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IdentityHashMap Implementation

/**
 * IdentifyHashMap  - 
 *   - Implements Map Interface with a hash table using reference-equality instead of object-equality when comparing keys.
 *    Eg:  if ( k1 == k2 ) unlike HashMap equality if( K1 == null ? k2 ==null : k1.equals(k2)).
 *   - It's not a general purpose implementation and designed to use only in rare cases where reference-equality semantics are required
 *   - Use cases like topology-preserving object graph, deep-copying, adding application shutdown hook.
 *   - This Map is not synchronized.  To synchronize use Collections SynchronizedMap
 *       Map identifyHashMap = Collections.synchronizedMap( new IdentifyHashMap(..)) ; 

 *
 */


import java.util.Collection;
import java.util.IdentityHashMap;

public class ApplicationDaemons
{
    private static IdentityHashMap<Thread, Thread> applicationdaemons = new IdentityHashMap<>();

    public synchronized void runDaemonsInSeperateThread() {
        new Runnable()
        {
            public void run()
            {
                runDaemons() ;
            }
        } ;    
    }

    private ApplicationDaemons() {}

    static synchronized void add(Thread hook) {
        if(applicationdaemons != null)
            applicationdaemons.put(hook, hook);
    }

    static synchronized boolean remove(Thread hook) {
        return applicationdaemons.remove(hook) != null;
    }

    static void runDaemons() {
        Collection<Thread> threads;
        synchronized(ApplicationDaemons.class) {
            threads = applicationdaemons.keySet();
            applicationdaemons = null;
        }

        for (Thread hook : threads) {
            hook.start();
        }
        for (Thread hook : threads) {
            try {
                hook.join();
            } catch (InterruptedException x) { }
        }
    }
}

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