third_party/WebKit/Source/core/timing/MemoryInfo.cpp

/*
 * Copyright (C) 2010 Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
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 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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#include "core/timing/MemoryInfo.h"

#include "core/frame/LocalFrame.h"
#include "core/frame/Settings.h"
#include "platform/RuntimeEnabledFeatures.h"
#include "wtf/CurrentTime.h"
#include "wtf/MathExtras.h"
#include "wtf/ThreadSpecific.h"
#include <limits>
#include <v8.h>

namespace blink {

static const double TwentyMinutesInSeconds = 20 * 60;

static void getHeapSize(HeapInfo& info) {
  v8::HeapStatistics heapStatistics;
  v8::Isolate::GetCurrent()->GetHeapStatistics(&heapStatistics);
  info.usedJSHeapSize = heapStatistics.used_heap_size();
  info.totalJSHeapSize = heapStatistics.total_physical_size();
  info.jsHeapSizeLimit = heapStatistics.heap_size_limit();
}

class HeapSizeCache {
  WTF_MAKE_NONCOPYABLE(HeapSizeCache);
  USING_FAST_MALLOC(HeapSizeCache);

 public:
  HeapSizeCache()
      : m_lastUpdateTime(monotonicallyIncreasingTime() -
                         TwentyMinutesInSeconds) {}

  void getCachedHeapSize(HeapInfo& info) {
    maybeUpdate();
    info = m_info;
  }

  static HeapSizeCache& forCurrentThread() {
    DEFINE_THREAD_SAFE_STATIC_LOCAL(ThreadSpecific<HeapSizeCache>,
                                    heapSizeCache,
                                    new ThreadSpecific<HeapSizeCache>);
    return *heapSizeCache;
  }

 private:
  void maybeUpdate() {
    // We rate-limit queries to once every twenty minutes to make it more
    // difficult for attackers to compare memory usage before and after some
    // event.
    double now = monotonicallyIncreasingTime();
    if (now - m_lastUpdateTime >= TwentyMinutesInSeconds) {
      update();
      m_lastUpdateTime = now;
    }
  }

  void update() {
    getHeapSize(m_info);
    m_info.usedJSHeapSize = quantizeMemorySize(m_info.usedJSHeapSize);
    m_info.totalJSHeapSize = quantizeMemorySize(m_info.totalJSHeapSize);
    m_info.jsHeapSizeLimit = quantizeMemorySize(m_info.jsHeapSizeLimit);
  }

  double m_lastUpdateTime;

  HeapInfo m_info;
};

// We quantize the sizes to make it more difficult for an attacker to see
// precise impact of operations on memory. The values are used for performance
// tuning, and hence don't need to be as refined when the value is large, so we
// threshold at a list of exponentially separated buckets.
size_t quantizeMemorySize(size_t size) {
  const int numberOfBuckets = 100;
  DEFINE_STATIC_LOCAL(Vector<size_t>, bucketSizeList, ());

  if (bucketSizeList.isEmpty()) {
    bucketSizeList.resize(numberOfBuckets);

    float sizeOfNextBucket = 10000000.0;  // First bucket size is roughly 10M.
    const float largestBucketSize = 4000000000.0;  // Roughly 4GB.
    // We scale with the Nth root of the ratio, so that we use all the bucktes.
    const float scalingFactor =
        exp(log(largestBucketSize / sizeOfNextBucket) / numberOfBuckets);

    size_t nextPowerOfTen =
        static_cast<size_t>(pow(10, floor(log10(sizeOfNextBucket)) + 1) + 0.5);
    size_t granularity = nextPowerOfTen / 1000;  // We want 3 signficant digits.

    for (int i = 0; i < numberOfBuckets; ++i) {
      size_t currentBucketSize = static_cast<size_t>(sizeOfNextBucket);
      bucketSizeList[i] = currentBucketSize - (currentBucketSize % granularity);

      sizeOfNextBucket *= scalingFactor;
      if (sizeOfNextBucket >= nextPowerOfTen) {
        if (std::numeric_limits<size_t>::max() / 10 <= nextPowerOfTen) {
          nextPowerOfTen = std::numeric_limits<size_t>::max();
        } else {
          nextPowerOfTen *= 10;
          granularity *= 10;
        }
      }

      // Watch out for overflow, if the range is too large for size_t.
      if (i > 0 && bucketSizeList[i] < bucketSizeList[i - 1])
        bucketSizeList[i] = std::numeric_limits<size_t>::max();
    }
  }

  for (int i = 0; i < numberOfBuckets; ++i) {
    if (size <= bucketSizeList[i])
      return bucketSizeList[i];
  }

  return bucketSizeList[numberOfBuckets - 1];
}

MemoryInfo::MemoryInfo() {
  if (RuntimeEnabledFeatures::preciseMemoryInfoEnabled())
    getHeapSize(m_info);
  else
    HeapSizeCache::forCurrentThread().getCachedHeapSize(m_info);
}

}  // namespace blink