com.wl4g.infra.common.id.SnowflakeIdGenerator Maven / Gradle / Ivy
The newest version!
/*
* Copyright 2017 ~ 2025 the original author or authors. James Wong
*
* 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.wl4g.infra.common.id;
import static com.wl4g.infra.common.lang.Assert2.isTrueOf;
import static com.wl4g.infra.common.lang.Assert2.notNullOf;
import static java.lang.String.format;
import java.util.concurrent.atomic.AtomicLong;
/**
* Snowflake algorithms Id generator.
*
* @author James Wong
* @version v1.0 2018年6月10日
* @since
* @see https://github.com/twitter/snowflake
*/
public class SnowflakeIdGenerator {
/**
* {@link BitsDefine}
*/
private final BitsDefine def;
// Worker node ID.
private final long workerId;
// Data center ID.
private final long dataCenterId;
// Sequence ID.
private final AtomicLong sequence = new AtomicLong(0L);
// Last generate timestamp.
private final AtomicLong lastTime = new AtomicLong(-1L);
public SnowflakeIdGenerator() {
this(BitsDefine.StandardSafeJs, 0L, 0L, 0L);
}
public SnowflakeIdGenerator(BitsDefine def, long workerId, long dataCenterId, long sequence) {
validate(def, workerId, dataCenterId, sequence);
this.def = def;
this.workerId = workerId;
this.dataCenterId = dataCenterId;
this.sequence.set(sequence);
}
/**
* Gets next global UID.
*
* @return
*/
public synchronized long nextId() {
long now = timeGen();
// 如果服务器时间有问题(时钟后退) 报错。
if (now < lastTime.get()) {
throw new IllegalStateException(
format("Clock moved backwards. Refusing to generate id for %d milliseconds", lastTime.get() - now));
}
// 如果上次生成时间和当前时间相同,在同一毫秒内
if (lastTime.get() == now) {
// sequence自增，因为sequence只有12bit，所以和sequenceMask相与一下，去掉高位
sequence.set(sequence.incrementAndGet() & def.sequenceMask);
// 判断是否溢出,也就是每毫秒内超过4095，当为4096时，与sequenceMask相与，sequence就等于0
if (sequence.get() == 0) {
// 自旋等待到下一毫秒
now = tilNextMillis(lastTime.get());
}
} else {
// 如果和上次生成时间不同,重置sequence，就是下一毫秒开始，sequence计数重新从0开始累加
sequence.set(0L);
}
lastTime.set(now);
// Finally, the ID is calculated according to the rules.
// 000000000000000000000000000000000000000000 00000 00000 000000000000
// time dataCenterId workerId sequence
return ((now - def.twepoch) << def.timestampLeftShift) | (dataCenterId << def.dataCenterIdShift)
| (workerId << def.workerIdShift) | sequence.get();
}
/**
* Spin wait until next MS
*
* @param lastTimestamp
* @return
*/
protected long tilNextMillis(long lastTimestamp) {
long timestamp = timeGen();
while (timestamp <= lastTimestamp) {
timestamp = timeGen();
}
return timestamp;
}
/**
* Gets now timestamp.
*
* @return
*/
protected long timeGen() {
return System.currentTimeMillis();
}
/**
* Validation bits definition options.
*
* @param def
* @param workerId
* @param dataCenterId
* @param sequence
*/
private void validate(BitsDefine def, long workerId, long dataCenterId, long sequence) {
notNullOf(def, "bitsDefine");
isTrueOf(workerId >= 0, "workerId>=0");
isTrueOf(dataCenterId >= 0, "dataCenterId>=0");
isTrueOf(sequence >= 0, "sequence>=0");
isTrueOf(def.sequenceBits >= 0, "sequenceBits>=0");
if (workerId > def.maxWorkerId || workerId < 0) {
throw new IllegalArgumentException(format("worker Id can't be greater than %d or less than 0", def.maxWorkerId));
}
if (dataCenterId > def.maxDatacenterId || dataCenterId < 0) {
throw new IllegalArgumentException(
format("datacenter Id can't be greater than %d or less than 0", def.maxDatacenterId));
}
}
/**
* Gets {@link SnowflakeIdGenerator} default instance.
*
* @return
*/
public final static SnowflakeIdGenerator getDefault() {
return SingletionHolder.instance;
}
/**
* {@link SingletionHolder} singletion holder
*
* @author James Wong
* @version v1.0 2020年6月10日
* @since
*/
private static final class SingletionHolder {
private static final SnowflakeIdGenerator instance = new SnowflakeIdGenerator();
}
/**
* {@link BitsDefine}
*
* @author James Wong
* @version v1.0 2020-10-09
* @since
*/
public static final class BitsDefine {
// Epoch (e.g: 1288834974657L => Thu, 04 Nov 2010 01:42:54 GMT)
final long twepoch;
// Node ID length bits.
final long workerIdBits;
// Data Center ID length bits.
final long dataCenterIdBits;
// The maximum number of machine nodes supported is 0-31, a total of 32
final long maxWorkerId;
// The maximum number of data center nodes supported is 0-31, a total of
// 32
final long maxDatacenterId;
// Serial number length bits.
final long sequenceBits;
// Machine node left shift length bits.
final long workerIdShift;
// Data center node moves length bits.
final long dataCenterIdShift;
// Time milliseconds shift length bits.
final long timestampLeftShift;
// Sequence mask bits.
final long sequenceMask;
public BitsDefine(long twepoch, long workerIdBits, long dataCenterIdBits, long sequenceBits) {
this.twepoch = twepoch;
this.workerIdBits = workerIdBits;
this.dataCenterIdBits = dataCenterIdBits;
// The maximum number of machine nodes supported is 0-31, a total of
// 32
this.maxWorkerId = -1L ^ (-1L << workerIdBits);
// The maximum number of data center nodes supported is 0-31, a
// total of 32
this.maxDatacenterId = -1L ^ (-1L << dataCenterIdBits);
// Serial number. (e.g: 12 digits)
this.sequenceBits = sequenceBits;
// Machine node left shift bits. (e.g: 12 bits)
this.workerIdShift = sequenceBits;
// Data center node moves left bits. (e.g: 17 bits)
this.dataCenterIdShift = sequenceBits + workerIdBits;
// Time milliseconds shift left bits. (e.g: 22 bits)
this.timestampLeftShift = sequenceBits + workerIdBits + dataCenterIdBits;
// Sequence mask bits. (e.g: 4095 bits).
this.sequenceMask = -1L ^ (-1L << sequenceBits);
// Validation
isTrueOf(twepoch >= 0, "twepoch>=0");
isTrueOf(workerIdBits >= 0, "workerIdBits>=0");
isTrueOf(dataCenterIdBits >= 0, "dataCenterIdBits>=0");
isTrueOf(sequenceBits >= 0, "sequenceBits>=0");
}
/**
* Generates a decimal integer with a maximum length of 16, which is
* JavaScript compatible (i.e., IEEE 754 specification).
*
*
* twepoch=1288834974657L => Thu, 04 Nov 2010 01:42:54 GMT
*
*/
public static final BitsDefine StandardSafeJs = new BitsDefine(1288834974657L, 2L, 2L, 10L);
/**
* Generates a decimal integer with a maximum length of 19. Note:
* that it is not compatible with JavaScript (does not follow the IEEE
* 754 specification), and is suitable for high concurrency and non web
* browser systems. The system of web browser recommends using the safe
* option: {@link #StandardSafeJs}.
*
*
* twepoch=1288834974657L => Thu, 04 Nov 2010 01:42:54 GMT
*
*/
public static final BitsDefine LargeUnsafeJs = new BitsDefine(1288834974657L, 5L, 5L, 12L);
}
}