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 * Copyright (C) 2015 Google Inc.
 *
 * 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.
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package com.google.cloud.dataflow.sdk.runners.worker;

import com.google.cloud.dataflow.sdk.transforms.windowing.BoundedWindow;
import com.google.cloud.dataflow.sdk.util.PCollectionViewWindow;
import com.google.cloud.dataflow.sdk.util.SideInputReader;
import com.google.cloud.dataflow.sdk.util.Sized;
import com.google.cloud.dataflow.sdk.util.SizedSideInputReader;
import com.google.cloud.dataflow.sdk.values.PCollectionView;
import com.google.common.base.Throwables;
import com.google.common.cache.Cache;
import com.google.common.util.concurrent.UncheckedExecutionException;

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;

/**
 * A {@link SideInputReader} that maintains a cache of side inputs per window.
 *
 * 

For internal use only. * *

Package-private here so that the dependency on Guava does not leak into the public API * surface. Note that Guava is "shaded" so the {@code Cache} class here is not actually compatible * with a {@code Cache} created by anything other than the SDK. */ final class CachingSideInputReader extends SizedSideInputReader.Defaults implements SizedSideInputReader { private SizedSideInputReader subReader; private Cache, Sized> cache; private CachingSideInputReader( SizedSideInputReader subReader, Cache, Sized> cache) { this.subReader = subReader; this.cache = cache; } public static CachingSideInputReader of( SizedSideInputReader subReader, Cache, Sized> cache) { return new CachingSideInputReader(subReader, cache); } @Override public boolean contains(PCollectionView view) { return subReader.contains(view); } @Override public boolean isEmpty() { return subReader.isEmpty(); } @Override public Sized getSized( final PCollectionView view, final BoundedWindow window) { PCollectionViewWindow cacheKey = PCollectionViewWindow.of(view, window); try { @SuppressWarnings("unchecked") // safely uncasting the thing from the callback Sized sideInputContents = (Sized) cache.get(cacheKey, new Callable>() { @Override public Sized call() { @SuppressWarnings("unchecked") // safe covariant cast Sized value = (Sized) subReader.getSized(view, window); return value; } }); return sideInputContents; } catch (ExecutionException | UncheckedExecutionException exc) { throw Throwables.propagate(exc.getCause()); } } }