com.taobao.metamorphosis.utils.IdWorker Maven / Gradle / Ivy

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/*
 * (C) 2007-2012 Alibaba Group Holding Limited.
 * 
 * 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.
 */

/* Copyright 2010-2011 Twitter, Inc.*/
package com.taobao.metamorphosis.utils;

import com.taobao.metamorphosis.exception.InvalidSystemClock;


/**
 * ??????twitter??Ŀsnowflake??id??????????ȫ??Ψһ??ʱ??????
 * 
 * 
 * @see https://github.com/twitter/snowflake
 * @author boyan
 * @Date 2011-4-27
 * 
 */
public class IdWorker {
    private final long workerId;
    private final static long twepoch = 1303895660503L;
    private long sequence = 0L;
    private final static long workerIdBits = 10L;
    private final static long maxWorkerId = -1L ^ -1L << workerIdBits;
    private final static long sequenceBits = 12L;

    private final static long workerIdShift = sequenceBits;
    private final static long timestampLeftShift = sequenceBits + workerIdBits;
    private final static long sequenceMask = -1L ^ -1L << sequenceBits;

    private long lastTimestamp = -1L;


    public IdWorker(final long workerId) {
        super();
        if (workerId > this.maxWorkerId || workerId < 0) {
            throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0",
                this.maxWorkerId));
        }
        this.workerId = workerId;
    }


    public synchronized long nextId() {
        long timestamp = this.timeGen();
        if (this.lastTimestamp == timestamp) {
            this.sequence = this.sequence + 1 & this.sequenceMask;
            if (this.sequence == 0) {
                timestamp = this.tilNextMillis(this.lastTimestamp);
            }
        }
        else {
            this.sequence = 0;
        }
        if (timestamp < this.lastTimestamp) {
            throw new InvalidSystemClock(String.format(
                "Clock moved backwards.  Refusing to generate id for %d milliseconds", this.lastTimestamp - timestamp));
        }

        this.lastTimestamp = timestamp;
        return timestamp - twepoch << this.timestampLeftShift | this.workerId << this.workerIdShift | this.sequence;
    }


    private long tilNextMillis(final long lastTimestamp) {
        long timestamp = this.timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = this.timeGen();
        }
        return timestamp;
    }


    private long timeGen() {
        return System.currentTimeMillis();
    }

}