First Lombok Synchronized Example

I found some examples of Java programs that become deadlocked due to their incorrect use of the “synchronized” keyword. I decided to try to get them to work using the @Synchronized annotation provided by Project Lombok.

First, here is the example from the Really Big Tutorial.

package really.big.tutorial;

// from Really Big Tutorial:
// http://docs.oracle.com/javase/tutorial/essential/concurrency/deadlock.html

/**
 *
 * @author ericm
 */
public class Deadlock {

    static class Friend {
        private final String name;
        public Friend( String name ) {
            this.name = name;
        }
        public String getName() {
            return this.name;
        }
        public synchronized void bow( Friend bower ) {
            System.out.format("%s: %s has bowed to me!%n",
                this.name, bower.getName() );
            bower.bowBack( this );
        }
        public synchronized void bowBack( Friend bower ) {
            System.out.format("%s: %s has bowed back to me!%n",
                this.name, bower.getName() );
        }
    } // end class Friend

    public static void main( String[] args ) {
        final Friend alphonse = new Friend( "Alphonse" );
        final Friend gaston = new Friend( "Gaston" );
        new Thread( new Runnable() {
            public void run() { alphonse.bow( gaston ); }
        }).start();
        new Thread( new Runnable() {
            public void run() { gaston.bow( alphonse ); }
        }).start();
        System.out.println( "At the end of main" );
    } // end method main

} // end class Deadlock

Here is the same program with Lombok:

package really.big.tutorial;

// Lombok-ed refactoring of deadlock example from Really Big Tutorial:
// http://docs.oracle.com/javase/tutorial/essential/concurrency/deadlock.html

import java.util.UUID;
import lombok.Synchronized;

public class DeadlockLombok {

    static class Friend {
        private final Object readLock  = new Object[ 0 ];
        private final Object readLock2 = new Object[ 0 ];
        private final String name;
        public Friend( String name ) {
            this.name = name;
        }
        public String getName() {
            return this.name;
        }

        @Synchronized( "readLock" ) public  void bow( Friend bower ) {
            System.out.format( "%s: %s has bowed to me!%n",
                    this.name, bower.getName() );
            bower.bowBack( this );
        }

        // either one works
        // @Synchronized( "readLock2" ) public void bowBack( Friend bower ) {
        @Synchronized public void bowBack( Friend bower ) {
            System.out.format("%s: %s has bowed back to me!%n",
                    this.name, bower.getName() );
        }
    } // end class Friend

    public static void main( String[] args ) {
        final Friend alphonse = new Friend( "Alphonse" );
        final Friend gaston = new Friend( "Gaston" );
        new Thread(new Runnable() {
            public void run() { alphonse.bow( gaston ); }
        }).start();
        new Thread(new Runnable() {
            public void run() { gaston.bow( alphonse ); }
        }).start();

        System.out.println( "At the end of main" );
    } // end method main

} // end class DeadlockLombok

I will have a few more examples over the next few days.

Image from the Wikipedia page for Jakarta, a province in Indonesia. With Java, the name is usually based on coffee or Indonesia. Image assumed allowed under Fair Use.