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package bitronix.tm.utils;

import bitronix.tm.BitronixXid;
import bitronix.tm.TransactionManagerServices;

/**
 * Helper that offers UID generation (GTRID, XID, sequences) needed by the transaction manager.
 * 

Generated UIDs are at most 64 bytes long and are made of 3 subparts: the current time in milliseconds since * Epoch, a JVM transient atomic sequence number and the configured bitronix.tm.serverId.

*

The reliance on the system clock is critical to the uniqueness of the UID in the network so you have to make sure * all servers of the network running this transaction manager have their clock reasonably in sync. An order of 1 * second synchronicity is generally fine.

*

© Bitronix Software

* * @author lorban */ public class UidGenerator { private static int sequenceNumber = 0; /** * Generate a UID, globally unique. This method relies on the configured serverId for network uniqueness. * @return the generated UID. */ public static Uid generateUid() { byte[] timestamp = Encoder.longToBytes(System.currentTimeMillis()); byte[] sequence = Encoder.intToBytes(getNextSequenceNumber()); byte[] serverId = TransactionManagerServices.getConfiguration().buildServerIdArray(); int uidLength = serverId.length + timestamp.length + sequence.length; byte[] uidArray = new byte[uidLength]; System.arraycopy(serverId, 0, uidArray, 0, serverId.length); System.arraycopy(timestamp, 0, uidArray, serverId.length, timestamp.length); System.arraycopy(sequence, 0, uidArray, serverId.length + timestamp.length, sequence.length); return new Uid(uidArray); } /** * Atomically generate general-purpose sequence numbers starting at 0. The counter is reset at every * JVM startup. * @return a sequence number unique for the lifespan of this JVM. */ public static synchronized int getNextSequenceNumber() { return sequenceNumber++; } /** * Generate a XID with the specified globalTransactionId. * @param gtrid the GTRID to use to generate the Xid. * @return the generated Xid. */ public static BitronixXid generateXid(Uid gtrid) { return new BitronixXid(gtrid, generateUid()); } }




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