用JAVA多线程编程解决Lamport's Bakery问题

There are m customer threads and n salesperson threads. Each customer thread takes a rest for a random period of time, then enters the bakery and takes a number and waits (blocks) for the number to be called. Each salesperson thread serves the next waiting customer determined by number taken. Serving a customer takes a random amount of time. If there are no customers waiting to be served all salespersons go to sleep.

Write a solution to this problem.

问题解决.

import java.util.*;
import java.util.concurrent.*;
import java.util.concurrent.locks.*;

class Bakery
{
   Queue<Semaphore> customerqueue = new LinkedList<Semaphore>();//create queue for customer
   Lock lock = new ReentrantLock(); //define lock
   Condition bakeryStaffs = lock.newCondition();//define condition variable

public Bakery(){}

public void join(Semaphore sem)
{
    //lock function
    lock.lock();
    try
    {
        customerqueue.add(sem); //The customer make a queue
    }
    finally
   {
       lock.unlock();
   }

}

public void next()
{
    lock.lock();
    try
    {
        //If there no customer in bakery then the the staff will go to sleep
        if(customerqueue.size() == 0)
        {
             try
             {
                   bakeryStaffs.await();//Staff will sleep until customer call wake up
             }
             catch(InterruptedException e){}
       }

      //if customer queue size > 0 then staff will call customer come in bakery
      if(customerqueue.size()>0)
      {
            //Create customer queue
            //If customer have queue, than there will one by one enter bakery
            Semaphore s = customerqueue.poll();
            s.release();
      }  
   }
   finally
   {
         lock.unlock();
   }
}

//Call bakery staff wake up
public void call()
{
        lock.lock();

        //bakery staff call customer
        try
        {
               bakeryStaffs.signalAll();
        }
        finally
        {
              lock.unlock();
        } 
    }
}


class SalePerson extends Thread
{
       //Create variables
       Bakery hotbakery;
       int staffNumber;

       //Constructors
       public SalePerson(Bakery hb, int n)
       {
            hotbakery = hb;
            staffNumber = n;
       }

       public void run()
       {
              while(true)
              {
                   //Bakery staff waiting for customer
                   System.out.println(staffNumber + " Bakery Staff: I hava a rest");  
                   try
                   {
                          Thread.sleep(2000); 
                   }
                   catch(InterruptedException e){}

                   //Bakery staff call next customer
                   System.out.println(staffNumber + " Bakery staff: next customer!"); 
                   hotbakery.next(); 
              }
       }
}

class Customer extends Thread
{
         //variables
         Semaphore sem = new Semaphore(0);
         Bakery customer;
         int customerNumber;

         //Constructors
         public Customer(Bakery c, int cn)
         {
               customer = c;
               customerNumber = cn;
         }

         public void run()
         {
              //Customer join queue
              customer.join(sem);

              try
              {
                    //Create random waiting time
                    int t = (int)(Math.random()*10000);
                    Thread.sleep(t);
                    System.out.println(customerNumber + " Customer: I'm take a break!");

                     //customer call staff wake up 
                     customer.call();
                     System.out.println(customerNumber + " Customer: I go to bakery now!");;

                     //customer leaving
                     sem.acquire();
                     System.out.println(customerNumber + " Customer: I'm leaving");

             }
             catch(InterruptedException e){} 
       }
}

class BakeryTest
{
       public static void main(String args[])
       {
               Bakery bakery = new Bakery();

               //implement bakery staff threads
               for(int i=0; i<4; i++)
               {
                     new SalePerson(bakery,i).start();
               }

               //implement customer threads
              for(int i=0; i<10; i++)
              {
                    new Customer(bakery,i).start();
               }

               //create customer wait enter bakery time
               for(int j=0; j<10; j++)
               {
               try
               {
                      Thread.sleep(3000);
                }catch(InterruptedException e){}
          }
     }
}