com.github.drinkjava2.jdialects.id.SnowflakeCreator Maven / Gradle / Ivy
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/*
* Copyright 2016 the original author or authors.
*
* 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.drinkjava2.jdialects.id;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.concurrent.atomic.AtomicLong;
/**
* java edition of Twitter Snowflake, a network service for generating
* unique ID numbers at high scale with some simple guarantees.
*
* https://github.com/twitter/snowflake
*
* Usage example: long id= new SnowflakeCreator(5L,5L, 18, 31).nextId();
*
* P1 is datacenterIdBits, 1~9 bits
* P2 is workerIdBits, 1~9 bits
* P3 is real datacenterId, 0 to 511
* P4 is real workerId, 0 to 511
*
* Should: P1 + P2 = 10 (2^10=1024)
*
* Should: P3 + P4 < 1024
*
*
* @author downgoon
* @author Yong Z.
*/
@SuppressWarnings("all")
public class SnowflakeCreator {
/*
* bits allocations
*/
private long datacenterIdBits = 5L;
private long workerIdBits = 5L;
private final long datacenterId;
private final long workerId;
/*
* max values of datacenterId and WorkerId
*/
private long maxDatacenterId = -1L ^ (-1L << datacenterIdBits); // 2^5-1
private long maxWorkerId = -1L ^ (-1L << workerIdBits); // 2^5-1
private final long unusedBits = 1L;
/**
* 'time stamp' here is defined as the number of millisecond that have elapsed
* since the {@link #epoch} given by users on {@link SnowflakeGenerator}
* instance initialization
*/
private final long timestampBits = 41L;
private final long sequenceBits = 12L;
/*
* max values of timeStamp and sequence
*/
private final long maxSequence = -1L ^ (-1L << sequenceBits); // 2^12-1
/**
* left shift bits of timeStamp, workerId and datacenterId
*/
private final long timestampShift = sequenceBits + datacenterIdBits + workerIdBits;
private final long datacenterIdShift = sequenceBits + workerIdBits;
private final long workerIdShift = sequenceBits;
/*
* object status variables
*/
/**
* reference material of 'time stamp' is '2016-01-01'. its value can't be
* modified after initialization.
*/
private final long epoch = 1451606400000L;
/**
* the unique and incrementing sequence number scoped in only one period/unit
* (here is ONE millisecond). its value will be increased by 1 in the same
* specified period and then reset to 0 for next period.
*
* max: 2^12-1 range: [0,4095]
*/
private long sequence = 0L;
/** the time stamp last snowflake ID generated */
private long lastTimestamp = -1L;
/**
* generate an unique and incrementing id
*
* @return id
*/
public synchronized long nextId() {
long currTimestamp = timestampGen();
if (currTimestamp < lastTimestamp) {
throw new IllegalStateException(
String.format("Clock moved backwards. Refusing to generate id for %d milliseconds",
lastTimestamp - currTimestamp));
}
if (currTimestamp == lastTimestamp) {
sequence = (sequence + 1) & maxSequence;
if (sequence == 0) { // overflow: greater than max sequence
currTimestamp = waitNextMillis(currTimestamp);
}
} else { // reset to 0 for next period/millisecond
sequence = 0L;
}
// track and memo the time stamp last snowflake ID generated
lastTimestamp = currTimestamp;
return ((currTimestamp - epoch) << timestampShift) | //
(datacenterId << datacenterIdShift) | //
(workerId << workerIdShift) | // new line for nice looking
sequence;
}
/**
* @param datacenterId
* data center number the process running on, value range: [0,31]
* @param workerId
* machine or process number, value range: [0,31]
*/
public SnowflakeCreator(long datacenterIdBits, long workerIdBits, long datacenterId, long workerId) {
this.datacenterIdBits = datacenterIdBits;
this.workerIdBits = workerIdBits;
maxDatacenterId = -1L ^ (-1L << datacenterIdBits); // 2^5-1
maxWorkerId = -1L ^ (-1L << workerIdBits); // 2^5-1
if (datacenterId > maxDatacenterId || datacenterId < 0) {
throw new IllegalArgumentException(
String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
}
if (workerId > maxWorkerId || workerId < 0) {
throw new IllegalArgumentException(
String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
}
this.datacenterId = datacenterId;
this.workerId = workerId;
}
/**
* track the amount of calling {@link #waitNextMillis(long)} method
*/
private final AtomicLong waitCount = new AtomicLong(0);
/**
* @return the amount of calling {@link #waitNextMillis(long)} method
*/
public long getWaitCount() {
return waitCount.get();
}
/**
* running loop blocking until next millisecond
*
* @param currTimestamp
* current time stamp
* @return current time stamp in millisecond
*/
protected long waitNextMillis(long currTimestamp) {
waitCount.incrementAndGet();
while (currTimestamp <= lastTimestamp) {
currTimestamp = timestampGen();
}
return currTimestamp;
}
/**
* get current time stamp
*
* @return current time stamp in millisecond
*/
protected long timestampGen() {
return System.currentTimeMillis();
}
/**
* show settings of Snowflake
*/
@Override
public String toString() {
return "Snowflake Settings [timestampBits=" + timestampBits + ", datacenterIdBits=" + datacenterIdBits
+ ", workerIdBits=" + workerIdBits + ", sequenceBits=" + sequenceBits + ", epoch=" + epoch
+ ", datacenterId=" + datacenterId + ", workerId=" + workerId + "]";
}
public long getEpoch() {
return this.epoch;
}
/**
* extract time stamp, datacenterId, workerId and sequence number information
* from the given id
*
* @param id
* a snowflake id generated by this object
* @return an array containing time stamp, datacenterId, workerId and sequence
* number
*/
public long[] parseId(long id) {
long[] arr = new long[5];
arr[4] = ((id & diode(unusedBits, timestampBits)) >> timestampShift);
arr[0] = arr[4] + epoch;
arr[1] = (id & diode(unusedBits + timestampBits, datacenterIdBits)) >> datacenterIdShift;
arr[2] = (id & diode(unusedBits + timestampBits + datacenterIdBits, workerIdBits)) >> workerIdShift;
arr[3] = (id & diode(unusedBits + timestampBits + datacenterIdBits + workerIdBits, sequenceBits));
return arr;
}
/**
* extract and display time stamp, datacenterId, workerId and sequence number
* information from the given id in humanization format
*
* @param id
* snowflake id in Long format
* @return snowflake id in String format
*/
public String formatId(long id) {
long[] arr = parseId(id);
String tmf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS").format(new Date(arr[0]));
return String.format("%s, #%d, @(%d,%d)", tmf, arr[3], arr[1], arr[2]);
}
/**
* a diode is a long value whose left and right margin are ZERO, while middle
* bits are ONE in binary string layout. it looks like a diode in shape.
*
* @param offset
* left margin position
* @param length
* offset+length is right margin position
* @return a long value
*/
private long diode(long offset, long length) {
int lb = (int) (64 - offset);
int rb = (int) (64 - (offset + length));
return (-1L << lb) ^ (-1L << rb);
}
}