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Java client for Arcus memcached
There is a newer version: 1.14.0
/*
 * arcus-java-client : Arcus Java client
 * Copyright 2010-2014 NAVER Corp.
 *
 * Licensed 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 net.spy.memcached;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

import net.spy.memcached.compat.SpyObject;
import net.spy.memcached.util.ArcusKetamaNodeLocatorConfiguration;

public class ArcusKetamaNodeLocator extends SpyObject implements NodeLocator {

	TreeMap ketamaNodes;
	Collection allNodes;

	HashAlgorithm hashAlg;
	ArcusKetamaNodeLocatorConfiguration config;

	Lock lock = new ReentrantLock();

	public ArcusKetamaNodeLocator(List nodes, HashAlgorithm alg) {
		this(nodes, alg, new ArcusKetamaNodeLocatorConfiguration());
	}

	public ArcusKetamaNodeLocator(List nodes, HashAlgorithm alg,
			ArcusKetamaNodeLocatorConfiguration conf) {
		super();
		allNodes = nodes;
		hashAlg = alg;
		ketamaNodes = new TreeMap();
		config = conf;

		int numReps = config.getNodeRepetitions();
		for (MemcachedNode node : nodes) {
			// Ketama does some special work with md5 where it reuses chunks.
			if (alg == HashAlgorithm.KETAMA_HASH) {
				updateHash(node, false);
			} else {
				for (int i = 0; i < numReps; i++) {
					ketamaNodes.put(
							hashAlg.hash(config.getKeyForNode(node, i)), node);
				}
			}
		}
		assert ketamaNodes.size() == numReps * nodes.size();
	}

	private ArcusKetamaNodeLocator(TreeMap smn,
			Collection an, HashAlgorithm alg,
			ArcusKetamaNodeLocatorConfiguration conf) {
		super();
		ketamaNodes = smn;
		allNodes = an;
		hashAlg = alg;
		config = conf;
	}

	public Collection getAll() {
		return allNodes;
	}

	public MemcachedNode getPrimary(final String k) {
		MemcachedNode rv = getNodeForKey(hashAlg.hash(k));
		assert rv != null : "Found no node for key " + k;
		return rv;
	}

	long getMaxKey() {
		return ketamaNodes.lastKey();
	}

	MemcachedNode getNodeForKey(long hash) {
		MemcachedNode rv;

		lock.lock();
		try {
			if (!ketamaNodes.containsKey(hash)) {
				Long nodeHash = ketamaNodes.ceilingKey(hash);
				if (nodeHash == null) {
					hash = ketamaNodes.firstKey();
				} else {
					hash = nodeHash.longValue();
				}
				// Java 1.6 adds a ceilingKey method, but I'm still stuck in 1.5
				// in a lot of places, so I'm doing this myself.
				/*
				SortedMap tailMap = ketamaNodes.tailMap(hash);
				if (tailMap.isEmpty()) {
					hash = ketamaNodes.firstKey();
				} else {
					hash = tailMap.firstKey();
				}
				*/
			}
			rv = ketamaNodes.get(hash);
		} catch (RuntimeException e) {
			throw e;
		} finally {
			lock.unlock();
		}
		return rv;
	}

	public Iterator getSequence(String k) {
		return new KetamaIterator(k, allNodes.size());
	}

	public NodeLocator getReadonlyCopy() {
		TreeMap smn = new TreeMap(
				ketamaNodes);
		Collection an = new ArrayList(
				allNodes.size());

		lock.lock();
		try {
			// Rewrite the values a copy of the map.
			for (Map.Entry me : smn.entrySet()) {
				me.setValue(new MemcachedNodeROImpl(me.getValue()));
			}
			// Copy the allNodes collection.
			for (MemcachedNode n : allNodes) {
				an.add(new MemcachedNodeROImpl(n));
			}
		} catch (RuntimeException e) {
			throw e;
		} finally {
			lock.unlock();
		}

		return new ArcusKetamaNodeLocator(smn, an, hashAlg, config);
	}

	public void update(Collection toAttach,
			Collection toDelete) {
		lock.lock();
		try {
			// Add memcached nodes.
			for (MemcachedNode node : toAttach) {
				allNodes.add(node);
				updateHash(node, false);
			}

			// Remove memcached nodes.
			for (MemcachedNode node : toDelete) {
				allNodes.remove(node);
				updateHash(node, true);

				try {
					node.getSk().attach(null);
					node.shutdown();
				} catch (IOException e) {
					getLogger().error(
							"Failed to shutdown the node : " + node.toString());
					node.setSk(null);
				}
			}
		} catch (RuntimeException e) {
			throw e;
		} finally {
			lock.unlock();
		}
	}

	void updateHash(MemcachedNode node, boolean remove) {
		// Ketama does some special work with md5 where it reuses chunks.
		for (int i = 0; i < config.getNodeRepetitions() / 4; i++) {
			byte[] digest = HashAlgorithm.computeMd5(config.getKeyForNode(node,
					i));
			for (int h = 0; h < 4; h++) {
				Long k = ((long) (digest[3 + h * 4] & 0xFF) << 24)
						| ((long) (digest[2 + h * 4] & 0xFF) << 16)
						| ((long) (digest[1 + h * 4] & 0xFF) << 8)
						| (digest[h * 4] & 0xFF);
				if (remove) {
					ketamaNodes.remove(k);
					config.removeNode(node);
				} else {
					ketamaNodes.put(k, node);
				}
			}
		}
	}

	class KetamaIterator implements Iterator {

		final String key;
		long hashVal;
		int remainingTries;
		int numTries = 0;

		public KetamaIterator(final String k, final int t) {
			super();
			hashVal = hashAlg.hash(k);
			remainingTries = t;
			key = k;
		}

		private void nextHash() {
			long tmpKey = hashAlg.hash((numTries++) + key);
			// This echos the implementation of Long.hashCode()
			hashVal += (int) (tmpKey ^ (tmpKey >>> 32));
			hashVal &= 0xffffffffL; /* truncate to 32-bits */
			remainingTries--;
		}

		public boolean hasNext() {
			return remainingTries > 0;
		}

		public MemcachedNode next() {
			try {
				return getNodeForKey(hashVal);
			} finally {
				nextHash();
			}
		}

		public void remove() {
			throw new UnsupportedOperationException("remove not supported");
		}

	}
}