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Closure Compiler is a JavaScript optimizing compiler. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left. It also checks syntax, variable references, and types, and warns about common JavaScript pitfalls. It is used in many of Google's JavaScript apps, including Gmail, Google Web Search, Google Maps, and Google Docs.

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/*
 * Copyright 2017 The Closure Compiler Authors.
 *
 * 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.
 */

package com.google.javascript.jscomp;

import static java.util.concurrent.TimeUnit.SECONDS;

import com.google.common.collect.Iterables;
import com.google.common.util.concurrent.Futures;
import com.google.common.util.concurrent.ListenableFuture;
import com.google.common.util.concurrent.ListeningExecutorService;
import com.google.common.util.concurrent.MoreExecutors;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;

/**
 * A helper class to prebuild ASTs from a list of {@link CompilerInput}. Inputs are parsed into ASTs
 * the first time we try to get them. Get them all now using multiple threads, so they'll be parsed
 * in parallel and already available during the rest of the compilation.
 */
class PrebuildAst {
  private final AbstractCompiler compiler;
  private final int numParallelThreads;

  PrebuildAst(AbstractCompiler compiler, int numParalleThreads) {
    this.compiler = compiler;
    this.numParallelThreads = numParalleThreads;
  }

  void prebuild(Iterable allInputs) {
    ThreadFactory threadFactory =
        r -> {
          Thread t =
              new Thread(null, r, "jscompiler-PrebuildAst", CompilerExecutor.COMPILER_STACK_SIZE);
          t.setDaemon(true); // Do not prevent the JVM from exiting.
          return t;
        };
    ThreadPoolExecutor poolExecutor =
        new ThreadPoolExecutor(
            numParallelThreads,
            numParallelThreads,
            Integer.MAX_VALUE,
            SECONDS,
            new LinkedBlockingQueue(),
            threadFactory);
    ListeningExecutorService executorService = MoreExecutors.listeningDecorator(poolExecutor);
    List> futureList = new ArrayList<>(Iterables.size(allInputs));
    // TODO(moz): Support canceling all parsing on the first halting error
    for (final CompilerInput input : allInputs) {
      futureList.add(executorService.submit(() -> input.getAstRoot(compiler)));
    }

    poolExecutor.shutdown();
    try {
      Futures.allAsList(futureList).get();
    } catch (InterruptedException | ExecutionException e) {
      throw new RuntimeException(e);
    }
  }

}