StefanRRichter commented on a change in pull request #8442: [FLINK-12483] Support (legacy) SourceFunction as special case in the mailbox model for stream tasks URL: https://github.com/apache/flink/pull/8442#discussion_r284669437
########## File path: flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/mailbox/MailboxReceiver.java ########## @@ -0,0 +1,59 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one + * or more contributor license agreements. See the NOTICE file + * distributed with this work for additional information + * regarding copyright ownership. The ASF licenses this file + * to you 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.apache.flink.streaming.runtime.tasks.mailbox; + +import javax.annotation.Nonnull; +import javax.annotation.Nullable; + +/** + * Consumer-facing side of the {@link Mailbox} interface. This is used to dequeue letters. The mailbox returns letters + * in the order by which they were enqueued. A mailbox should only be consumed by one thread at a time. + */ +public interface MailboxReceiver { + + /** + * Returns <code>true</code> if the mailbox contains mail. + */ + boolean hasMail(); + + /** + * Returns the oldest letter from the mailbox (head of queue) if the mailbox is not empty or + * <code>null</code> otherwise. + * + * @return the oldest letter from the mailbox (head of queue) if the mailbox is not empty or + * <code>null</code> otherwise. + */ + @Nullable + Runnable tryTakeMail(); Review comment: I would prefer to keep this as returning `null` because it is a data structure and therefore in line with what JDK queues etc do. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services
