[GitHub] [flink] pnowojski commented on a change in pull request #8467: [FLINK-12535][network] Make CheckpointBarrierHandler non-blocking

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pnowojski commented on a change in pull request #8467: [FLINK-12535][network] Make CheckpointBarrierHandler non-blocking
URL: https://github.com/apache/flink/pull/8467#discussion_r285910390
 
 

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 File path: flink-runtime/src/main/java/org/apache/flink/runtime/io/AsyncDataInput.java
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 @@ -0,0 +1,50 @@
+/*
+ * 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.runtime.io;
+
+import java.util.concurrent.CompletableFuture;
+
+/**
+ * Interface defining couple of essential methods for asynchronous and non blocking data polling.
+ */
+public interface AsyncDataInput<T> {
+	CompletableFuture<?> AVAILABLE = CompletableFuture.completedFuture(null);
+
+	/**
+	 * Poll the next element.
+	 *
+	 * @return If the {@link T} is an {@code Optional}:
+	 * 1. return {@code Optional.of(element)} - next returned element. {@code Optional.empty()} will
+	 * be returned if there is no data to return or if {@link #isFinished()} returns true.
+	 * otherwise:
+	 * 2. next element or null if there is no data to return or if {@link #isFinished()} returns true.
+	 */
+	T pollNext() throws Exception;
 
 Review comment:
   I don't know what should I mention here. Different implementations might want to throw different kind of exceptions.

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