twitter的snowflake算法(C#版本)
转自:http://blog.csdn.net/kinwyb/article/details/50238505
使用twitter的snowflake算法生成唯一ID。
在分布式系统中,需要生成全局UID的场合还是比较多的,twitter的snowflake解决了这种需求,实现也还是很简单的,除去配置信息,核心代码就是毫秒级时间41位+机器ID 10位+毫秒内序列12位。
/// <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; 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 IdWorker(long workerId) { if (workerId > maxWorkerId || workerId < 0) throw new Exception(string.Format("worker Id can't be greater than {0} or less than 0 ", workerId)); IdWorker.workerId=workerId; } 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; } }