/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package org.apache.commons.collections;

import java.util.AbstractCollection;
import java.util.AbstractSet;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;

A StaticBucketMap is an efficient, thread-safe implementation of
java.util.Map that performs well in in a highly thread-contentious environment. The map supports very efficient get, put, remove and containsKey operations, assuming (approximate) uniform hashing and that the number of entries does not exceed the number of buckets. If the number of entries exceeds the number of buckets or if the hash codes of the objects are not uniformly distributed, these operations have a worst case scenario that is proportional to the number of elements in the map (O(n)).
 Each bucket in the hash table has its own monitor, so two threads can safely operate on the map at the same time, often without incurring any monitor contention. This means that you don't have to wrap instances of this class with Collections.synchronizedMap(Map<Object,Object>); instances are already thread-safe. Unfortunately, however, this means that this map implementation behaves in ways you may find disconcerting. Bulk operations, such as putAll or the retainAll operation in collection views, are not atomic.  If two threads are simultaneously 
executing 
  staticBucketMapInstance.putAll(map);

and
  staticBucketMapInstance.entrySet().removeAll(map.entrySet());

then the results are generally random.  Those two statement could cancel
each other out, leaving staticBucketMapInstance essentially 
unchanged, or they could leave some random subset of map in 
staticBucketMapInstance.
 Also, much like an encyclopedia, the results of size() and isEmpty() are out-of-date as soon as they are produced.

The iterators returned by the collection views of this class are not
fail-fast.  They will never raise a ConcurrentModificationException. Keys and values added to the map after the iterator is created do not necessarily appear during iteration. Similarly, the iterator does not necessarily fail to return keys and values that were removed after the iterator was created.
 Finally, unlike HashMap-style implementations, this class never rehashes the map.  The number of buckets is fixed 
at construction time and never altered.  Performance may degrade if 
you do not allocate enough buckets upfront.
 The atomic(Runnable) method is provided to allow atomic iterations and bulk operations; however, overuse of atomic will basically result in a map that's slower than an ordinary synchronized HashMap. Use this class if you do not require reliable bulk operations and iterations, or if you can make your own guarantees about how bulk operations will affect the map.

Author:
Berin Loritsch, Gerhard Froehlich, Michael A. Smith, Paul Jack, Leo Sutic, Janek Bogucki, Kazuya Ujihara
Deprecated:
Moved to map subpackage. Due to be removed in v4.0.
Since:
Commons Collections 2.1
Version:
$Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $/**
 * A StaticBucketMap is an efficient, thread-safe implementation of
 * <code>java.util.Map</code> that performs well in in a highly
 * thread-contentious environment.  The map supports very efficient
 * {@link #get(Object) get}, {@link #put(Object,Object) put}, 
 * {@link #remove(Object) remove} and {@link #containsKey(Object) containsKey}
 * operations, assuming (approximate) uniform hashing and
 * that the number of entries does not exceed the number of buckets.  If the
 * number of entries exceeds the number of buckets or if the hash codes of the
 * objects are not uniformly distributed, these operations have a worst case
 * scenario that is proportional to the number of elements in the map
 * (<i>O(n)</i>).<p>
 *
 * Each bucket in the hash table has its own monitor, so two threads can 
 * safely operate on the map at the same time, often without incurring any 
 * monitor contention.  This means that you don't have to wrap instances
 * of this class with {@link java.util.Collections#synchronizedMap(Map)};
 * instances are already thread-safe.  Unfortunately, however, this means 
 * that this map implementation behaves in ways you may find disconcerting.  
 * Bulk operations, such as {@link #putAll(Map) putAll} or the
 * {@link Collection#retainAll(Collection) retainAll} operation in collection 
 * views, are <i>not</i> atomic.  If two threads are simultaneously 
 * executing 
 *
 * <pre>
 *   staticBucketMapInstance.putAll(map);
 * </pre>
 *
 * and
 *
 * <pre>
 *   staticBucketMapInstance.entrySet().removeAll(map.entrySet());
 * </pre>
 *
 * then the results are generally random.  Those two statement could cancel
 * each other out, leaving <code>staticBucketMapInstance</code> essentially 
 * unchanged, or they could leave some random subset of <code>map</code> in 
 * <code>staticBucketMapInstance</code>.<p>
 *
 * Also, much like an encyclopedia, the results of {@link #size()} and 
 * {@link #isEmpty()} are out-of-date as soon as they are produced.<p>
 *
 * The iterators returned by the collection views of this class are <i>not</i>
 * fail-fast.  They will <i>never</i> raise a 
 * {@link java.util.ConcurrentModificationException}.  Keys and values 
 * added to the map after the iterator is created do not necessarily appear
 * during iteration.  Similarly, the iterator does not necessarily fail to 
 * return keys and values that were removed after the iterator was created.<p>
 *
 * Finally, unlike {@link java.util.HashMap}-style implementations, this
 * class <i>never</i> rehashes the map.  The number of buckets is fixed 
 * at construction time and never altered.  Performance may degrade if 
 * you do not allocate enough buckets upfront.<p>
 *
 * The {@link #atomic(Runnable)} method is provided to allow atomic iterations
 * and bulk operations; however, overuse of {@link #atomic(Runnable) atomic}
 * will basically result in a map that's slower than an ordinary synchronized
 * {@link java.util.HashMap}.
 *
 * Use this class if you do not require reliable bulk operations and 
 * iterations, or if you can make your own guarantees about how bulk 
 * operations will affect the map.<p>
 *
 * @deprecated Moved to map subpackage. Due to be removed in v4.0.
 * @since Commons Collections 2.1
 * @version $Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $
 * 
 * @author <a href="mailto:bloritsch@apache.org">Berin Loritsch</a>
 * @author <a href="mailto:g-froehlich@gmx.de">Gerhard Froehlich</a>
 * @author <a href="mailto:mas@apache.org">Michael A. Smith</a>
 * @author Paul Jack
 * @author Leo Sutic
 * @author Janek Bogucki
 * @author Kazuya Ujihara
 */
public final class StaticBucketMap implements Map {

    private static final int DEFAULT_BUCKETS = 255;
    private Node[] m_buckets;
    private Lock[] m_locks;

    
Initializes the map with the default number of buckets (255).
/**
     * Initializes the map with the default number of buckets (255).
     */
    public StaticBucketMap()
    {
        this( DEFAULT_BUCKETS );
    }

    
Initializes the map with a specified number of buckets.  The number
of buckets is never below 17, and is always an odd number (StaticBucketMap
ensures this). The number of buckets is inversely proportional to the
chances for thread contention.  The fewer buckets, the more chances for
thread contention.  The more buckets the fewer chances for thread
contention.
Params:
numBuckets –  the number of buckets for this map/**
     * Initializes the map with a specified number of buckets.  The number
     * of buckets is never below 17, and is always an odd number (StaticBucketMap
     * ensures this). The number of buckets is inversely proportional to the
     * chances for thread contention.  The fewer buckets, the more chances for
     * thread contention.  The more buckets the fewer chances for thread
     * contention.
     *
     * @param numBuckets  the number of buckets for this map
     */
    public StaticBucketMap( int numBuckets )
    {
        int size = Math.max( 17, numBuckets );

        // Ensure that bucketSize is never a power of 2 (to ensure maximal distribution)
        if( size % 2 == 0 )
        {
            size--;
        }

        m_buckets = new Node[ size ];
        m_locks = new Lock[ size ];

        for( int i = 0; i < size; i++ )
        {
            m_locks[ i ] = new Lock();
        }
    }

    
Determine the exact hash entry for the key.  The hash algorithm
is rather simplistic, but it does the job:
  He = |Hk mod n|


  He is the entry's hashCode, Hk is the key's hashCode, and n is
  the number of buckets.

/**
     * Determine the exact hash entry for the key.  The hash algorithm
     * is rather simplistic, but it does the job:
     *
     * <pre>
     *   He = |Hk mod n|
     * </pre>
     *
     * <p>
     *   He is the entry's hashCode, Hk is the key's hashCode, and n is
     *   the number of buckets.
     * </p>
     */
    private final int getHash( Object key )
    {
        if( key == null ) return 0;
        int hash = key.hashCode();
        hash += ~(hash << 15);
        hash ^= (hash >>> 10);
        hash += (hash << 3);
        hash ^= (hash >>> 6);
        hash += ~(hash << 11);
        hash ^= (hash >>> 16);
        hash %= m_buckets.length;
        return ( hash < 0 ) ? hash * -1 : hash;
    }

    
 Implements Map.keySet(). /**
     *  Implements {@link Map#keySet()}.
     */
    public Set keySet()
    {
        return new KeySet();
    }

    
 Implements Map.size(). /**
     *  Implements {@link Map#size()}.
     */
    public int size()
    {
        int cnt = 0;

        for( int i = 0; i < m_buckets.length; i++ )
        {
            cnt += m_locks[i].size;
        }

        return cnt;
    }

    
 Implements Map.put(Object, Object). /**
     *  Implements {@link Map#put(Object, Object)}.
     */
    public Object put( final Object key, final Object value )
    {
        int hash = getHash( key );

        synchronized( m_locks[ hash ] )
        {
            Node n = m_buckets[ hash ];

            if( n == null )
            {
                n = new Node();
                n.key = key;
                n.value = value;
                m_buckets[ hash ] = n;
                m_locks[hash].size++;
                return null;
            }

            // Set n to the last node in the linked list.  Check each key along the way
            //  If the key is found, then change the value of that node and return
            //  the old value.
            for( Node next = n; next != null; next = next.next )
            {
                n = next;

                if( n.key == key || ( n.key != null && n.key.equals( key ) ) )
                {
                    Object returnVal = n.value;
                    n.value = value;
                    return returnVal;
                }
            }

            // The key was not found in the current list of nodes, add it to the end
            //  in a new node.
            Node newNode = new Node();
            newNode.key = key;
            newNode.value = value;
            n.next = newNode;
            m_locks[hash].size++;
        }

        return null;
    }

    
 Implements Map.get(Object). /**
     *  Implements {@link Map#get(Object)}.
     */
    public Object get( final Object key )
    {
        int hash = getHash( key );

        synchronized( m_locks[ hash ] )
        {
            Node n = m_buckets[ hash ];

            while( n != null )
            {
                if( n.key == key || ( n.key != null && n.key.equals( key ) ) )
                {
                    return n.value;
                }

                n = n.next;
            }
        }

        return null;
    }

    
Implements Map.containsKey(Object). /**
     * Implements {@link Map#containsKey(Object)}.
     */
    public boolean containsKey( final Object key )
    {
        int hash = getHash( key );

        synchronized( m_locks[ hash ] )
        {
            Node n = m_buckets[ hash ];

            while( n != null )
            {
                if( n.key == key || ( n.key != null && n.key.equals( key ) ) )
                {
                    return true;
                }

                n = n.next;
            }
        }

        return false;
    }

    
Implements Map.containsValue(Object). /**
     * Implements {@link Map#containsValue(Object)}.
     */
    public boolean containsValue( final Object value )
    {
        for( int i = 0; i < m_buckets.length; i++ )
        {
            synchronized( m_locks[ i ] )
            {
                Node n = m_buckets[ i ];

                while( n != null )
                {
                    if( n.value == value || 
                        (n.value != null && n.value.equals( value ) ) )
                    {
                        return true;
                    }

                    n = n.next;
                }
            }
        }

        return false;
    }

    
 Implements Map.values(). /**
     *  Implements {@link Map#values()}.
     */
    public Collection values()
    {
        return new Values();
    }

    
 Implements Map.entrySet(). /**
     *  Implements {@link Map#entrySet()}.
     */
    public Set entrySet()
    {
        return new EntrySet();
    }

    
 Implements Map.putAll(Map). /**
     *  Implements {@link Map#putAll(Map)}.
     */
    public void putAll( Map other )
    {
        Iterator i = other.keySet().iterator();

        while( i.hasNext() )
        {
            Object key = i.next();
            put( key, other.get( key ) );
        }
    }

    
 Implements Map.remove(Object). /**
     *  Implements {@link Map#remove(Object)}.
     */
    public Object remove( Object key )
    {
        int hash = getHash( key );

        synchronized( m_locks[ hash ] )
        {
            Node n = m_buckets[ hash ];
            Node prev = null;

            while( n != null )
            {
                if( n.key == key || ( n.key != null && n.key.equals( key ) ) )
                {
                    // Remove this node from the linked list of nodes.
                    if( null == prev )
                    {
                        // This node was the head, set the next node to be the new head.
                        m_buckets[ hash ] = n.next;
                    }
                    else
                    {
                        // Set the next node of the previous node to be the node after this one.
                        prev.next = n.next;
                    }
                    m_locks[hash].size--;
                    return n.value;
                }

                prev = n;
                n = n.next;
            }
        }

        return null;
    }

    
 Implements Map.isEmpty(). /**
     *  Implements {@link Map#isEmpty()}.
     */
    public final boolean isEmpty()
    {
        return size() == 0;
    }

    
 Implements Map.clear(). /**
     *  Implements {@link Map#clear()}.
     */
    public final void clear()
    {
        for( int i = 0; i < m_buckets.length; i++ )
        {
            Lock lock = m_locks[i];
            synchronized (lock) {
                m_buckets[ i ] = null;
                lock.size = 0;
            }
        }
    }

    
 Implements Map.equals(Object). /**
     *  Implements {@link Map#equals(Object)}.
     */
    public final boolean equals( Object obj )
    {
        if( obj == null ) return false;
        if( obj == this ) return true;

        if( !( obj instanceof Map ) ) return false;

        Map other = (Map)obj;
        
        return entrySet().equals(other.entrySet());
    }

    
 Implements Map.hashCode(). /**
     *  Implements {@link Map#hashCode()}.
     */
    public final int hashCode() 
    {
        int hashCode = 0;

        for( int i = 0; i < m_buckets.length; i++ )
        {
            synchronized( m_locks[ i ] )
            {
                Node n = m_buckets[ i ];

                while( n != null )
                {
                    hashCode += n.hashCode();
                    n = n.next;
                }
            }
        }
        return hashCode;
    }

    
The Map.Entry for the StaticBucketMap.
/**
     * The Map.Entry for the StaticBucketMap.
     */
    private static final class Node implements Map.Entry, KeyValue
    {
        protected Object key;
        protected Object value;
        protected Node next;

        public Object getKey()
        {
            return key;
        }

        public Object getValue()
        {
            return value;
        }

        public int hashCode()
        {
            return ( ( key == null ? 0 : key.hashCode() ) ^
                     ( value == null ? 0 : value.hashCode() ) ); 
        }

        public boolean equals(Object o) {
            if( o == null ) return false;
            if( o == this ) return true;        
            
            if ( ! (o instanceof Map.Entry ) )
                return false;

            Map.Entry e2 = (Map.Entry)o;

            return ((key == null ?
                     e2.getKey() == null : key.equals(e2.getKey())) &&
                    (value == null ?
                     e2.getValue() == null : value.equals(e2.getValue())));
        }

        public Object setValue( Object val )
        {
            Object retVal = value;
            value = val;
            return retVal;
        }
    }

    private final static class Lock {

        public int size;

    }


    private class EntryIterator implements Iterator {

        private ArrayList current = new ArrayList();
        private int bucket;
        private Map.Entry last;


        public boolean hasNext() {
            if (current.size() > 0) return true;
            while (bucket < m_buckets.length) {
                synchronized (m_locks[bucket]) {
                    Node n = m_buckets[bucket];
                    while (n != null) {
                        current.add(n);
                        n = n.next;
                    }
                    bucket++;
                    if (current.size() > 0) return true;
                }
            }
            return false;
        }

        protected Map.Entry nextEntry() {
            if (!hasNext()) throw new NoSuchElementException();
            last = (Map.Entry)current.remove(current.size() - 1);
            return last;
        }

        public Object next() {
            return nextEntry();
        }

        public void remove() {
            if (last == null) throw new IllegalStateException();
            StaticBucketMap.this.remove(last.getKey());
            last = null;
        }

    }

    private class ValueIterator extends EntryIterator {

        public Object next() {
            return nextEntry().getValue();
        }

    }

    private class KeyIterator extends EntryIterator {

        public Object next() {
            return nextEntry().getKey();
        }

    }

    private class EntrySet extends AbstractSet {

        public int size() {
            return StaticBucketMap.this.size();
        }

        public void clear() {
            StaticBucketMap.this.clear();
        }

        public Iterator iterator() {
            return new EntryIterator();
        }

        public boolean contains(Object o) {
            Map.Entry entry = (Map.Entry)o;
            int hash = getHash(entry.getKey());
            synchronized (m_locks[hash]) {
                for (Node n = m_buckets[hash]; n != null; n = n.next) {
                    if (n.equals(entry)) return true;
                }
            }
            return false;
        }

        public boolean remove(Object obj) {
            if (obj instanceof Map.Entry == false) {
                return false;
            }
            Map.Entry entry = (Map.Entry) obj;
            int hash = getHash(entry.getKey());
            synchronized (m_locks[hash]) {
                for (Node n = m_buckets[hash]; n != null; n = n.next) {
                    if (n.equals(entry)) {
                        StaticBucketMap.this.remove(n.getKey());
                        return true;
                    }
                }
            }
            return false;
        }

    }


    private class KeySet extends AbstractSet {

        public int size() {
            return StaticBucketMap.this.size();
        }

        public void clear() {
            StaticBucketMap.this.clear();
        }

        public Iterator iterator() {
            return new KeyIterator();
        }

        public boolean contains(Object o) {
            return StaticBucketMap.this.containsKey(o);
        }

        public boolean remove(Object o) {
            int hash = getHash(o);
            synchronized (m_locks[hash]) {
                for (Node n = m_buckets[hash]; n != null; n = n.next) {
                    Object k = n.getKey();
                    if ((k == o) || ((k != null) && k.equals(o))) {
                        StaticBucketMap.this.remove(k);
                        return true;
                    }
                }
            }
            return false;

        }

    }


    private class Values extends AbstractCollection {

        public int size() {
            return StaticBucketMap.this.size();
        }

        public void clear() {
            StaticBucketMap.this.clear();
        }

        public Iterator iterator() {
            return new ValueIterator();
        }

    }


    
 Prevents any operations from occurring on this map while the given Runnable executes. This method can be used, for instance, to execute a bulk operation atomically: 
   staticBucketMapInstance.atomic(new Runnable() {
       public void run() {
           staticBucketMapInstance.putAll(map);
       }
   });
 
 It can also be used if you need a reliable iterator:
 
   staticBucketMapInstance.atomic(new Runnable() {
       public void run() {
           Iterator iterator = staticBucketMapInstance.iterator();
           while (iterator.hasNext()) {
               foo(iterator.next();
           }
       }
   });
 
 Implementation note: This method requires a lot of time
 and a ton of stack space.  Essentially a recursive algorithm is used
 to enter each bucket's monitor.  If you have twenty thousand buckets
 in your map, then the recursive method will be invoked twenty thousand
 times.  You have been warned.
 @param r  the code to execute atomically
/**
     *  Prevents any operations from occurring on this map while the
     *  given {@link Runnable} executes.  This method can be used, for
     *  instance, to execute a bulk operation atomically: 
     *
     *  <pre>
     *    staticBucketMapInstance.atomic(new Runnable() {
     *        public void run() {
     *            staticBucketMapInstance.putAll(map);
     *        }
     *    });
     *  </pre>
     *
     *  It can also be used if you need a reliable iterator:
     *
     *  <pre>
     *    staticBucketMapInstance.atomic(new Runnable() {
     *        public void run() {
     *            Iterator iterator = staticBucketMapInstance.iterator();
     *            while (iterator.hasNext()) {
     *                foo(iterator.next();
     *            }
     *        }
     *    });
     *  </pre>
     *
     *  <B>Implementation note:</B> This method requires a lot of time
     *  and a ton of stack space.  Essentially a recursive algorithm is used
     *  to enter each bucket's monitor.  If you have twenty thousand buckets
     *  in your map, then the recursive method will be invoked twenty thousand
     *  times.  You have been warned.
     *
     *  @param r  the code to execute atomically
     */
    public void atomic(Runnable r) {
        if (r == null) throw new NullPointerException();
        atomic(r, 0);
    }

    private void atomic(Runnable r, int bucket) {
        if (bucket >= m_buckets.length) {
            r.run();
            return;
        }
        synchronized (m_locks[bucket]) {
            atomic(r, bucket + 1);
        }
    }


}