org.glassfish.grizzly.memcached.ConsistentHashStore Maven / Gradle / Ivy
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package org.glassfish.grizzly.memcached;
import org.glassfish.grizzly.Grizzly;
import org.glassfish.grizzly.utils.DataStructures;
import java.nio.ByteBuffer;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Collections;
import java.util.Set;
import java.util.concurrent.ConcurrentSkipListMap;
import java.util.logging.Level;
import java.util.logging.Logger;
import java.util.zip.CRC32;
/**
* The implementation class of the Consistent Hashing algorithms
*
* Given keys and values will be hashed by MD5 and stored in sorted map.
* If MD5 is not supported, CRC32 will be used.
* Values(such as server list) can be added and removed dynamically.
*
* This store supports keys of String, byte array and ByteBuffer type
*
* Ketama's logic applied partially.
*
* This class should be thread-safe.
*
* Example of use:
* See org.glassfish.grizzly.memcached.ConsistentHashStoreTest's test codes
*
* @author Bongjae Chang
*/
public class ConsistentHashStore {
private static final Logger logger = Grizzly.logger(ConsistentHashStore.class);
private static final ThreadLocal md5ThreadLocal = new ThreadLocal();
private volatile static boolean md5NotSupported;
private static final int REPLICA_NUMBER = 160;
private final ConcurrentSkipListMap buckets = new ConcurrentSkipListMap();
private final Set values = Collections.newSetFromMap(DataStructures.getConcurrentMap());
/**
* Add the value such as a server name
*
* @param value value to be added
*/
public void add(final T value) {
addOrRemove(value, true);
values.add(value);
}
/**
* Remove the value which already added by {@link #add}
*
* @param value value to be removed in this store
*/
public void remove(final T value) {
addOrRemove(value, false);
values.remove(value);
}
/**
* Check if this store has {@code value}
*
* @param value value to be checked
* @return true if this store already contains {@code value}
*/
public boolean hasValue(final T value) {
return value != null && values.contains(value);
}
/**
* Clear all values and keys
*/
public void clear() {
buckets.clear();
values.clear();
}
private void addOrRemove(final T value, boolean add) {
if (value == null) {
return;
}
final MessageDigest md5 = getMessageDigest();
if (md5 == null) {
for (int i = 0; i < REPLICA_NUMBER; i++) {
final StringBuilder stringBuilder = new StringBuilder(64);
stringBuilder.append(value).append('-').append(i);
CRC32 crc32 = new CRC32();
crc32.update(stringBuilder.toString().getBytes());
long hashKey = crc32.getValue() >> 16 & 0x7fff;
if (add) {
buckets.putIfAbsent(hashKey, value);
if (logger.isLoggable(Level.FINE)) {
logger.log(Level.FINE, "added {0} to the bucket successfully. key={1}", new Object[]{value, hashKey});
}
} else {
buckets.remove(hashKey);
if (logger.isLoggable(Level.FINE)) {
logger.log(Level.FINE, "removed {0} to the bucket successfully. key={1}", new Object[]{value, hashKey});
}
}
}
} else {
for (int i = 0; i < REPLICA_NUMBER / 4; i++) {
final StringBuilder stringBuilder = new StringBuilder(64);
stringBuilder.append(value).append('-').append(i);
byte[] digest = md5.digest(stringBuilder.toString().getBytes());
for (int j = 0; j < 4; j++) {
long hashKey = ((long) (digest[3 + j * 4] & 0xFF) << 24)
| ((long) (digest[2 + j * 4] & 0xFF) << 16)
| ((long) (digest[1 + j * 4] & 0xFF) << 8)
| ((long) (digest[j * 4] & 0xFF));
if (add) {
buckets.putIfAbsent(hashKey, value);
if (logger.isLoggable(Level.FINE)) {
logger.log(Level.FINE, "added {0} to the bucket successfully. key={1}", new Object[]{value, hashKey});
}
} else {
buckets.remove(hashKey);
if (logger.isLoggable(Level.FINE)) {
logger.log(Level.FINE, "removed {0} to the bucket successfully. key={1}", new Object[]{value, hashKey});
}
}
}
}
}
}
/**
* Get the value corresponding to the given key
*
* @param key String key
* @return the selected value corresponding to the {@code key}
*/
public T get(final String key) {
if (key == null) {
return null;
}
return get(key.getBytes());
}
/**
* Get the value corresponding to the given key
*
* @param key byte array key
* @return the selected value corresponding to the {@code key}
*/
public T get(final byte[] key) {
if (key == null) {
return null;
}
if (buckets.size() == 0) {
return null;
}
if (buckets.size() == 1) {
return buckets.firstEntry().getValue();
}
// ceilingKey returns the least key greater than or equal to the given key,
// or null if no such key.
Long hashKey = buckets.ceilingKey(calculateHash(key));
// if none found, it must be at the end, return the lowest in the tree
// (we go over the end the continuum to the first entry)
if (hashKey == null) {
hashKey = buckets.firstKey();
}
return buckets.get(hashKey);
}
/**
* Get the value corresponding to the given key
*
* @param key {@link ByteBuffer} key
* @return the selected value corresponding to the {@code key}
*/
public T get(final ByteBuffer key) {
if (key == null) {
return null;
}
if (buckets.size() == 0) {
return null;
}
if (buckets.size() == 1) {
return buckets.firstEntry().getValue();
}
// ceilingKey returns the least key greater than or equal to the given key,
// or null if no such key.
Long hashKey = buckets.ceilingKey(calculateHash(key));
// if none found, it must be at the end, return the lowest in the tree
// (we go over the end the continuum to the first entry)
if (hashKey == null) {
hashKey = buckets.firstKey();
}
return buckets.get(hashKey);
}
private long calculateHash(final byte[] key) {
if (key == null) {
return 0;
}
final long hash;
final MessageDigest md5 = getMessageDigest();
if (md5 == null) {
CRC32 crc32 = new CRC32();
crc32.update(key);
hash = crc32.getValue() >> 16 & 0x7fff;
} else {
md5.reset();
final byte[] digest = md5.digest(key);
hash = ((long) (digest[3] & 0xFF) << 24) | ((long) (digest[2] & 0xFF) << 16) | ((long) (digest[1] & 0xFF) << 8) | (long) (digest[0] & 0xFF);
}
return hash;
}
private long calculateHash(final ByteBuffer key) {
if (key == null) {
return 0;
}
final long hash;
final MessageDigest md5 = getMessageDigest();
if (md5 == null) {
if (key.hasArray()) {
CRC32 crc32 = new CRC32();
byte[] b = key.array();
int ofs = key.arrayOffset();
int pos = key.position();
int lim = key.limit();
crc32.update(b, ofs + pos, lim - pos);
key.position(lim);
hash = crc32.getValue() >> 16 & 0x7fff;
} else {
hash = key.hashCode();
}
} else {
md5.reset();
md5.update(key);
final byte[] digest = md5.digest();
hash = ((long) (digest[3] & 0xFF) << 24) | ((long) (digest[2] & 0xFF) << 16) | ((long) (digest[1] & 0xFF) << 8) | (long) (digest[0] & 0xFF);
}
return hash;
}
private static MessageDigest getMessageDigest() {
if (md5NotSupported) {
return null;
}
MessageDigest md5 = md5ThreadLocal.get();
if (md5 == null) {
try {
md5 = MessageDigest.getInstance("MD5");
md5ThreadLocal.set(md5);
} catch (NoSuchAlgorithmException nsae) {
md5NotSupported = true;
if (logger.isLoggable(Level.WARNING)) {
logger.log(Level.WARNING, "failed to get the md5", nsae);
}
}
}
return md5;
}
}
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