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Elasticsearch subproject :server
/*
* Licensed to Elasticsearch under one or more contributor
* license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright
* ownership. Elasticsearch 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.elasticsearch.common;
import java.io.IOException;
import java.util.concurrent.atomic.AtomicInteger;
/** These are essentially flake ids (http://boundary.com/blog/2012/01/12/flake-a-decentralized-k-ordered-unique-id-generator-in-erlang) but
* we use 6 (not 8) bytes for timestamp, and use 3 (not 2) bytes for sequence number. */
class TimeBasedUUIDGenerator implements UUIDGenerator {
// We only use bottom 3 bytes for the sequence number. Paranoia: init with random int so that if JVM/OS/machine goes down, clock slips
// backwards, and JVM comes back up, we are less likely to be on the same sequenceNumber at the same time:
private final AtomicInteger sequenceNumber = new AtomicInteger(SecureRandomHolder.INSTANCE.nextInt());
// Used to ensure clock moves forward:
private long lastTimestamp;
private static final byte[] secureMungedAddress = MacAddressProvider.getSecureMungedAddress();
static {
assert secureMungedAddress.length == 6;
}
/** Puts the lower numberOfLongBytes from l into the array, starting index pos. */
private static void putLong(byte[] array, long l, int pos, int numberOfLongBytes) {
for (int i=0; i>> (i*8));
}
}
@Override
public String getBase64UUID() {
final int sequenceId = sequenceNumber.incrementAndGet() & 0xffffff;
long timestamp = System.currentTimeMillis();
synchronized (this) {
// Don't let timestamp go backwards, at least "on our watch" (while this JVM is running). We are still vulnerable if we are
// shut down, clock goes backwards, and we restart... for this we randomize the sequenceNumber on init to decrease chance of
// collision:
timestamp = Math.max(lastTimestamp, timestamp);
if (sequenceId == 0) {
// Always force the clock to increment whenever sequence number is 0, in case we have a long time-slip backwards:
timestamp++;
}
lastTimestamp = timestamp;
}
final byte[] uuidBytes = new byte[15];
// Only use lower 6 bytes of the timestamp (this will suffice beyond the year 10000):
putLong(uuidBytes, timestamp, 0, 6);
// MAC address adds 6 bytes:
System.arraycopy(secureMungedAddress, 0, uuidBytes, 6, secureMungedAddress.length);
// Sequence number adds 3 bytes:
putLong(uuidBytes, sequenceId, 12, 3);
assert 9 + secureMungedAddress.length == uuidBytes.length;
byte[] encoded;
try {
encoded = Base64.encodeBytesToBytes(uuidBytes, 0, uuidBytes.length, Base64.URL_SAFE);
} catch (IOException e) {
throw new IllegalStateException("should not be thrown", e);
}
// We are a multiple of 3 bytes so we should not see any padding:
assert encoded[encoded.length - 1] != '=';
return new String(encoded, 0, encoded.length, Base64.PREFERRED_ENCODING);
}
}