org.doomdark.uuid
Class UUIDTimer

java.lang.Object
  org.doomdark.uuid.UUIDTimer

public class UUIDTimer
extends java.lang.Object

UUIDTimer produces the time stamps required for time-based UUIDs. It works according to UUID-specification, with following modifications:

• Java libs can only product time stamps with maximum resolution of one millisecond. To compensate, an additional counter is used, so that more than one UUID can be generated between java clock updates. Counter may be used to generate up to 10000 UUIDs for each distrinct java clock value (which in some cases may mean getting 10k UUIDs for each 55 msecs, a la Windows, ie only about 200000 UUIDs per second).
• An additional precaution, counter is initialized not to 0 but to a random 8-bit number, and each time clock changes, lowest 8-bits of counter are preserved. The purpose it to make likelyhood of multi-JVM multi-instance generators to collide, without significantly reducing max. UUID generation speed. Note though that using more than one generator (from separate JVMs) is strongly discouraged, so hopefully this enhancement isn't needed. This 8-bit offset has to be reduced from total max. UUID count to preserve ordering property of UUIDs (ie. one can see which UUID was generated first for given UUID generator); the resulting 9500 UUIDs isn't much different from the optimal choice.

Some additional assumptions about calculating the timestamp:

• System.currentTimeMillis() is assumed to give time offset in UTC, or at least close enough thing to get correct timestamps. The alternate route would have to go through calendar object, use TimeZone offset to get to UTC, and then modify. Using currentTimeMillis should be much faster to allow rapid UUID creation.
• Similarly, the constant used for time offset between 1.1.1970 and start of Gregorian calendar is assumed to be correct (which seems to be the case when testing with Java calendars).

Constructor Summary

UUIDTimer(java.security.SecureRandom rnd)

Method Summary

void	getTimestamp(byte[] uuidData)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

UUIDTimer

public UUIDTimer(java.security.SecureRandom rnd)

Method Detail

getTimestamp

public void getTimestamp(byte[] uuidData)