/* chopsticks1.c

   chopstick management routines
   for Dining Philosophers example using processes

   This version uses usleep and busy-waiting in all processes.
   See also other version, which uses signals to wake up neighbors.

*/

#define _XOPEN_SOURCE 500
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <signal.h>
#include <time.h>
#include <sys/ipc.h>
#include <sys/signal.h>
#include <sys/stat.h>
#include <sys/types.h>

#include "chopsticks.h"

#define LOCKFILENAME_LENGTH 8

#define CHECK(CALL)\
 if ((CALL)) {\
    perror (#CALL);\
    exit (-1);\
 }

char * lockfilename[NTHREADS];
int    lockfd[NTHREADS];

void 
lock (int i) {
  int fildes;
  while ((fildes = open (lockfilename[i],
         O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR)) == -1) {
    if (errno != EEXIST) chopsticks_emergency_stop();
    CHECK (usleep (100)); /* sleep for 100 microseconds */
  }
  close (fildes);
}     

void
unlock (int i) {
  CHECK (unlink (lockfilename[i]) == -1);
}     

void
chopsticks_init() {
  int i;

  for (i = 0; i < NTHREADS; i++) {
     lockfilename[i] = (char *) malloc (LOCKFILENAME_LENGTH);
     memset ((void *) lockfilename[i], 0, LOCKFILENAME_LENGTH);
     sprintf (lockfilename[i], "LCK%d5", i);
  }
}
  
void
chopsticks_take (int i) {
  if (i == (NTHREADS - 1)) {
    lock (0);
    lock (NTHREADS - 1);
  } else {
    lock (i);
    lock ((i + 1) % NTHREADS);
  }
}

void
chopsticks_put (int i) {
  unlock (i);
  unlock ((i + 1) % NTHREADS);
}

void
chopsticks_finalize () {
   int i;
   for (i = 0; i < NTHREADS; i++) {
     unlink (lockfilename[i]);
     /* ignore result intentionally */
   }
}

void
chopsticks_emergency_stop() {
   fprintf (stderr, "*** EMERGENCY STOP***\n");
   chopsticks_finalize ();
   /* kill self and all other members of the current process group */
   kill (SIGKILL, 0);
   fprintf (stderr, "should never get here\n");
   exit (-1);
}