/*
* 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.beam.runners.core;
import javax.annotation.Nullable;
import org.apache.beam.sdk.transforms.windowing.BoundedWindow;
import org.apache.beam.sdk.values.PCollectionView;
/**
* The interface to objects that provide side inputs. Particular implementations
* may read a side input directly or use appropriate sorts of caching, etc.
*/
public interface SideInputReader {
/**
* Returns the value of the given {@link PCollectionView} for the given {@link BoundedWindow}.
*
* <p>It is valid for a side input to be {@code null}. It is <i>not</i> valid for this to
* return {@code null} for any other reason.
*/
@Nullable
<T> T get(PCollectionView<T> view, BoundedWindow window);
/**
* Returns true if the given {@link PCollectionView} is valid for this reader.
*/
<T> boolean contains(PCollectionView<T> view);
/**
* Returns true if there are no side inputs in this reader.
*/
boolean isEmpty();
}