/*
* Copyright (C) 2015 Red Hat, Inc. and/or its affiliates.
*
* 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 org.jboss.errai.jpa.client.local;
public class LongIdGenerator<X> implements ErraiIdGenerator<Long> {
private final ErraiSingularAttribute<X, Long> attr;
/**
* The next ID we will attempt to return (after checking for collisions in the datastore).
*/
private long nextCandidateId = 1L;
/**
* When the next candidate ID value collides with a value in the database, we
* skip up to this many values in the sequence before trying again. The reason
* for the randomness is to avoid probing the same values again after a page
* reload.
*/
private final double probeJumpSize = 1000;
public LongIdGenerator(ErraiSingularAttribute<X, Long> attr) {
this.attr = attr;
}
/**
* We assume there is always the possibility to find another unused Long value.
*
* @return true
*/
@Override
public boolean hasNext(ErraiEntityManager entityManager) {
return true;
}
@Override
public Long next(ErraiEntityManager entityManager) {
while (entityManager.isKeyInUse(new Key<X, Long>((ErraiIdentifiableType<X>) attr.getDeclaringType(), nextCandidateId))) {
nextCandidateId += (long) (Math.random() * probeJumpSize);
// control rollover in case we run out of values
if (nextCandidateId >= Long.MAX_VALUE - probeJumpSize) {
nextCandidateId = 0;
}
}
return nextCandidateId++;
}
}