SOURCE FILE: foodPass.cpp



/*     

In this program the server puts dishes full of food on one end of
a table and diners pass the dishes down to the other end of the
table where they are collected by the busser.

The job of each diner is to perform a loop:

1. become ready for the next dish, 

2. acquire the next dish on the trivet to the left, 

3. if the dish contains food eat some of the food from it,

4. when available, place the dish on the trivet to the right

5. if the dish contains the check then stop
   else go to step 1.

The job of the server is to serve dishes by placing them one
after another onto trivet 0 and then exit.

The job of the busser is to remove dishes from the last trivet
one after another until removing the check.

The threads implementing the server, busser, and diners have to
coordinate.  Their goals are to

1. avoid as much busy waiting as possible 

2. achieve as much parallel processing as possible

3. avoid the possibility that a person could acquire the same
   dish twice

4. avoid the possiblity that a person could "serve from an empty
   dish"

5. avoid the possibility that a person could place one dish on
   top of another.

6. make sure everyone gets finished eating and the check gets
   paid.

7. make sure that only two threads are involved in regulating
   access to each trivet: the thread that puts dishes onto the
   trivet and the thread that takes them off.

Your grade depends on how well you achieve these goals.

P.S. This program uses arrays and constants in a manner that
     allows for changing the number of places to put plates
     (trivets), the number of diners, and the number of 
     different courses (dishes) served to the diners.
     When you write code to synchronize the threads,
     you must also utilize arrays, and whatever else is
     required, to maintain that ability to change 
     the number of possible dishes, trivets, and diners.
 
*/

#include <iostream>
#include <sched.h>
#include <time.h>
#include <pthread.h>
#include <string>
#include "sem.h"

using namespace std ;

/* ######################################## */
/*             Misc Data Types              */
/* ######################################## */
     /* A data type - a struct with an int field 
        to represent a child ID at the program level. */
struct threadIdType
{
  int id ;
};

/* ######################################## */
/*             Global Variables             */
/* ######################################## */
//const int numTrivets = 6 ;
const int numTrivets = 3 ;
const int numDiners = numTrivets - 1 ;
const int maxDishNames = 13 ;
//const int numDishNames = 13 ;
const int numDishNames = 5 ;

int trivet[numTrivets] ;

string dishName[maxDishNames];

      /* Here declare the semaphores and other variables you will
         need to synchronize threads. */





      /* child_t are global variables to represent the
         dynamically-created threads. */

pthread_t child_t[numTrivets] ;

/* ######################################## */
/*      "Special"   Global Variables        */
/* ######################################## */

/* Code in sem.cpp "expects" the two variables below to be here.
   This particular program does not use "checking." */

         /* "Checking" is just a flag that you set to 1 if you want lots of
            debugging messages and set to 0 otherwise.  The semaphore code in
            sem.cpp imports "checking".  Therefore the semaphore operations
            will write lots of messages if you set checking=1.  */

int checking ; 

      /* In some programs, we use the "stdoutLock" variable declared below to
         get intelligible printouts from multiple concurrent threads that write
         to the standard output.  (There has to be something to prevent the
         output of the threads from interleaving unintelligibly on the standard
         output, and we can't use semaphores if the semaphore code is writing
         messages too.)

         To print a message to standard output, a thread first locks standard
         output, then writes, then unlocks standard output.  See files sem.cpp
         or conc.cpp for examples of code that write messages in this manner.

         WARNING:  DON'T change how the locking of standard output is done
         until you've thought a WHOLE lot about the consequences.  In
         particular, using semaphores to do the job of stdoutLock can cause
         "infinite recursion" under certain circumstances.  The reason is that
         the semaphore code itself imports "stdoutLock" and writes messages
         when the "checking" variable is set to 1. */

pthread_mutex_t stdoutLock ;

/* ################################################## */
/*                         init                       */
/* ################################################## */
void init() 
{
  int index ;

  srandom(time((time_t *) 0)); /* INITIALIZE RANDOM NUMBER GENERATOR */

  checking = 0 ;

       /* Initialize the "special lock" that is used only to get
          exclusive access to the screen. */

  if ( 0!=pthread_mutex_init(&stdoutLock, NULL) )
  {  cout << "MUTEX INITIALIZATION FAILURE!" << endl;
     exit(-1) ;}

    /* Initialize the trivets to indicate that each contains "no
       dish." */

  for (index=0; index<numTrivets; index++) trivet[index]=0;

    /* Here initialize the semaphores and other variables you use
       for synchronization.  */








 /* Give some mnemonic names to the dishes.  The first name is
    used for an empty trivet.  The last name denotes the check
    (bill) for the meal.  This is coded so no changes are needed
    here as long as the value of "numDishNames" is between 2 and
    13. */

  dishName[0]="no dish";
  dishName[1]="vegetable soup" ;
  dishName[2]="bread and butter" ;
  dishName[3]="beets and chickpeas" ;
  dishName[4]="hardboiled eggs" ;
  dishName[5]="calf tongue" ;
  dishName[6]="baked potato" ;
  dishName[7]="string beans" ;
  dishName[8]="rack of lamb" ;
  dishName[9]="salad" ;
  dishName[10]="coffee" ;
  dishName[11]="flan" ;
  dishName[numDishNames-1]="check" ;

}

/* ################################################## */
/*                    DelayAsMuchAs                   */
/* ################################################## */
void delayAsMuchAs (int limit)
{
  int time, step;
  time=(int)random()%limit;
  for (step=0;step<time;step++) sched_yield() ;
}

/* ################################################## */
/*                       Server                       */
/* ################################################## */
/*

     The mother thread spawns a child thread that executes this
     function.  This function carries out the job of the server
     at the restaurant.

*/
void * Server(void * ignore)
{
  int i, j, delayLimit=100 ;

  for (i=1; i<numDishNames; i++)
  {

        /* I delay a random time before I "feel like" placing
           another dish on the table.*/

    delayAsMuchAs(delayLimit);

      /* When the trivet is available, I place the dish on the
         trivet to my right. */

       /* Here do a synchronization task.  One thing you need to
          do is be sure that you are not going to place a dish on
          a trivet that alreay has a dish on it.  *DO NOT* just
          busy-wait until you see that the trivet is empty. */

    trivet[0]=i; // put dish #i onto trivet #0.
    pthread_mutex_lock(&stdoutLock) ;
    cout << "Server places " << dishName[trivet[0]] 
         << " on trivet #0." << endl ;
    pthread_mutex_unlock(&stdoutLock);

       /* Here you may want to a synchronization task --
          something that "opens the door" for diner #0 to get
          access to the new dish. */




  }
  pthread_exit ((void *)0) ;
}

/* ################################################## */
/*                         Diner                      */
/* ################################################## */
/*

     The mother thread spawns child threads that execute this
     function.  This function carries out the job of one of the
     diners at the restaurant.

*/

void * Diner(void * postnPtr)
{
       /* Type cast the parameter to recover "position" -- which
          tells me the position at which I am seated at the
          table. */
int position = ((threadIdType *)(postnPtr))->id ;

  int i, j, delayLimit=100 ;

  for (i=1; i<numDishNames; i++)
  {
        /* I delay a random time before I "feel like" picking up the next
           dish.*/

    delayAsMuchAs(delayLimit);
    
      /* When available, I pick up the next new dish on my left. */

       /* Here do a synchronization task.  One thing you need to
          do is be sure that there is a new dish on the trivet to
          your left now, and that the person on your left has
          "let go" of it. */




      /* I declare what I am doing */
    pthread_mutex_lock(&stdoutLock) ;
    cout << "Diner number "<< position ;
    if (i<numDishNames-1) cout << " enjoys ";
    else if (position<numDiners-1) cout << " examines " ;
         else cout << " examines and pays " ;
    
    cout << dishName[trivet[position]] << endl ;
    pthread_mutex_unlock(&stdoutLock);

        /* I delay a random time to simulate the time it takes for me to
           serve myself some of what is on the dish -- or look at the
           check. */

    delayAsMuchAs(delayLimit);

        /* When available, I place the dish on the trivet to my right. */

       /* Here do a synchronization task.  One thing you need to
          do is be sure that the trivet on your right does not
          have a dish on it now.*/




    pthread_mutex_lock(&stdoutLock) ;
    cout << "Diner number "<< position << " moves " 
         << dishName[trivet[position]] << " from trivet #"
         << position << " to trivet #" << position+1 << endl;
    pthread_mutex_unlock(&stdoutLock);
       /* transfer the dish on my left to trivet on my right */
    trivet[position+1]=trivet[position] ;
      /* mark trivet on my left as empty */
    trivet[position]=0;

       /* Here do a synchronization task. You have transferred a
          dish from your left to your right.  The person on your
          left will need to find out that the trivet on your left
          is now empty.  The person on your right will need to
          find out that the trivet on your right now has a new
          dish on it.  */



  }
  delete((threadIdType *)(postnPtr)) ;
  pthread_exit ((void *) 0) ;
}

/* ################################################## */
/*                       Busser                       */
/* ################################################## */
/*

     The mother thread spawns children and then executes this
     function.  This is convenient because this function should
     be the last to exit.  This function carries out the job of
     the busser at the restaurant.

*/
void * Busser (void * ignore)
{
  int i, j, delayLimit=100 ;

  for (i=1; i<numDishNames; i++)
  {
        /* I delay a random time before I "feel like" bussing another
           dish.*/

    delayAsMuchAs(delayLimit);

      /* When another dish is on the trivet to my right I remove it. */

       /* Here do a synchronization task.  One thing you need to
          do is be sure that there is a new dish on the trivet to
          your left now, and that the person on your left has
          "let go" of it. */



    pthread_mutex_lock(&stdoutLock) ;
    cout << "Busser removes "
         << dishName[trivet[numTrivets-1]] << " from trivet #"
         << numTrivets-1<< "." << endl ;
    pthread_mutex_unlock(&stdoutLock);
    trivet[numTrivets-1]=0; // remove the dish.

       /* Here do a synchronization task. The person on your left
          will need to find out that the trivet on your left is
          now empty.  */
  }
  return ignore ;
}

/* ################################################## */
/*                         Main                       */
/* ################################################## */
int main() 
{ 
    init(); 
  
    cout << endl << endl;
    cout << "Welcome to the restaurant!" << endl ;
    cout << numDiners << " will be dining." << endl ;
    cout << "The meal will consist of " << numDishNames-2 
         << " dishes." << endl;
    cout << "Bon appetite!" << endl ;
    cout << endl << endl;
  
    int i;
  
        /* This is a pointer to a struct that contains an int
          field - it is a convenient data type to use as the
          parameter to the child function.  */
    threadIdType * idPtr ; 
  
    for (i=0; i<numDiners; i++)
    {
          /* This records the current index as this child's ID */
       idPtr = new threadIdType ;
       idPtr->id = i ; 
  
       if (0!=pthread_create(&child_t[i], NULL, Diner, (void *) idPtr))
          {cout << "THREAD CREATION FAILURE!" << endl; exit(-1) ;}
       
       if (0!=pthread_detach(child_t[i]))
          {cout << "THREAD DETACHMENT FAILURE!" << endl ; exit(-1) ;}
    }
  
       if (0!=pthread_create(&child_t[numDiners], NULL, Server, (void *) 0))
          {cout << "THREAD CREATION FAILURE!" << endl; exit(-1) ;}
       
       if (0!=pthread_detach(child_t[numDiners]))
          {cout << "THREAD DETACHMENT FAILURE!" << endl ; exit(-1) ;}
        
    Busser((void *) 0) ;
  
    cout << endl << endl;
    cout << "Thank you for coming!" << endl ;
    cout << endl << endl;

    return 0 ;
}