (emptybuf_sem = sem_open(SEMKEY2)) < 0)
        printf("server: can't create empty semaphore");
    writer();
      /*
       * Detach and remove the shared memory segments and
       * close the semaphores.
       */

    for (i = 0; i < 2; i++) {
        if (shmdt((void *) buf[i]) < 0)
            printf("client: can't detach shared memory ");
        if (shmctl(shmid[i], IPC_RMID, (struct shmid_ds *) 0) < 0)
            printf("client: can't remove shared memory ");
    }
      /*	
          sem_close(fullbuf_sem);
          sem_close(emptybuf_sem);*/
    sem_rm(fullbuf_sem);
    sem_rm(emptybuf_sem);	
    exit(0);
}
    
writer()
{
    int i=0;
    while (1) {
        if (semaphore)
            sem_wait(fullbuf_sem);
/*        printf("\n ... buff length =%d ...\n",buf[i]->size);fflush(stdout);*/
        write(1, buf[i]->data, buf[i]->size);
        if (buf[i]->size<=0)
            return;
        if (semaphore)
            sem_signal(emptybuf_sem);
        i ^= 1;
    }
}