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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 2008 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 com.google.common.collect.ImmutableMap;
import com.google.common.collect.Maps;
import com.google.javascript.jscomp.CodeChangeHandler.RecentChange;
import com.google.javascript.rhino.Node;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Map;
import java.util.zip.GZIPOutputStream;

/**
 */
public class PerformanceTracker {

  private final Node jsRoot;
  private final boolean trackGzippedSize;

  // Keeps track of AST changes and computes code size estimation
  // if there is any.
  private final RecentChange codeChange = new RecentChange();

  private int curCodeSizeEstimate = -1;
  private int curZippedCodeSizeEstimate = -1;

  private Deque currentRunningPass = new ArrayDeque();

  /** Maps pass name to total time spend. */
  private final Map runtimeRecord = Maps.newHashMap();

  /** Maps pass name to total size reduction. */
  private final Map codeSizeRecord = Maps.newHashMap();

  /** Maps pass name to total size reduction. */
  private final Map zippedCodeSizeRecord = Maps.newHashMap();

  PerformanceTracker(Node jsRoot, boolean trackGzippedSize) {
    this.jsRoot = jsRoot;
    this.trackGzippedSize = trackGzippedSize;
  }

  CodeChangeHandler getCodeChangeHandler() {
    return codeChange;
  }

  void recordPassStart(String passName) {
    currentRunningPass.push(passName);
    codeChange.reset();
  }

  /**
   * Record that a pass has stopped.
   *
   * @param passName Short name of the pass.
   * @param result Execution time.
   */
  void recordPassStop(String passName, long result) {
    String currentPassName = currentRunningPass.pop();
    if (!passName.equals(currentPassName)) {
      throw new RuntimeException(passName + " is not running.");
    }
    Long total = runtimeRecord.get(passName);
    if (total == null) {
      total = 0L;
    }
    total = total.longValue() + result;
    runtimeRecord.put(passName, total);

    if (codeChange.hasCodeChanged()) {
      CodeSizeEstimatePrinter printer = estimateCodeSize(jsRoot);
      curCodeSizeEstimate = recordSizeChange(curCodeSizeEstimate,
          printer.calcSize(), passName, codeSizeRecord);
      curZippedCodeSizeEstimate = recordSizeChange(curZippedCodeSizeEstimate,
          printer.calcZippedSize(), passName, zippedCodeSizeRecord);
    }
  }

  /**
   * Record the size change in the given record for that given pass.
   *
   * @return The new estimated size.
   */
  private static int recordSizeChange(int oldSize, int newSize, String passName,
      Map record) {
    if (oldSize != -1) {
      int delta = oldSize - newSize;
      Integer reduction = record.get(passName);
      if (delta > 0) {
        if (reduction == null) {
          reduction = delta;
        } else {
          reduction = reduction + delta;
        }
        record.put(passName, reduction);
      }
    }
    return newSize;
  }


  public ImmutableMap getRuntimeRecord() {
    return ImmutableMap.copyOf(runtimeRecord);
  }

  public ImmutableMap getCodeSizeRecord() {
    return ImmutableMap.copyOf(codeSizeRecord);
  }

  public ImmutableMap getZippedCodeSizeRecord() {
    return ImmutableMap.copyOf(zippedCodeSizeRecord);
  }

  private final CodeSizeEstimatePrinter estimateCodeSize(Node root) {
    CodeSizeEstimatePrinter cp = new CodeSizeEstimatePrinter(trackGzippedSize);
    CodeGenerator cg = new CodeGenerator(cp);
    cg.add(root);
    return cp;
  }

  /**
   * Purely use to get a code size estimate and not generate any code at all.
   */
  private static final class CodeSizeEstimatePrinter extends CodeConsumer {
    private final boolean trackGzippedSize;
    private int size = 0;
    private char lastChar = '\0';
    private final ByteArrayOutputStream output = new ByteArrayOutputStream();
    private final GZIPOutputStream stream;

    private CodeSizeEstimatePrinter(boolean trackGzippedSize) {
      this.trackGzippedSize = trackGzippedSize;

      try {
        stream = new GZIPOutputStream(output);
      } catch (IOException e) {
        throw new RuntimeException(e);
      }
    }

    @Override
    void append(String str) {
      int len = str.length();
      if (len > 0) {
        size += len;
        lastChar = str.charAt(len - 1);
        if (trackGzippedSize) {
          try {
            stream.write(str.getBytes());
          } catch (IOException e) {
            throw new RuntimeException(e);
          }
        }
      }
    }

    @Override
    char getLastChar() {
      return lastChar;
    }

    private int calcSize() {
      return size;
    }

    private int calcZippedSize() {
      if (trackGzippedSize) {
        try {
          stream.finish();
          stream.flush();
          stream.close();
          return output.size();
        } catch (IOException e) {
          throw new RuntimeException(e);
        }
      } else {
        return -1;
      }
    }
  }
}