/************************************************************
  File:          bridge.h
  Description:   A program that simulates a one-lane bridge
                 and some cars trying to get through it.

                 Declaration of the bridge monitor.
                                                         
  Author:        Dana Vrajitoru                          
  Organization:  IUSB                                    
  Date:          December 7, 2004
**************************************************************/

#ifndef BRIDGE_H
#define BRIDGE_H

#include <pthread.h>

// A monitor class for a single-lane bridge that can only be crossed
// in one direction. In this implementation, every car (thread)
// requesting to cross the bridge waits on a conditional
// variable. when the last car crosses the bridge in one direction, it
// allows all the cars waiting at that moment to cross in the opposite
// direction to cross the bridge. This is not necessarily a fair
// implementation.

class Bridge_monitor {
 private:
  pthread_mutex_t mutex;
  pthread_cond_t cond_left, cond_right;
  int crossing, waiting_left, waiting_right;
 public:
  // Simple init function setting all the values of the variables to
  // 0.
  void init();

  // A tread is calling these when it wants to cross the bridge to the
  // left or right respectively. If the bridge is not free, the thread
  // should be waiting on the appropriate conditional variable to be
  // allowed to cross the bridge.
  void request_left();
  void request_right();

  // A thread is calling these after it has finished crossing the
  // bridge. The last thread to cross should broadcast the conditional
  // variable in the opposite direction if any thread is waiting on
  // it, or the one in the same direction if not.
  void release_left();
  void release_right();
};

#endif