/******************************************************************************
 * Solution for Lab Test 2 (lt2.c)                                            *
 * Written by Abhijit Das                                                     *
 * Date: November 03, 2009                                                    *
 ******************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/sem.h>

char *BUF;     /* shared buffer */
int M, X, Y;   /* ID for shared memory and semaphores */
FILE *fp;      /* Input file pointer for producer */
int DONE = 0;  /* Termination flag (not shared) */

#define P(s) semop(s,&pop,1)
#define V(s) semop(s,&vop,1)
struct sembuf pop, vop;

void init();    /* For Part 1 */
void produce(); /* For Part 2 */
void consume(); /* For Part 3 */
void ploop();   /* For Part 4 */
void cloop();   /* For Part 4 */
void windup();  /* For Part 5 */

/* Part 1: Initialization */
void init ()
{
   /* Create shared memory and semaphores */
   M = shmget(IPC_PRIVATE, 100*sizeof(char), 0777|IPC_CREAT);
   X = semget(IPC_PRIVATE, 1, 0777|IPC_CREAT);
   Y = semget(IPC_PRIVATE, 1, 0777|IPC_CREAT);

   /* Initialize the semaphores */
   semctl(X,0,SETVAL,0);
   semctl(Y,0,SETVAL,0);

   /* Initialize struct sembuf values for P() and V() */
   pop.sem_num = vop.sem_num = 0;
   pop.sem_flg = vop.sem_flg = 0;
   pop.sem_op = -1; vop.sem_op = 1;

   /* Fork the consumer process */
   if (fork()) {                           /* Parent the producer */
      fp = (FILE *)fopen("inp.txt", "r");  /* Open file pointer for reading */
      BUF = (char *)shmat(M,0,0);          /* Attach to shared memory */
      ploop();                             /* Enter production loop */
   } else {                                /* Child the consumer */
      BUF = (char *)shmat(M,0,0);          /* Attach to shared memory */
      cloop();                             /* Enter consumption loop */
   }
}

/* Part 2: The production primitive */
void produce ()
{
   int i;
   char c;

   i = 0; c = '\0';

   /* Read a line from the input file including the trailing new line char */
   while (c != '\n') {
      fscanf(fp, "%c", &c);
      if (feof(fp)) break;   /* feof() is true, after an fscanf() fails */
      BUF[i++] = c;
   }

   /* Terminate BUF by the null character */
   BUF[i] = '\0';

   /* If a line is read from the input file, then i >= 1, since at least the
      trailing new-line character is read. If i = 0, then EOF is reached, so
      terminate. */
   if (i == 0) DONE = 1;
}

/* Part 3: The consumption primitive */
void consume ()
{
   /* If a line (including the trailing new line) is written by the producer,
      the length of BUF is at least one. */
   if (strlen(BUF) >= 1) printf("Consumer: %s", BUF);
   else DONE = 1;
}

/* Part 4: synchronization of producer and consumer in the loops */

/* Production loop */
void ploop ()
{
   while (1) {
      produce();          /* Produce a line of text */
      V(Y);               /* Wake up the consumer */
      if (DONE) break;    /* If the input file is finished, return */
      P(X);               /* Wait for consumer to read buffer */
   }
}

/* Consumption loop */
void cloop ()
{
   while (1) {
      P(Y);               /* Wait for producer to finish writing */
      consume();          /* Print the buffer */
      if (DONE) exit(0);  /* All ines have come */
      V(X);               /* Wake up the producer for the next line */
   }
}

/* Part 5: Deletion of shared resources by the producer */
void windup ()
{
   wait(NULL);                 /* Wait for consumer to terminate */
   shmdt(BUF);                 /* Detach from shared memory */
   shmctl(M, IPC_RMID, 0);     /* Delete shared memory */
   semctl(X, 0, IPC_RMID, 0);  /* Delete semaphore */
   semctl(Y, 0, IPC_RMID, 0);  /* Delete semaphore */
}

int main ()
{
   init();
   windup();  /* Part 1 */
   exit(0);   /* Part 5 */
}

/******************************** End of lt2.c ********************************/