/*
  NAME: 		shmreader
  SYNOPSIS: 	shmreader < inputfile 
  DESCRIPTION:
  This program communicate with another program 
  (shmwriter) using shared memory.
	This program reads the stdin into memory buffers and 
	the shmwriter writes the buffers into stdout.

*/


#include "def.h"

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

main()
{
    int i;

/*
  creat the shared memory segments and attach them
*/

    for (i = 0; i < 2; i++) {
        if ( (shmid[i] = shmget(SHMKEY + i, sizeof(BUFFER),
                                PERMS | IPC_CREAT)) < 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);
    }
/*
  create the two semaphores
*/


    if ( (fullbuf_sem = sem_create(SEMKEY1, 0)) < 0)
        printf("server: can't create client semaphore");
    if ( (emptybuf_sem = sem_create(SEMKEY2, 2)) < 0)
        printf("server: can't create server semaphore");


/*
  raed from stdin and write to memory
*/
		reader();
/*
  detach this shared memory and close the semaphores.
  the other program (shmwriter) is the last one to use
  the shared memory, so it'll remove it when it's done
*/

    for (i = 0; i < 2; i++) {
        if (shmdt((void *) buf[i]) < 0)
            printf("server: can't detach shared memory ");
    }

	
    sem_close(emptybuf_sem);
    sem_close(fullbuf_sem);
	
    exit(0);
}
    

reader()
{
    int i=0;
	

    while (1) {
        if (semaphore)
            sem_wait(emptybuf_sem);
        buf[i]->size = read(0, buf[i]->data, BSIZE);
        if (semaphore)
            sem_signal(fullbuf_sem);
/*        printf("Sending buffer of size = %d\n",buf[i]->size);*/
        if (buf[i]->size <=0)
            return;
        i ^= 1;
    }
}