/* David A. Hess CS382 Dining Philosophers */

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/stat.h>
#include </usr/sys/sys/types.h>
#include </usr/sys/sys/ipc.h>
#include </usr/sys/sys/sem.h>
#include <errno.h>


extern int errno;

#define SEMPERM 0600

initsem();
p();
v();


int initsem(semkey,semvalue)
  key_t semkey;
  int *semvalue;
{
  int status = 0, semid;
	
  if((semid = semget(semkey,1,SEMPERM|IPC_CREAT|IPC_EXCL))==-1) {
    if(errno == EEXIST)
      semid = semget(semkey,1,0);
  }else
    status = semctl(semid,0,SETVAL,semvalue);
  if(semid == -1 || status == -1) {
    perror("initsem failed");
    return(-1);
  }else
    return semid;
}

int p(semid)
  int semid;
{
  struct sembuf p_buf;

  p_buf.sem_num = 0;
  p_buf.sem_op = -1;
  p_buf.sem_flg = SEM_UNDO;

  if(semop(semid, &p_buf, 1) == -1) {
    perror("p(semid) failed");
    exit(1);
  }else
    return(0);
}

int v(semid)
  int semid;
{
  struct sembuf v_buf;

  v_buf.sem_num = 0;
  v_buf.sem_op = 1;
  v_buf.sem_flg = SEM_UNDO;
	
  if(semop(semid, &v_buf, 1) == -1) {
    perror("v(semid) failed");
    exit(1);
  }else
		return(0);
}


main()
{
  int frk[5], room, i;
  key_t semkey = 0x200;
  int phil0id,phil1id,phil2id,phil3id,phil4id,retval;
  int semvalue = 1;

  for(i=0;i<5;i++) {
    if((frk[i] = initsem(semkey,&semvalue)) < 0) {
      printf("Error initializing frk[%d] semaphore\n",i);
      exit(1);
    }
    printf("frk[%d] initialized to semid %d\n",i,frk[i]);
    retval = semctl(frk[i],0,GETVAL,semvalue);
    printf("frk[%d] initialized to semvalue %d\n",i,retval);
    semkey += 0x010;
  }
  semvalue = 4;
  if((room = initsem(semkey,&semvalue)) < 0) {
    printf("Error initializing room semaphore\n");
    exit(1);
  }else
    printf("room initialized to semid %d\n",room);
    retval = semctl(room,0,GETVAL,semvalue);
    printf("room initialized to semvalue %d\n",retval);
  if((phil0id = fork()) < 0) {
    perror("phil 0 failed\n");
    exit(1);
  }else if(phil0id == 0)
    philosopher(0,frk,room);
  else if((phil1id = fork()) < 0) {
    perror("phil 1 failed\n");
    exit(1);
  }else if(phil1id == 0)
    philosopher(1,frk,room);
  else if((phil2id = fork()) < 0) {
    perror("phil 2 failed\n");
    exit(1);
  }else if(phil2id == 0)
    philosopher(2,frk,room);
  else if((phil3id = fork()) < 0) {
    perror("phil 3 failed\n");
    exit(1);
  }else if(phil3id == 0)
    philosopher(3,frk,room);
  else if((phil4id = fork()) < 0) {
    perror("phil 4 failed\n");
    exit(1);
  }else if(phil4id == 0)
    philosopher(4,frk,room);
  else {
    wait(0);
    printf("Time to stop. Now killing semaphores.\n");
    retval = semctl(room,0,IPC_RMID,4);
    for(i=0;i<5;i++)
      retval = semctl(frk[i],0,IPC_RMID,1);
  }
  exit(0);
}

int philosopher(i,frk,room)
  int i, frk[], room;
{
  int j,retval;

  for(j=0;j<10;j++) {
    printf("Philosopher %d is thinking.\n",i);
    sleep(1);
    p(room);
    p(frk[i]);
    p(frk[(i+1)%5]);
    printf("Philosopher %d is eating.\n",i);
    sleep(2);
    v(frk[i]);
    v(frk[(i+1)%5]);
    v(room);
  }
  exit(0);
}