org.apache.cassandra.utils.UUIDGen Maven / Gradle / Ivy
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* 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.cassandra.utils;
import java.net.InetAddress;
import java.nio.ByteBuffer;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Collection;
import java.util.Random;
import java.util.UUID;
import com.google.common.annotations.VisibleForTesting;
/**
* The goods are here: www.ietf.org/rfc/rfc4122.txt.
*/
public class UUIDGen
{
// A grand day! millis at 00:00:00.000 15 Oct 1582.
private static final long START_EPOCH = -12219292800000L;
private static final long clockSeqAndNode = makeClockSeqAndNode();
/*
* The min and max possible lsb for a UUID.
* Note that his is not 0 and all 1's because Cassandra TimeUUIDType
* compares the lsb parts as a signed byte array comparison. So the min
* value is 8 times -128 and the max is 8 times +127.
*
* Note that we ignore the uuid variant (namely, MIN_CLOCK_SEQ_AND_NODE
* have variant 2 as it should, but MAX_CLOCK_SEQ_AND_NODE have variant 0).
* I don't think that has any practical consequence and is more robust in
* case someone provides a UUID with a broken variant.
*/
private static final long MIN_CLOCK_SEQ_AND_NODE = 0x8080808080808080L;
private static final long MAX_CLOCK_SEQ_AND_NODE = 0x7f7f7f7f7f7f7f7fL;
// placement of this singleton is important. It needs to be instantiated *AFTER* the other statics.
private static final UUIDGen instance = new UUIDGen();
private long lastNanos;
private UUIDGen()
{
// make sure someone didn't whack the clockSeqAndNode by changing the order of instantiation.
if (clockSeqAndNode == 0) throw new RuntimeException("singleton instantiation is misplaced.");
}
/**
* Creates a type 1 UUID (time-based UUID).
*
* @return a UUID instance
*/
public static UUID getTimeUUID()
{
return new UUID(instance.createTimeSafe(), clockSeqAndNode);
}
/**
* Creates a type 1 UUID (time-based UUID) with the timestamp of @param when, in milliseconds.
*
* @return a UUID instance
*/
public static UUID getTimeUUID(long when)
{
return new UUID(createTime(fromUnixTimestamp(when)), clockSeqAndNode);
}
@VisibleForTesting
public static UUID getTimeUUID(long when, long clockSeqAndNode)
{
return new UUID(createTime(fromUnixTimestamp(when)), clockSeqAndNode);
}
/** creates a type 1 uuid from raw bytes. */
public static UUID getUUID(ByteBuffer raw)
{
return new UUID(raw.getLong(raw.position()), raw.getLong(raw.position() + 8));
}
/** decomposes a uuid into raw bytes. */
public static byte[] decompose(UUID uuid)
{
long most = uuid.getMostSignificantBits();
long least = uuid.getLeastSignificantBits();
byte[] b = new byte[16];
for (int i = 0; i < 8; i++)
{
b[i] = (byte)(most >>> ((7-i) * 8));
b[8+i] = (byte)(least >>> ((7-i) * 8));
}
return b;
}
/**
* Returns a 16 byte representation of a type 1 UUID (a time-based UUID),
* based on the current system time.
*
* @return a type 1 UUID represented as a byte[]
*/
public static byte[] getTimeUUIDBytes()
{
return createTimeUUIDBytes(instance.createTimeSafe());
}
/**
* Returns the smaller possible type 1 UUID having the provided timestamp.
*
* Warning: this method should only be used for querying as this
* doesn't at all guarantee the uniqueness of the resulting UUID.
*/
public static UUID minTimeUUID(long timestamp)
{
return new UUID(createTime(fromUnixTimestamp(timestamp)), MIN_CLOCK_SEQ_AND_NODE);
}
/**
* Returns the biggest possible type 1 UUID having the provided timestamp.
*
* Warning: this method should only be used for querying as this
* doesn't at all guarantee the uniqueness of the resulting UUID.
*/
public static UUID maxTimeUUID(long timestamp)
{
// unix timestamp are milliseconds precision, uuid timestamp are 100's
// nanoseconds precision. If we ask for the biggest uuid have unix
// timestamp 1ms, then we should not extend 100's nanoseconds
// precision by taking 10000, but rather 19999.
long uuidTstamp = fromUnixTimestamp(timestamp + 1) - 1;
return new UUID(createTime(uuidTstamp), MAX_CLOCK_SEQ_AND_NODE);
}
/**
* @param uuid
* @return milliseconds since Unix epoch
*/
public static long unixTimestamp(UUID uuid)
{
return (uuid.timestamp() / 10000) + START_EPOCH;
}
/**
* @param uuid
* @return microseconds since Unix epoch
*/
public static long microsTimestamp(UUID uuid)
{
return (uuid.timestamp() / 10) + START_EPOCH * 1000;
}
/**
* @param timestamp milliseconds since Unix epoch
* @return
*/
private static long fromUnixTimestamp(long timestamp) {
return (timestamp - START_EPOCH) * 10000;
}
/**
* Converts a milliseconds-since-epoch timestamp into the 16 byte representation
* of a type 1 UUID (a time-based UUID).
*
* Deprecated: This method goes again the principle of a time
* UUID and should not be used. For queries based on timestamp, minTimeUUID() and
* maxTimeUUID() can be used but this method has questionable usefulness. This is
* only kept because CQL2 uses it (see TimeUUID.fromStringCQL2) and we
* don't want to break compatibility.
*
* Warning: This method is not guaranteed to return unique UUIDs; Multiple
* invocations using identical timestamps will result in identical UUIDs.
*
* @param timeMillis
* @return a type 1 UUID represented as a byte[]
*/
public static byte[] getTimeUUIDBytes(long timeMillis)
{
return createTimeUUIDBytes(instance.createTimeUnsafe(timeMillis));
}
/**
* Converts a 100-nanoseconds precision timestamp into the 16 byte representation
* of a type 1 UUID (a time-based UUID).
*
* To specify a 100-nanoseconds precision timestamp, one should provide a milliseconds timestamp and
* a number 0 <= n < 10000 such that n*100 is the number of nanoseconds within that millisecond.
*
* Warning: This method is not guaranteed to return unique UUIDs; Multiple
* invocations using identical timestamps will result in identical UUIDs.
*
* @return a type 1 UUID represented as a byte[]
*/
public static byte[] getTimeUUIDBytes(long timeMillis, int nanos)
{
if (nanos >= 10000)
throw new IllegalArgumentException();
return createTimeUUIDBytes(instance.createTimeUnsafe(timeMillis, nanos));
}
private static byte[] createTimeUUIDBytes(long msb)
{
long lsb = clockSeqAndNode;
byte[] uuidBytes = new byte[16];
for (int i = 0; i < 8; i++)
uuidBytes[i] = (byte) (msb >>> 8 * (7 - i));
for (int i = 8; i < 16; i++)
uuidBytes[i] = (byte) (lsb >>> 8 * (7 - i));
return uuidBytes;
}
/**
* Returns a milliseconds-since-epoch value for a type-1 UUID.
*
* @param uuid a type-1 (time-based) UUID
* @return the number of milliseconds since the unix epoch
* @throws IllegalArgumentException if the UUID is not version 1
*/
public static long getAdjustedTimestamp(UUID uuid)
{
if (uuid.version() != 1)
throw new IllegalArgumentException("incompatible with uuid version: "+uuid.version());
return (uuid.timestamp() / 10000) + START_EPOCH;
}
private static long makeClockSeqAndNode()
{
long clock = new Random(System.currentTimeMillis()).nextLong();
long lsb = 0;
lsb |= 0x8000000000000000L; // variant (2 bits)
lsb |= (clock & 0x0000000000003FFFL) << 48; // clock sequence (14 bits)
lsb |= makeNode(); // 6 bytes
return lsb;
}
// needs to return two different values for the same when.
// we can generate at most 10k UUIDs per ms.
private synchronized long createTimeSafe()
{
long nanosSince = (System.currentTimeMillis() - START_EPOCH) * 10000;
if (nanosSince > lastNanos)
lastNanos = nanosSince;
else
nanosSince = ++lastNanos;
return createTime(nanosSince);
}
/** @param when time in milliseconds */
private long createTimeUnsafe(long when)
{
return createTimeUnsafe(when, 0);
}
private long createTimeUnsafe(long when, int nanos)
{
long nanosSince = ((when - START_EPOCH) * 10000) + nanos;
return createTime(nanosSince);
}
private static long createTime(long nanosSince)
{
long msb = 0L;
msb |= (0x00000000ffffffffL & nanosSince) << 32;
msb |= (0x0000ffff00000000L & nanosSince) >>> 16;
msb |= (0xffff000000000000L & nanosSince) >>> 48;
msb |= 0x0000000000001000L; // sets the version to 1.
return msb;
}
private static long makeNode()
{
/*
* We don't have access to the MAC address but need to generate a node part
* that identify this host as uniquely as possible.
* The spec says that one option is to take as many source that identify
* this node as possible and hash them together. That's what we do here by
* gathering all the ip of this host.
* Note that FBUtilities.getBroadcastAddress() should be enough to uniquely
* identify the node *in the cluster* but it triggers DatabaseDescriptor
* instanciation and the UUID generator is used in Stress for instance,
* where we don't want to require the yaml.
*/
Collection localAddresses = FBUtilities.getAllLocalAddresses();
if (localAddresses.isEmpty())
throw new RuntimeException("Cannot generate the node component of the UUID because cannot retrieve any IP addresses.");
// ideally, we'd use the MAC address, but java doesn't expose that.
byte[] hash = hash(localAddresses);
long node = 0;
for (int i = 0; i < Math.min(6, hash.length); i++)
node |= (0x00000000000000ff & (long)hash[i]) << (5-i)*8;
assert (0xff00000000000000L & node) == 0;
// Since we don't use the mac address, the spec says that multicast
// bit (least significant bit of the first octet of the node ID) must be 1.
return node | 0x0000010000000000L;
}
private static byte[] hash(Collection data)
{
try
{
MessageDigest messageDigest = MessageDigest.getInstance("MD5");
for(InetAddress addr : data)
messageDigest.update(addr.getAddress());
return messageDigest.digest();
}
catch (NoSuchAlgorithmException nsae)
{
throw new RuntimeException("MD5 digest algorithm is not available", nsae);
}
}
}
// for the curious, here is how I generated START_EPOCH
// Calendar c = Calendar.getInstance(TimeZone.getTimeZone("GMT-0"));
// c.set(Calendar.YEAR, 1582);
// c.set(Calendar.MONTH, Calendar.OCTOBER);
// c.set(Calendar.DAY_OF_MONTH, 15);
// c.set(Calendar.HOUR_OF_DAY, 0);
// c.set(Calendar.MINUTE, 0);
// c.set(Calendar.SECOND, 0);
// c.set(Calendar.MILLISECOND, 0);
// long START_EPOCH = c.getTimeInMillis();