/**
   @version 1.20 1999-04-26
   @author Cay Horstmann
*/

/** 
   This program shows how to avoid data corruption 
   when multiple threads access a data structure
*/
public class SynchBankTest
{ 
   public static void main(String[] args)
   {  
      Bank b = new Bank(NACCOUNTS, INITIAL_BALANCE);
      int i;
      for (i = 0; i < NACCOUNTS; i++)
      {  
         TransferThread t = new TransferThread(b, i,
            INITIAL_BALANCE);
         t.setPriority(Thread.NORM_PRIORITY + i % 2);
         t.start();
      }
   }

   public static final int NACCOUNTS = 10;
   public static final int INITIAL_BALANCE = 10000;
}

/**
   A bank with a number of bank accounts.
*/
class Bank
{ 
   /**
      Constructs the bank.
      @param n the number of accounts
      @param initialBalance the initial balance
      for each account
   */
   public Bank(int n, int initialBalance)
   {  
      accounts = new int[n];
      int i;
      for (i = 0; i < accounts.length; i++)
         accounts[i] = initialBalance;
      ntransacts = 0;
   }

   /**
      Transfers money from one account to another.
      @param from the account to transfer from
      @param to the account to transfer to
      @param amount the amount to transfer
   */
   public synchronized void transfer(int from, int to, int amount)
      throws InterruptedException
   {  
      while (accounts[from] < amount)
         wait();
      accounts[from] -= amount;
      accounts[to] += amount;
      ntransacts++;
      notifyAll();
      if (ntransacts % NTEST == 0) test();
   }

   /**
      Prints a test message to check the integrity
      of this bank object.
   */
   public synchronized void test()
   {  
      int sum = 0;

      for (int i = 0; i < accounts.length; i++)
         sum += accounts[i];

      System.out.println("Transactions:" + ntransacts
         + " Sum: " + sum);
   }

   /**
      Gets the number of accounts in the bank.
      @return the number of accounts
   */
   public int size()
   {  
      return accounts.length;
   }

   public static final int NTEST = 10000;
   private final int[] accounts;
   private long ntransacts = 0;
}

/**
   A thread that transfers money from an account to other
   accounts in a bank.
*/
class TransferThread extends Thread
{  
   /**
      Constructs a transfer thread.
      @param b the bank between whose account money is transferred
      @param from the account to transfer money from
      @param max the maximum amount of money in each transfer 
   */
   public TransferThread(Bank b, int from, int max)
   {  
      bank = b;
      fromAccount = from;
      maxAmount = max;
   }

   public void run()
   {  
      try
      {  
         while (!interrupted())
         {  
            int toAccount = (int)(bank.size() * Math.random());
            int amount = (int)(maxAmount * Math.random());
            bank.transfer(fromAccount, toAccount, amount);
            sleep(1);
         }
      }
      catch(InterruptedException e) {}
   }

   private Bank bank;
   private int fromAccount;
   private int maxAmount;
}