/*
* 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.jctools.queues;
public final class IndexedQueueSizeUtil {
private IndexedQueueSizeUtil(){}
public interface IndexedQueue {
long lvConsumerIndex();
long lvProducerIndex();
}
public static int size(IndexedQueue iq) {
/*
* It is possible for a thread to be interrupted or reschedule between the read of the producer and
* consumer indices, therefore protection is required to ensure size is within valid range. In the
* event of concurrent polls/offers to this method the size is OVER estimated as we read consumer
* index BEFORE the producer index.
*/
long after = iq.lvConsumerIndex();
long size;
while (true) {
final long before = after;
final long currentProducerIndex = iq.lvProducerIndex();
after = iq.lvConsumerIndex();
if (before == after) {
size = (currentProducerIndex - after);
break;
}
}
// Long overflow is impossible (), so size is always positive. Integer overflow is possible for the unbounded
// indexed queues.
if (size > Integer.MAX_VALUE) {
return Integer.MAX_VALUE;
}
else {
return (int) size;
}
}
public static boolean isEmpty(IndexedQueue iq) {
// Order matters!
// Loading consumer before producer allows for producer increments after consumer index is read.
// This ensures this method is conservative in it's estimate. Note that as this is an MPMC there is
// nothing we can do to make this an exact method.
return (iq.lvConsumerIndex() == iq.lvProducerIndex());
}
}