/*
NAME: 		FileCopy
SYNOPSIS: 	FileCopy < inputfile > outputfile 
DESCRIPTION:
 	 This program commuincate 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;

main()
{
	int i;
        int status;
        pid_t pid;

/*
   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)
			perror("server: can't get shared memory %d", i);
		if ( (buf[i] = (BUFFER *) shmat(shmid[i], (char *) 0, 0))
							== (BUFFER *) -1)
			perror("server: can't attach shared memory %d", i);
	}
/*
   create the two semaphores
*/


	if ( (fullbuf_sem = sem_create(SEMKEY1, 1)) < 0)
		perror("server: can't create client semaphore");
	if ( (emptybuf_sem = sem_create(SEMKEY2, 0)) < 0)
		perror("server: can't create server semaphore");


/*
   fork a child to read from memory and write to stdout
*/
	if ( (pid = fork()) < 0)
		perror("fork error");
	else if (pid == 0) {
		sleep (1);
		if (execl ("./shmWriter", "shmwriter", NULL) < 0){
			perror("exec error");
			exit (-1);
		}
	} else

/*
  the parent raed from stdin and write to memory
*/
		reader();
/*
  wait for the child to finish writing the memory buffers
*/
	if (wait(&status) !=pid )
		perror("wait error");

/*
  detach ths shared memory and close the semahpores.
  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(buf[i]) < 0)
			perror("server: can't detach shared memory ");
	}

	sem_close(emptybuf_sem);
	sem_close(fullbuf_sem);

	exit(0);
}
    

reader()
{
	int i=0;
	

	sem_signal(emptybuf_sem);
	sem_signal(emptybuf_sem);

	while (1) {
		sem_wait(emptybuf_sem);
		buf[i]->size = read(0,buf[i]->data, BSIZE);
		sem_signal(fullbuf_sem);
		if (buf[i]->size <=0)
			break;
		i ^= 1;
	}
}