/**
* Generate next unique ID.
*
* @throws IllegalStateException if the clock has gone backwards by more than {@code
* maxWaitForClockCatchupInMilliseconds}
* @return the next unique ID as a long value.
*/
public long getNextId() {
long timestamp = timeProvider.getTimeInMillis();
synchronized (syncObject) {
// Deal with the simple case first.
if (prevTimestamp < timestamp) {
sequence = 0L;
prevTimestamp = timestamp;
return buildKey(timestamp, workerId, sequence);
}
// TRICK: If the clock has gone backwards we can still use
// the sequence counter to generate unique IDs, so we
// reset the timestamp to prevTimestamp and try our luck
// with the sequence counter
timestamp = prevTimestamp;
// Invariant: we have handed out an ID for this timestamp
// Increment and wrap
sequence = ((sequence + 1) & sequenceBitMask);
if (0L == sequence) {
// The sequence has wrapped so we cheat and advance
// the timestamp by 1ms
timestamp++;
log.info("Cheating, advancing timestamp by 1ms. workerId = " + workerId);
prevTimestamp = timestamp;
}
return buildKey(timestamp, workerId, sequence);
}
}
private static long getCurrentTime() {
return PROVIDER.currentTimeMillis();
}