/* =================================================================
   Reader/writer
   ================================================================= */

#include <iostream.h>
#include <stdlib.h>
#include <pthread.h>
#include <synch.h>

#define NIter   1000
#define MAX 10

int nItems = 0;     // Number of items in buffer
int buf[MAX];
int writePtr = 0, readPtr = 0;

sema_t writerSem, readerSem;

void *writerProc(void *arg)
{
   int i, x, sum;

   sum = 0;

   for ( i = 0; i < NIter; i++ )
   {
      x = rand()%100;               // Produce an item

      sum += x;

      sema_wait(&writerSem);   
      cout << "+";

      buf[writePtr] = x;             // Put x in buffer      
      writePtr = (writePtr+1) % MAX; 

      sema_post(&readerSem);   
   }

   cout << "Writer: sum = " << sum << "\n\n";

   return NULL;
}


void *readerProc(void *arg)
{
   int i, x, sum;

   sum = 0;

   for ( i = 0; i < NIter; i++ )
   {
      sema_wait(&readerSem);
      cout << "-";

      x = buf[readPtr];             // get x from buffer
      sum += x;
      readPtr = (readPtr+1) % MAX;

      sema_post(&writerSem);   
   }

   cout << "Reader: sum = " << sum << "\n\n";

   return NULL;
}



/* =======================
   MAIN
   ======================= */

int main(int argc, char *argv[])
{
   int i, num_threads;
   pthread_t tid[2];	/* Thread ID used for thread_join() */

   /* =========================
      Initialize semaphore
      ========================= */
// sema_init( &writerSem,   1, NULL, NULL );    /* Interesting experiment */

   sema_init( &writerSem, MAX, NULL, NULL );
   sema_init( &readerSem,   0, NULL, NULL );

   /* ------
      Create threads
      ------ */
   if ( pthread_create(&tid[0], NULL, readerProc, NULL) )
   {
      cout << "Cannot create READER thread" << endl;
      exit(1);
   }

   if ( pthread_create(&tid[0], NULL, writerProc, NULL) )
   {
      cout << "Cannot create WRITER thread" << endl;
      exit(1);
   }


   cout << "Main thread is waiting...." << endl;
   for (i = 0; i < 2; i = i + 1)
      pthread_join(tid[i], NULL);
   cout << "Main thread is DONE...." << endl;
}