在Java中创建唯一的时间戳

问题描述

我需要在Java中创建一个时间戳（以毫秒为单位），该时间戳在该特定VM实例中保证是唯一的。也就是说需要一些方法来扼制System.currentTimeMillis（）的吞吐量，以便每ms最多返回一个结果。

I need to create a timestamp (in milliseconds) in Java that is guaranteed to be unique in that particular VM-instance. I.e. need some way to throttle the throughput of System.currentTimeMillis() so that it returns at most one results every ms. Any ideas on how to implement that?

推荐答案

这将给出一个尽可能接近当前时间，没有重复的时间。 p>

This will give a time as close the current time as possible without duplicates.

private static final AtomicLong LAST_TIME_MS = new AtomicLong();
public static long uniqueCurrentTimeMS() {
    long now = System.currentTimeMillis();
    while(true) {
        long lastTime = LAST_TIME_MS.get();
        if (lastTime >= now)
            now = lastTime+1;
        if (LAST_TIME_MS.compareAndSet(lastTime, now))
            return now;
    }
}

一种方法是避免每毫米一个ID的限制 - 第二个是使用一个微秒的时间戳。即，将currentTimeMS乘以1000.这将允许每毫秒1000个id。

One way to avoid the limitation of one id per milli-second is to use a micro-second timestamp. i.e. multiply currentTimeMS by 1000. This will allow 1000 ids per milli-second.

注意：如果时间向后，例如由于NTP校正，每次调用1毫秒，直到时间赶上。 ;）

Note: if time goes backwards, eg due to an NTP correction, the time will just progress at 1 milli-second per invocation until time catches up. ;)

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