Java tutorial
/* * 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.cassandra.utils; import java.net.InetAddress; import java.net.NetworkInterface; import java.net.SocketException; import java.nio.ByteBuffer; import java.security.SecureRandom; import java.util.Collection; import java.util.Collections; import java.util.Enumeration; import java.util.HashSet; import java.util.List; import java.util.Random; import java.util.Set; import java.util.UUID; import java.util.concurrent.atomic.AtomicLong; import java.util.concurrent.TimeUnit; import java.util.function.Function; import java.util.stream.Collectors; import com.google.common.annotations.VisibleForTesting; import com.google.common.hash.Hasher; import com.google.common.hash.Hashing; import com.google.common.primitives.Ints; import org.apache.cassandra.config.DatabaseDescriptor; import org.apache.cassandra.locator.InetAddressAndPort; /** * 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(); public static final int UUID_LEN = 16; /* * 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; private static final SecureRandom secureRandom = new SecureRandom(); // placement of this singleton is important. It needs to be instantiated *AFTER* the other statics. private static final UUIDGen instance = new UUIDGen(); private AtomicLong lastNanos = new AtomicLong(); 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); } /** * Returns a version 1 UUID using the provided timestamp and the local clock and sequence. * <p> * Note that this method is generally only safe to use if you can guarantee that the provided * parameter is unique across calls (otherwise the returned UUID won't be unique accross calls). * * @param whenInMicros a unix time in microseconds. * @return a new UUID {@code id} such that {@code microsTimestamp(id) == whenInMicros}. Please not that * multiple calls to this method with the same value of {@code whenInMicros} will return the <b>same</b> * UUID. */ public static UUID getTimeUUIDFromMicros(long whenInMicros) { long whenInMillis = whenInMicros / 1000; long nanos = (whenInMicros - (whenInMillis * 1000)) * 10; return getTimeUUID(whenInMillis, nanos); } /** * Similar to {@link #getTimeUUIDFromMicros}, but randomize (using SecureRandom) the clock and sequence. * <p> * If you can guarantee that the {@code whenInMicros} argument is unique (for this JVM instance) for * every call, then you should prefer {@link #getTimeUUIDFromMicros} which is faster. If you can't * guarantee this however, this method will ensure the returned UUID are still unique (accross calls) * through randomization. * * @param whenInMicros a unix time in microseconds. * @return a new UUID {@code id} such that {@code microsTimestamp(id) == whenInMicros}. The UUID returned * by different calls will be unique even if {@code whenInMicros} is not. */ public static UUID getRandomTimeUUIDFromMicros(long whenInMicros) { long whenInMillis = whenInMicros / 1000; long nanos = (whenInMicros - (whenInMillis * 1000)) * 10; return new UUID(createTime(fromUnixTimestamp(whenInMillis, nanos)), secureRandom.nextLong()); } public static UUID getTimeUUID(long when, long nanos) { return new UUID(createTime(fromUnixTimestamp(when, nanos)), clockSeqAndNode); } @VisibleForTesting public static UUID getTimeUUID(long when, long nanos, long clockSeqAndNode) { return new UUID(createTime(fromUnixTimestamp(when, nanos)), 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)); } public static ByteBuffer toByteBuffer(UUID uuid) { ByteBuffer buffer = ByteBuffer.allocate(UUID_LEN); buffer.putLong(uuid.getMostSignificantBits()); buffer.putLong(uuid.getLeastSignificantBits()); buffer.flip(); return buffer; } /** 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. * * <b>Warning:</b> 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. * * <b>Warning:</b> 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 seconds since Unix epoch */ public static int unixTimestampInSec(UUID uuid) { return Ints.checkedCast(TimeUnit.MILLISECONDS.toSeconds(unixTimestamp(uuid))); } /** * @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 fromUnixTimestamp(timestamp, 0L); } private static long fromUnixTimestamp(long timestamp, long nanos) { return ((timestamp - START_EPOCH) * 10000) + nanos; } /** * 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 {@code 0 <= n < 10000} such that n*100 is the number of nanoseconds within that millisecond. * * <p><i><b>Warning:</b> This method is not guaranteed to return unique UUIDs; Multiple * invocations using identical timestamps will result in identical UUIDs.</i></p> * * @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 SecureRandom().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 long createTimeSafe() { long newLastNanos; while (true) { //Generate a candidate value for new lastNanos newLastNanos = (System.currentTimeMillis() - START_EPOCH) * 10000; long originalLastNanos = lastNanos.get(); if (newLastNanos > originalLastNanos) { //Slow path once per millisecond do a CAS if (lastNanos.compareAndSet(originalLastNanos, newLastNanos)) { break; } } else { //Fast path do an atomic increment //Or when falling behind this will move time forward past the clock if necessary newLastNanos = lastNanos.incrementAndGet(); break; } } return createTime(newLastNanos); } 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.getJustBroadcastAddress() 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<InetAddressAndPort> localAddresses = 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<InetAddressAndPort> data) { // Identify the host. Hasher hasher = Hashing.md5().newHasher(); for (InetAddressAndPort addr : data) { hasher.putBytes(addr.addressBytes); hasher.putInt(addr.port); } // Identify the process on the load: we use both the PID and class loader hash. long pid = NativeLibrary.getProcessID(); if (pid < 0) pid = new Random(System.currentTimeMillis()).nextLong(); HashingUtils.updateWithLong(hasher, pid); ClassLoader loader = UUIDGen.class.getClassLoader(); int loaderId = loader != null ? System.identityHashCode(loader) : 0; HashingUtils.updateWithInt(hasher, loaderId); return hasher.hash().asBytes(); } /** * Helper function used exclusively by UUIDGen to create **/ public static Collection<InetAddressAndPort> getAllLocalAddresses() { Set<InetAddressAndPort> localAddresses = new HashSet<>(); try { Enumeration<NetworkInterface> nets = NetworkInterface.getNetworkInterfaces(); if (nets != null) { while (nets.hasMoreElements()) { Function<InetAddress, InetAddressAndPort> converter = address -> InetAddressAndPort .getByAddressOverrideDefaults(address, 0); List<InetAddressAndPort> addresses = Collections.list(nets.nextElement().getInetAddresses()) .stream().map(converter).collect(Collectors.toList()); localAddresses.addAll(addresses); } } } catch (SocketException e) { throw new AssertionError(e); } if (DatabaseDescriptor.isDaemonInitialized()) { localAddresses.add(FBUtilities.getBroadcastAddressAndPort()); localAddresses.add(FBUtilities.getBroadcastNativeAddressAndPort()); localAddresses.add(FBUtilities.getLocalAddressAndPort()); } return localAddresses; } } // 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();