Dining Philosophers Problem

[paeez]

can any one explain about the below code which is Dining Philosophers Problem..

//Dining Philosophers Problem
import java.util.Random;
class Monitor {
int phil_States[] = new int[5];   // 0=not_waiting, 1=waiting // 2=eating
boolean fork_States[] = new boolean[5];  // false = in use, true = free
Monitor() {        // constructor
   for(int i=0;i<5;i++) {
      phil_States[i]=0;
      fork_States[i]=true;
   }
}
synchronized void print_State()
{
System.out.println();        // newline
for(int i=0;i<5;i++)
     System.out.print(" " + phil_States[i]);        
}
synchronized void ask_to_eat(int pId)
{
   while(!fork_States[pId] || !fork_States[(pId+1)%4])
   {    // while it can't have both forks, wait
      phil_States[pId] = 1;  
      try 
  {wait();} 
  catch(InterruptedException e){} // it gets released
   }    // by a process doing a call to notify()
   phil_States[pId] = 2;  // eating
   fork_States[pId] = false;  // in use
   fork_States[(pId+1)%4] = false;
}
synchronized void ask_to_leave(int pId)
{
     fork_States[pId] = true; // available
     fork_States[(pId+1)%4] = true;
     phil_States[pId] = 0;  // thinking
     notify(); // free the Phil that has waited the longest
}
}
 
class Diners {
public static void main(String args[]) { // execution of the whole
   Monitor m = new Monitor(); // thing begins here
   Timer t = new Timer(m);  // make a new timer
   Phil p[] = new Phil[5];  // make an array of 5 refs to Phils
   for(int i=0; i<5; i++)
      p[i] = new Phil(i,m,t); // create the phils and start them
}
}
class Phil implements Runnable {
Monitor m;
Timer t;
Random r = new Random();  // Random number generator object
int pId;
float time;
Phil(int pId, Monitor m, Timer t) { // constructor
   System.out.println(pId + "is started: ");
   this.pId = pId;
   this.m = m;
   this.t = t;
   new Thread(this, "Phil").start(); // make a new thread and start it
}
public void run() {   // must override run, this is what
   for(int i=0; i<20; i++) {  // is executed when the thread starts
     m.ask_to_eat(pId);  // running
     time = 1000*r.nextFloat();
     try {Thread.sleep((int)time);} catch(Exception e){}
     m.ask_to_leave(pId);
     time = 1000*r.nextFloat();
     try {Thread.sleep((int)time);} catch(Exception e){}
   }
t.report_Stop();   // tell the timer this one is done
}       
}
class Timer implements Runnable {
Monitor m;
int completed;
Timer(Monitor m) {   // constructor
   this.m = m;
   new Thread(this, "Tim").start(); // make a new thread and start it
   completed=0;
}
public void report_Stop() {
   completed++;
}
public void run() {   // must override run(), this is 
   while(completed!=5) {  // what happens when the thread
      m.print_State();  // begins
      try {Thread.sleep(500);} catch(Exception e){}
   }
}
}

[Ezzaral]

Explain what about it? You haven't asked a question.

[paeez]

explain what it does..

[iamthwee]

Looks like a threaded program. What d you know about threads so far?

[Ezzaral]

explain what it does..

Well, I would say it is a possible solution to the Dining Philosophers problem, which one quick Google search provided the explanation: http://en.wikipedia.org/wiki/Dining_philosophers_problem

Are you wanting someone to walk you through how the code works step by step? I'm still not understanding what your question is exactly.

[jwenting]

seeing as the solution to the problem is contained in the official Sun tutorial, I wonder what the problem is :)

[ProgrammersTalk]

Check these tutorials, hopefully it will help you out
http://www.programmerstalk.net/thread845.html
http://www.cs.mtu.edu/~shene/NSF-3/e-Book/MUTEX/TM-example-philos-1.html
http://www.cs.utk.edu/~plank/plank/classes/cs560/560/notes/Dphil/lecture.html

Hopefully it would be helpful for you :)