/* readerswriters.c */
#include <signal.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <time.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <pthread.h>
#include "sem_ops.h"
#define READERS 8
#define WRITERS 3

int counter = 0;
int readers = 0;
int reader_sem;
int counter_sem;

void *writerfunc( void * arg ) { /* function for each thread */
  int *me;

  me = (int *) arg;

  srand( time( NULL ) );
  sleep( rand() % 5 );    /* delay a while */
  P( counter_sem );
  counter++;
  printf( "Writer Thread %d running!! counter = %d\n", *me, counter );
  V( counter_sem );

  pthread_exit( NULL );
}

void *readerfunc( void * arg ) { /* function for each thread */
  int *me;

  me = (int *) arg;

  P( reader_sem );
  readers++;
  if( readers == 1 )
    P( counter_sem );
  V( reader_sem );

  srand( time( NULL ) );
  sleep( rand() % 5 );    /* delay a while */
  printf( "Reader Thread %d running!! counter = %d\n", *me, counter );

  P( reader_sem );
  readers--;
  if( readers == 0 )
    V( counter_sem );
  V( reader_sem );

  pthread_exit( NULL );
}

int main( void ) {
  int i;
  pthread_t rtid[READERS];
  int readerid[READERS];
  pthread_t wtid[WRITERS];
  int writerid[WRITERS];

  counter = 0;
  reader_sem = semtran( IPC_PRIVATE );
  counter_sem = semtran( IPC_PRIVATE );
  V( counter_sem );    /* initialise to 1 */
  V( reader_sem );    /* initialise to 1 */

  for( i=0; i<READERS; i++ ) /* set up thread ids */
    readerid[i] = i;
  for( i=0; i<WRITERS; i++ ) /* set up thread ids */
    writerid[i] = i;
  for( i=0; i<WRITERS; i++ ) /* run the threads */
    pthread_create( &wtid[i], NULL, writerfunc, (void *) &writerid[i] );
  for( i=0; i<READERS; i++ ) /* run the threads */
    pthread_create( &rtid[i], NULL, readerfunc, (void *) &readerid[i] );
  for( i=0; i<WRITERS; i++ ) /* wait for them to finish */
    pthread_join( wtid[i], NULL );
  for( i=0; i<READERS; i++ ) /* wait for them to finish */
    pthread_join( rtid[i], NULL );
  return 0;
}