88 lines
3.2 KiB
Java
88 lines
3.2 KiB
Java
/*
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* Copyright (C) 2017 Google Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.google.copybara;
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import com.google.common.base.Preconditions;
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import com.google.common.base.Throwables;
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import com.google.common.collect.ImmutableList;
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import com.google.common.collect.Iterables;
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import com.google.common.collect.Lists;
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import com.google.common.util.concurrent.Futures;
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import com.google.common.util.concurrent.ListenableFuture;
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import com.google.common.util.concurrent.ListeningExecutorService;
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import com.google.common.util.concurrent.MoreExecutors;
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import com.google.copybara.exception.ValidationException;
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import java.io.IOException;
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import java.util.ArrayList;
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import java.util.List;
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import java.util.concurrent.ExecutionException;
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import java.util.concurrent.Executors;
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/**
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* A class that allows to run a list of things in parallel batches.
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*/
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public class LocalParallelizer {
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private final int threads;
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private final int minSize;
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private final ListeningExecutorService executor;
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public LocalParallelizer(int threads, int minSize) {
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this.threads = threads;
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this.minSize = minSize;
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Preconditions.checkState(threads >= 1, "Threads need to be positive");
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Preconditions.checkState(threads < 1000, "Too many threads (max: 1000)");
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executor = threads == 1
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? null
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: MoreExecutors.listeningDecorator(Executors.newFixedThreadPool(threads));
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}
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/**
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* Run a list of things in batches, calling {@code func} for each batch.
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*/
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public <K, V> List<V> run(Iterable<K> list, TransformFunc<K, V> func)
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throws IOException, ValidationException {
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if (threads == 1 || Iterables.size(list) < minSize) {
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return ImmutableList.of(func.run(list));
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}
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List<ListenableFuture<V>> results = new ArrayList<>(threads);
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List<K> newList = Lists.newArrayList(list);
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for (List<K> batch : Lists.partition(newList, Math.max(1, newList.size() / threads))) {
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results.add(executor.submit(() -> func.run(batch)));
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}
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try {
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return Futures.allAsList(results).get();
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} catch (InterruptedException e) {
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Thread.currentThread().interrupt();
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//TODO We cannot do much here. We might expose InterruptedException all the way up to Main...
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throw new RuntimeException("Interrupted", e);
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} catch (ExecutionException e) {
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Throwables.propagateIfPossible(e.getCause(), IOException.class, ValidationException.class);
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throw new RuntimeException("Unhandled error", e.getCause());
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}
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}
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/** Transforms a collection of K elements into T. */
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public interface TransformFunc<K, T> {
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/**
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* Execute oen batch. The number of elements is undefined.
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*/
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T run(Iterable<K> elements) throws IOException, ValidationException;
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}
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}
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