com.github.benmanes.caffeine.cache.tracing.TracerIdGenerator Maven / Gradle / Ivy
/*
* Copyright 2015 Ben Manes. All Rights Reserved.
*
* 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 com.github.benmanes.caffeine.cache.tracing;
import java.net.InetAddress;
import java.net.NetworkInterface;
import java.net.SocketException;
import java.net.UnknownHostException;
import java.util.concurrent.ThreadLocalRandom;
/**
* A universally unique identifier represented as a 64-bit numeric value.
*
* This implementation is based on Twitter's Snowflake id generation scheme. It uses a millisecond
* timestamp with Twitter's custom epoch for 41-bits, the machine's id for 10-bits (up to 1024
* machines), and a sequence number for 12-bits (rolls over at 4096).
*
* @author [email protected] (Ben Manes)
*/
public final class TracerIdGenerator {
private static final long EPOCH = 1288834974657L;
private static final int TIMESTAMP_SHIFT = 13;
private static final int MAX_MACHINE_ID = 1024;
private static final int MACHINE_ID_SHIFT = 54;
private static final long MACHINE_ID = getMachineId();
private static final int MAX_SEQUENCE_MASK = 4095;
private long lastTimestamp;
private int sequence;
/** @return a unique identifier */
public synchronized long nextId() {
initializeSeeds();
return ((lastTimestamp - EPOCH) << TIMESTAMP_SHIFT)
| (MACHINE_ID << MACHINE_ID_SHIFT)
| sequence;
}
/** Initializes the seed variables for generating the unique identifier. */
private void initializeSeeds() {
long timestamp = Math.max(lastTimestamp, System.currentTimeMillis());
if (timestamp == lastTimestamp) {
sequence = (sequence + 1) & MAX_SEQUENCE_MASK;
if (sequence == 0) {
timestamp += 1;
}
} else {
sequence = 0;
}
lastTimestamp = timestamp;
}
/** @return the machine's id based on its hardware address */
private static long getMachineId() {
try {
InetAddress ip = InetAddress.getLocalHost();
byte[] mac = NetworkInterface.getByInetAddress(ip).getHardwareAddress();
return ((0x000000FF & (long) mac[mac.length - 1])
| (0x0000FF00 & (((long) mac[mac.length - 2]) << 8))) >> 6;
} catch (SocketException | UnknownHostException e) {
return ThreadLocalRandom.current().nextLong(MAX_MACHINE_ID);
}
}
}