com.hazelcast.core.IdGenerator Maven / Gradle / Ivy
/*
* Copyright (c) 2008-2015, Hazelcast, Inc. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.hazelcast.core;
/**
* The IdGenerator is responsible for creating unique ids (a {@code long}) in a cluster.
*
* In theory a {@link com.hazelcast.core.IAtomicLong#incrementAndGet()} could be used to provide the same functionality.
* The big difference is that the incrementAndGet requires one or more remote calls for every invocation and therefor
* is a performance and scalability bottleneck. The IdGenerator uses an IAtomicLong under the hood, but instead of
* doing remote call for every call to {@link #newId()}, it does it less frequently. It checks out a chunk, e.g. 1..1000 and
* as long as it has not yet consumed all the ids in its chunk, then no remote call is done.
*
* It can be that ids generated by different cluster members will get out of order because each member will get its own chunk. It
* can be that member 1 has chunk 1..1000 and member 2 has 1001..2000. Therefore, member 2 will automatically have ids that
* are out of order with the ids generated by member 1.
*/
public interface IdGenerator extends DistributedObject {
/**
* Try to initialize this IdGenerator instance with the given id. The first
* generated id will be 1 greater than id.
*
* @return true if initialization succeeded, false if id is less than 0.
*/
boolean init(long id);
/**
* Generates and returns a cluster-wide unique id.
* Generated ids are guaranteed to be unique for the entire cluster
* as long as the cluster is live. If the cluster restarts, then
* id generation will start from 0.
*
* @return the cluster-wide new unique id
*/
long newId();
}