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){}
}
}
}
