/*
* Bitronix Transaction Manager
*
* Copyright (c) 2010, Bitronix Software.
*
* This copyrighted material is made available to anyone wishing to use, modify,
* copy, or redistribute it subject to the terms and conditions of the GNU
* Lesser General Public License, as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License
* for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this distribution; if not, write to:
* Free Software Foundation, Inc.
* 51 Franklin Street, Fifth Floor
* Boston, MA 02110-1301 USA
*/
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.
* <p>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 <code>bitronix.tm.serverId</code>.</p>
* <p>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.</p>
*
* @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());
}
}