根据twitter的snowflake算法生成唯一ID

C#版本

/// <summary>
/// 根据twitter的snowflake算法生成唯一ID
/// snowflake算法 64 位
/// 0---0000000000 0000000000 0000000000 0000000000 0 --- 00000 ---00000 ---000000000000
/// 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。
/// 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
/// </summary>
public class IdWorker
{
//机器ID
private static long workerId = 1;
private static long twepoch = 687888001020L; //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
private static long sequence = 0L;
private static int workerIdBits = 4; //机器码字节数。4个字节用来保存机器码
public static long maxWorkerId = -1L ^ -1L << workerIdBits; //最大机器ID
private static int sequenceBits = 10; //计数器字节数，10个字节用来保存计数码
private static int workerIdShift = sequenceBits; //机器码数据左移位数，就是后面计数器占用的位数
private static int timestampLeftShift = sequenceBits + workerIdBits; //时间戳左移动位数就是机器码和计数器总字节数
public static long sequenceMask = -1L ^ -1L << sequenceBits; //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
private long lastTimestamp = -1L;

public long nextId()
{
lock (this)
{
long timestamp = timeGen();
if (this.lastTimestamp == timestamp)
{ //同一微妙中生成ID
IdWorker.sequence = (IdWorker.sequence + 1) & IdWorker.sequenceMask; //用&运算计算该微秒内产生的计数是否已经到达上限
if (IdWorker.sequence == 0)
{
//一微妙内产生的ID计数已达上限，等待下一微妙
timestamp = tillNextMillis(this.lastTimestamp);
}
}
else
{ //不同微秒生成ID
IdWorker.sequence = 0; //计数清0
}
if (timestamp < lastTimestamp)
{ //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
throw new Exception(string.Format("Clock moved backwards.  Refusing to generate id for {0} milliseconds",
this.lastTimestamp - timestamp));
}
this.lastTimestamp = timestamp; //把当前时间戳保存为最后生成ID的时间戳
long nextId = (timestamp - twepoch << timestampLeftShift) | IdWorker.workerId << IdWorker.workerIdShift | IdWorker.sequence;
return nextId;
}
}

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

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

JAVA版本

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Component;

public class IdWorker {

protected static final Logger LOG = LoggerFactory.getLogger(IdWorker.class);

private long workerId;
private long datacenterId;
private long sequence = 0L;

private long twepoch = 1288834974657L;

private long workerIdBits = 5L;
private long datacenterIdBits = 5L;
private long maxWorkerId = -1L ^ (-1L << workerIdBits);
private long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
private long sequenceBits = 12L;

private long workerIdShift = sequenceBits;
private long datacenterIdShift = sequenceBits + workerIdBits;
private long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
private long sequenceMask = -1L ^ (-1L << sequenceBits);

private long lastTimestamp = -1L;

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

public synchronized long nextId() {
long timestamp = timeGen();

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

if (lastTimestamp == timestamp) {
sequence = (sequence + 1) & sequenceMask;
if (sequence == 0) {
timestamp = tilNextMillis(lastTimestamp);
}
} else {
sequence = 0L;
}

lastTimestamp = timestamp;

return ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence;
}

protected long tilNextMillis(long lastTimestamp) {
long timestamp = timeGen();
while (timestamp <= lastTimestamp) {
timestamp = timeGen();
}
return timestamp;
}

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

}