Chemmy's Blog

根据twitter的snowflake算法生成唯一ID - 梁照彬 - 博客园

Excerpt

C#版本 JAVA版本

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C#版本

<span>///</span> <span>&lt;summary&gt;</span>
    <span>///</span><span> 根据twitter的snowflake算法生成唯一ID
    </span><span>///</span><span> snowflake算法 64 位
    </span><span>///</span><span> 0---0000000000 0000000000 0000000000 0000000000 0 --- 00000 ---00000 ---000000000000
    </span><span>///</span><span> 第一位为未使用（实际上也可作为long的符号位），接下来的41位为毫秒级时间，然后5位datacenter标识位，5位机器ID（并不算标识符，实际是为线程标识），然后12位该毫秒内的当前毫秒内的计数，加起来刚好64位，为一个Long型。
    </span><span>///</span><span> 其中datacenter标识位起始是机器位，机器ID其实是线程标识，可以同一一个10位来表示不同机器
    </span><span>///</span> <span>&lt;/summary&gt;</span>
    <span>public</span> <span>class</span><span> IdWorker
    {
        </span><span>//</span><span>机器ID</span>
        <span>private</span> <span>static</span> <span>long</span> workerId = <span>1</span><span>;
        </span><span>private</span> <span>static</span> <span>long</span> twepoch = <span>687888001020L</span>; <span>//</span><span>唯一时间，这是一个避免重复的随机量，自行设定不要大于当前时间戳</span>
        <span>private</span> <span>static</span> <span>long</span> sequence = <span>0L</span><span>;
        </span><span>private</span> <span>static</span> <span>int</span> workerIdBits = <span>4</span>; <span>//</span><span>机器码字节数。4个字节用来保存机器码</span>
        <span>public</span> <span>static</span> <span>long</span> maxWorkerId = -<span>1L</span> ^ -<span>1L</span> &lt;&lt; workerIdBits; <span>//</span><span>最大机器ID</span>
        <span>private</span> <span>static</span> <span>int</span> sequenceBits = <span>10</span>; <span>//</span><span>计数器字节数，10个字节用来保存计数码</span>
        <span>private</span> <span>static</span> <span>int</span> workerIdShift = sequenceBits; <span>//</span><span>机器码数据左移位数，就是后面计数器占用的位数</span>
        <span>private</span> <span>static</span> <span>int</span> timestampLeftShift = sequenceBits + workerIdBits; <span>//</span><span>时间戳左移动位数就是机器码和计数器总字节数</span>
        <span>public</span> <span>static</span> <span>long</span> sequenceMask = -<span>1L</span> ^ -<span>1L</span> &lt;&lt; sequenceBits; <span>//</span><span>一微秒内可以产生计数，如果达到该值则等到下一微妙在进行生成</span>
        <span>private</span> <span>long</span> lastTimestamp = -<span>1L</span><span>;

        </span><span>public</span> <span>long</span><span> nextId()
        {
            </span><span>lock</span> (<span>this</span><span>)
            {
                </span><span>long</span> timestamp =<span> timeGen();
                </span><span>if</span> (<span>this</span>.lastTimestamp ==<span> timestamp)
                { </span><span>//</span><span>同一微妙中生成ID</span>
                    IdWorker.sequence = (IdWorker.sequence + <span>1</span>) &amp; IdWorker.sequenceMask; <span>//</span><span>用&amp;运算计算该微秒内产生的计数是否已经到达上限</span>
                    <span>if</span> (IdWorker.sequence == <span>0</span><span>)
                    {
                        </span><span>//</span><span>一微妙内产生的ID计数已达上限，等待下一微妙</span>
                        timestamp = tillNextMillis(<span>this</span><span>.lastTimestamp);
                    }
                }
                </span><span>else</span><span>
                { </span><span>//</span><span>不同微秒生成ID</span>
                    IdWorker.sequence = <span>0</span>; <span>//</span><span>计数清0</span>
<span>                }
                </span><span>if</span> (timestamp &lt;<span> lastTimestamp)
                { </span><span>//</span><span>如果当前时间戳比上一次生成ID时时间戳还小，抛出异常，因为不能保证现在生成的ID之前没有生成过</span>
                    <span>throw</span> <span>new</span> Exception(<span>string</span>.Format(<span>"</span><span>Clock moved backwards.  Refusing to generate id for {0} milliseconds</span><span>"</span><span>,
                        </span><span>this</span>.lastTimestamp -<span> timestamp));
                }
                </span><span>this</span>.lastTimestamp = timestamp; <span>//</span><span>把当前时间戳保存为最后生成ID的时间戳</span>
                <span>long</span> nextId = (timestamp - twepoch &lt;&lt; timestampLeftShift) | IdWorker.workerId &lt;&lt; IdWorker.workerIdShift |<span> IdWorker.sequence;
                </span><span>return</span><span> nextId;
            }
        }

        </span><span>///</span> <span>&lt;summary&gt;</span>
        <span>///</span><span> 获取下一微秒时间戳
        </span><span>///</span> <span>&lt;/summary&gt;</span>
        <span>///</span> <span>&lt;param name="lastTimestamp"&gt;&lt;/param&gt;</span>
        <span>///</span> <span>&lt;returns&gt;&lt;/returns&gt;</span>
        <span>private</span> <span>long</span> tillNextMillis(<span>long</span><span> lastTimestamp)
        {
            </span><span>long</span> timestamp =<span> timeGen();
            </span><span>while</span> (timestamp &lt;=<span> lastTimestamp)
            {
                timestamp </span>=<span> timeGen();
            }
            </span><span>return</span><span> timestamp;
        }

        </span><span>///</span> <span>&lt;summary&gt;</span>
        <span>///</span><span> 生成当前时间戳
        </span><span>///</span> <span>&lt;/summary&gt;</span>
        <span>///</span> <span>&lt;returns&gt;&lt;/returns&gt;</span>
        <span>private</span> <span>long</span><span> timeGen()
        {
            </span><span>return</span> (<span>long</span>)(DateTime.UtcNow - <span>new</span> DateTime(<span>1970</span>, <span>1</span>, <span>1</span>, <span>0</span>, <span>0</span>, <span>0</span><span>, DateTimeKind.Utc)).TotalMilliseconds;
        }
    }</span>

JAVA版本

<span>import</span><span> org.slf4j.Logger;
</span><span>import</span><span> org.slf4j.LoggerFactory;
</span><span>import</span><span> org.springframework.stereotype.Component;
</span>
<span>public</span> <span>class</span><span> IdWorker {

    </span><span>protected</span> <span>static</span> <span>final</span> Logger LOG = LoggerFactory.getLogger(IdWorker.<span>class</span><span>);

    </span><span>private</span> <span>long</span><span> workerId;
    </span><span>private</span> <span>long</span><span> datacenterId;
    </span><span>private</span> <span>long</span> sequence = 0L<span>;

    </span><span>private</span> <span>long</span> twepoch = 1288834974657L<span>;

    </span><span>private</span> <span>long</span> workerIdBits = 5L<span>;
    </span><span>private</span> <span>long</span> datacenterIdBits = 5L<span>;
    </span><span>private</span> <span>long</span> maxWorkerId = -1L ^ (-1L &lt;&lt;<span> workerIdBits);
    </span><span>private</span> <span>long</span> maxDatacenterId = -1L ^ (-1L &lt;&lt;<span> datacenterIdBits);
    </span><span>private</span> <span>long</span> sequenceBits = 12L<span>;

    </span><span>private</span> <span>long</span> workerIdShift =<span> sequenceBits;
    </span><span>private</span> <span>long</span> datacenterIdShift = sequenceBits +<span> workerIdBits;
    </span><span>private</span> <span>long</span> timestampLeftShift = sequenceBits + workerIdBits +<span> datacenterIdBits;
    </span><span>private</span> <span>long</span> sequenceMask = -1L ^ (-1L &lt;&lt;<span> sequenceBits);

    </span><span>private</span> <span>long</span> lastTimestamp = -1L<span>;

    </span><span>public</span> IdWorker(<span>long</span> workerId, <span>long</span><span> datacenterId) {
        </span><span>//</span><span> sanity check for workerId</span>
        <span>if</span> (workerId &gt; maxWorkerId || workerId &lt; 0<span>) {
            </span><span>throw</span> <span>new</span> IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0"<span>, maxWorkerId));
        }
        </span><span>if</span> (datacenterId &gt; maxDatacenterId || datacenterId &lt; 0<span>) {
            </span><span>throw</span> <span>new</span> IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0"<span>, maxDatacenterId));
        }
        </span><span>this</span>.workerId =<span> workerId;
        </span><span>this</span>.datacenterId =<span> datacenterId;
        LOG.info(String.format(</span>"worker starting. timestamp left shift %d, datacenter id bits %d, worker id bits %d, sequence bits %d, workerid %d"<span>, timestampLeftShift, datacenterIdBits, workerIdBits, sequenceBits, workerId));
    }

    </span><span>public</span> <span>synchronized</span> <span>long</span><span> nextId() {
        </span><span>long</span> timestamp =<span> timeGen();

        </span><span>if</span> (timestamp &lt;<span> lastTimestamp) {
            LOG.error(String.format(</span>"clock is moving backwards.  Rejecting requests until %d."<span>, lastTimestamp));
            </span><span>throw</span> <span>new</span> RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp -<span> timestamp));
        }

        </span><span>if</span> (lastTimestamp ==<span> timestamp) {
            sequence </span>= (sequence + 1) &amp;<span> sequenceMask;
            </span><span>if</span> (sequence == 0<span>) {
                timestamp </span>=<span> tilNextMillis(lastTimestamp);
            }
        } </span><span>else</span><span> {
            sequence </span>= 0L<span>;
        }

        lastTimestamp </span>=<span> timestamp;

        </span><span>return</span> ((timestamp - twepoch) &lt;&lt; timestampLeftShift) | (datacenterId &lt;&lt; datacenterIdShift) | (workerId &lt;&lt; workerIdShift) |<span> sequence;
    }

    </span><span>protected</span> <span>long</span> tilNextMillis(<span>long</span><span> lastTimestamp) {
        </span><span>long</span> timestamp =<span> timeGen();
        </span><span>while</span> (timestamp &lt;=<span> lastTimestamp) {
            timestamp </span>=<span> timeGen();
        }
        </span><span>return</span><span> timestamp;
    }

    </span><span>protected</span> <span>long</span><span> timeGen() {
        </span><span>return</span><span> System.currentTimeMillis();
    }


}</span>