Deadlock.java

package ar.com.javacuriosities.threads.liveness;

import java.util.concurrent.TimeUnit;

/*
 * Nos referimos a un deadlock cuando un thread espera por otro que esta utilizando un recurso (File, DB Table, etc), 
 * mientras que el otro thread también esta esperando por el primer thread que esta utilizando el recurso que este necesita
 */
public class Deadlock {

	public static void main(String[] args) {
		BankAccount account1 = new BankAccount(1, 100d);
		BankAccount account2 = new BankAccount(2, 100d);

		Thread transfer1 = new Thread(new TransferTask(account1, account2), "TransferTask-1");
		transfer1.start();

		Thread transfer2 = new Thread(new TransferTask(account2, account1), "TransferTask-2");
		transfer2.start();
	}

	private static final class TransferTask implements Runnable {
		private BankAccount from;
		private BankAccount to;

		public TransferTask(BankAccount from, BankAccount to) {
			this.from = from;
			this.to = to;
		}

		public void run() {
			System.out.println("Executing transfer from: " + from + " to: " + to);
			BankAccount.transfer(from, to, 10d);
		}
	}

	private static final class BankAccount {
		private int id;
		private double balance;

		public BankAccount(int id, double balance) {
			this.id = id;
			this.balance = balance;
		}

		public void withdraw(double amount) {
			// Simulamos algo de IO como por ejemplo acceso a una DB
			try {
				TimeUnit.MILLISECONDS.sleep(10);
			} catch (InterruptedException e) {
				// Log and Handle exception
				e.printStackTrace();
			}
			balance -= amount;
		}

		public void deposit(double amount) {
			// Simulamos algo de IO como por ejemplo acceso a una DB
			try {
				TimeUnit.MILLISECONDS.sleep(10);
			} catch (InterruptedException e) {
				// Log and Handle exception
				e.printStackTrace();
			}
			balance += amount;
		}

		@Override
		public String toString() {
			return "BankAccount [id=" + id + ", balance=" + balance + "]";
		}

		public static void transfer(BankAccount from, BankAccount to, double amount) {
			synchronized (from) {
				System.out.println("Lock acquired: " + from + " by" + Thread.currentThread().getName());
				from.withdraw(amount);
				synchronized (to) {
					System.out.println("Lock acquired: " + to + " by" + Thread.currentThread().getName());
					to.deposit(amount);
				}
			}
		}
	}
}