| /* |
| * Copyright 2015 Open Networking Laboratory |
| * |
| * 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.onosproject.store.service; |
| |
| import java.util.concurrent.CompletableFuture; |
| |
| /** |
| * A distributed collection designed for holding elements prior to processing. |
| * A queue provides insertion, extraction and inspection operations. The extraction operation |
| * is designed to be non-blocking. |
| * |
| * @param <E> queue entry type |
| */ |
| public interface DistributedQueue<E> extends DistributedPrimitive { |
| |
| /** |
| * Returns total number of entries in the queue. |
| * @return queue size |
| */ |
| long size(); |
| |
| /** |
| * Returns true if queue has elements in it. |
| * @return true is queue has elements, false otherwise |
| */ |
| default boolean isEmpty() { |
| return size() == 0; |
| } |
| |
| /** |
| * Inserts an entry into the queue. |
| * @param entry entry to insert |
| */ |
| void push(E entry); |
| |
| /** |
| * If the queue is non-empty, an entry will be removed from the queue and the returned future |
| * will be immediately completed with it. If queue is empty when this call is made, the returned |
| * future will be eventually completed when an entry is added to the queue. |
| * @return queue entry |
| */ |
| CompletableFuture<E> pop(); |
| |
| /** |
| * Returns an entry from the queue without removing it. If the queue is empty returns null. |
| * @return queue entry or null if queue is empty |
| */ |
| E peek(); |
| } |