text: // Copyright (c) 2012 The Chromium Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  // Histogram is an object that aggregates statistics, and can summarize them in
  // various forms, including ASCII graphical, HTML, and numerically (as a
  // vector of numbers corresponding to each of the aggregating buckets).
  // See header file for details and examples.
  
  #include "base/metrics/histogram.h"
  
  #include <inttypes.h>
  #include <limits.h>
  #include <math.h>
  
  #include <algorithm>
  #include <string>
  #include <utility>
  
  #include "base/compiler_specific.h"
  #include "base/debug/alias.h"
  #include "base/debug/crash_logging.h"
  #include "base/logging.h"
  #include "base/memory/ptr_util.h"
  #include "base/metrics/histogram_macros.h"
  #include "base/metrics/metrics_hashes.h"
  #include "base/metrics/persistent_histogram_allocator.h"
  #include "base/metrics/persistent_memory_allocator.h"
  #include "base/metrics/sample_vector.h"
  #include "base/metrics/statistics_recorder.h"
  #include "base/pickle.h"
  #include "base/strings/string_util.h"
  #include "base/strings/stringprintf.h"
  #include "base/synchronization/lock.h"
  #include "base/values.h"
  #include "build/build_config.h"
  
  namespace base {
  
  namespace {
  
  // A constant to be stored in the dummy field and later verified. This could
  // be either 32 or 64 bit but clang won't truncate the value without an error.
  // TODO(bcwhite): Remove this once crbug/736675 is fixed.
  #if defined(ARCH_CPU_64_BITS) && !defined(OS_NACL)
  constexpr uintptr_t kDummyValue = 0xFEEDC0DEDEADBEEF;
  #else
  constexpr uintptr_t kDummyValue = 0xDEADBEEF;
  #endif
  
  bool ReadHistogramArguments(PickleIterator* iter,
                              std::string* histogram_name,
                              int* flags,
                              int* declared_min,
                              int* declared_max,
                              uint32_t* bucket_count,
                              uint32_t* range_checksum) {
    if (!iter->ReadString(histogram_name) ||
        !iter->ReadInt(flags) ||
        !iter->ReadInt(declared_min) ||
        !iter->ReadInt(declared_max) ||
        !iter->ReadUInt32(bucket_count) ||
        !iter->ReadUInt32(range_checksum)) {
      DLOG(ERROR) << "Pickle error decoding Histogram: " << *histogram_name;
      return false;
    }
  
    // Since these fields may have come from an untrusted renderer, do additional
    // checks above and beyond those in Histogram::Initialize()
    if (*declared_max <= 0 ||
        *declared_min <= 0 ||
        *declared_max < *declared_min ||
        INT_MAX / sizeof(HistogramBase::Count) <= *bucket_count ||
        *bucket_count < 2) {
      DLOG(ERROR) << "Values error decoding Histogram: " << histogram_name;
      return false;
    }
  
    // We use the arguments to find or create the local version of the histogram
    // in this process, so we need to clear any IPC flag.
    *flags &= ~HistogramBase::kIPCSerializationSourceFlag;
  
    return true;
  }
  
  bool ValidateRangeChecksum(const HistogramBase& histogram,
                             uint32_t range_checksum) {
    const Histogram& casted_histogram =
        static_cast<const Histogram&>(histogram);
  
    return casted_histogram.bucket_ranges()->checksum() == range_checksum;
  }
  
  }  // namespace
  
  typedef HistogramBase::Count Count;
  typedef HistogramBase::Sample Sample;
  
  // static
  const uint32_t Histogram::kBucketCount_MAX = 16384u;
  
  class Histogram::Factory {
   public:
    Factory(const std::string& name,
            HistogramBase::Sample minimum,
            HistogramBase::Sample maximum,
            uint32_t bucket_count,
            int32_t flags)
      : Factory(name, HISTOGRAM, minimum, maximum, bucket_count, flags) {}
  
    // Create histogram based on construction parameters. Caller takes
    // ownership of the returned object.
    HistogramBase* Build();
  
   protected:
    Factory(const std::string& name,
            HistogramType histogram_type,
            HistogramBase::Sample minimum,
            HistogramBase::Sample maximum,
            uint32_t bucket_count,
            int32_t flags)
      : name_(name),
        histogram_type_(histogram_type),
        minimum_(minimum),
        maximum_(maximum),
        bucket_count_(bucket_count),
        flags_(flags) {}
  
    // Create a BucketRanges structure appropriate for this histogram.
    virtual BucketRanges* CreateRanges() {
      BucketRanges* ranges = new BucketRanges(bucket_count_ + 1);
      Histogram::InitializeBucketRanges(minimum_, maximum_, ranges);
      base::debug::Alias(&ranges);  // TODO(bcwhite): Remove after crbug/586622.
      return ranges;
    }
  
    // Allocate the correct Histogram object off the heap (in case persistent
    // memory is not available).
    virtual std::unique_ptr<HistogramBase> HeapAlloc(const BucketRanges* ranges) {
      return WrapUnique(new Histogram(name_, minimum_, maximum_, ranges));
    }
  
    // Perform any required datafill on the just-created histogram.  If
    // overridden, be sure to call the "super" version -- this method may not
    // always remain empty.
    virtual void FillHistogram(HistogramBase* histogram) {}
  
    // These values are protected (instead of private) because they need to
    // be accessible to methods of sub-classes in order to avoid passing
    // unnecessary parameters everywhere.
    const std::string& name_;
    const HistogramType histogram_type_;
    HistogramBase::Sample minimum_;
    HistogramBase::Sample maximum_;
    uint32_t bucket_count_;
    int32_t flags_;
  
   private:
    DISALLOW_COPY_AND_ASSIGN(Factory);
  };
  
  HistogramBase* Histogram::Factory::Build() {
    HistogramBase* histogram = StatisticsRecorder::FindHistogram(name_);
    if (!histogram) {
      // To avoid racy destruction at shutdown, the following will be leaked.
      const BucketRanges* created_ranges = CreateRanges();
      const BucketRanges* registered_ranges =
          StatisticsRecorder::RegisterOrDeleteDuplicateRanges(created_ranges);
  
      // In most cases, the bucket-count, minimum, and maximum values are known
      // when the code is written and so are passed in explicitly. In other
      // cases (such as with a CustomHistogram), they are calculated dynamically
      // at run-time. In the latter case, those ctor parameters are zero and
      // the results extracted from the result of CreateRanges().
      if (bucket_count_ == 0) {
        bucket_count_ = static_cast<uint32_t>(registered_ranges->bucket_count());
        minimum_ = registered_ranges->range(1);
        maximum_ = registered_ranges->range(bucket_count_ - 1);
      }
      DCHECK_EQ(minimum_, registered_ranges->range(1));
      DCHECK_EQ(maximum_, registered_ranges->range(bucket_count_ - 1));
  
      // Try to create the histogram using a "persistent" allocator. As of
      // 2016-02-25, the availability of such is controlled by a base::Feature
      // that is off by default. If the allocator doesn't exist or if
      // allocating from it fails, code below will allocate the histogram from
      // the process heap.
      PersistentHistogramAllocator::Reference histogram_ref = 0;
      std::unique_ptr<HistogramBase> tentative_histogram;
      PersistentHistogramAllocator* allocator = GlobalHistogramAllocator::Get();
      if (allocator) {
        tentative_histogram = allocator->AllocateHistogram(
            histogram_type_,
            name_,
            minimum_,
            maximum_,
            registered_ranges,
            flags_,
            &histogram_ref);
      }
  
      // Handle the case where no persistent allocator is present or the
      // persistent allocation fails (perhaps because it is full).
      if (!tentative_histogram) {
        DCHECK(!histogram_ref);  // Should never have been set.
        DCHECK(!allocator);  // Shouldn't have failed.
        flags_ &= ~HistogramBase::kIsPersistent;
        tentative_histogram = HeapAlloc(registered_ranges);
        tentative_histogram->SetFlags(flags_);
      }
  
      FillHistogram(tentative_histogram.get());
  
      // Register this histogram with the StatisticsRecorder. Keep a copy of
      // the pointer value to tell later whether the locally created histogram
      // was registered or deleted. The type is "void" because it could point
      // to released memory after the following line.
      const void* tentative_histogram_ptr = tentative_histogram.get();
      histogram = StatisticsRecorder::RegisterOrDeleteDuplicate(
          tentative_histogram.release());
  
      // Persistent histograms need some follow-up processing.
      if (histogram_ref) {
        allocator->FinalizeHistogram(histogram_ref,
                                     histogram == tentative_histogram_ptr);
      }
  
      // Update report on created histograms.
      ReportHistogramActivity(*histogram, HISTOGRAM_CREATED);
    } else {
      // Update report on lookup histograms.
      ReportHistogramActivity(*histogram, HISTOGRAM_LOOKUP);
    }
  
    CHECK_EQ(histogram_type_, histogram->GetHistogramType()) << name_;
    if (bucket_count_ != 0 &&
        !histogram->HasConstructionArguments(minimum_, maximum_, bucket_count_)) {
      // The construction arguments do not match the existing histogram.  This can
      // come about if an extension updates in the middle of a chrome run and has
      // changed one of them, or simply by bad code within Chrome itself.  We
      // return NULL here with the expectation that bad code in Chrome will crash
      // on dereference, but extension/Pepper APIs will guard against NULL and not
      // crash.
      DLOG(ERROR) << "Histogram " << name_ << " has bad construction arguments";
      return nullptr;
    }
    return histogram;
  }
  
  HistogramBase* Histogram::FactoryGet(const std::string& name,
                                       Sample minimum,
                                       Sample maximum,
                                       uint32_t bucket_count,
                                       int32_t flags) {
    bool valid_arguments =
        InspectConstructionArguments(name, &minimum, &maximum, &bucket_count);
    DCHECK(valid_arguments);
  
    return Factory(name, minimum, maximum, bucket_count, flags).Build();
  }
  
  HistogramBase* Histogram::FactoryTimeGet(const std::string& name,
                                           TimeDelta minimum,
                                           TimeDelta maximum,
                                           uint32_t bucket_count,
                                           int32_t flags) {
    return FactoryGet(name, static_cast<Sample>(minimum.InMilliseconds()),
                      static_cast<Sample>(maximum.InMilliseconds()), bucket_count,
                      flags);
  }
  
  HistogramBase* Histogram::FactoryGet(const char* name,
                                       Sample minimum,
                                       Sample maximum,
                                       uint32_t bucket_count,
                                       int32_t flags) {
    return FactoryGet(std::string(name), minimum, maximum, bucket_count, flags);
  }
  
  HistogramBase* Histogram::FactoryTimeGet(const char* name,
                                           TimeDelta minimum,
                                           TimeDelta maximum,
                                           uint32_t bucket_count,
                                           int32_t flags) {
    return FactoryTimeGet(std::string(name), minimum, maximum, bucket_count,
                          flags);
  }
  
  std::unique_ptr<HistogramBase> Histogram::PersistentCreate(
      const std::string& name,
      Sample minimum,
      Sample maximum,
      const BucketRanges* ranges,
      const DelayedPersistentAllocation& counts,
      const DelayedPersistentAllocation& logged_counts,
      HistogramSamples::Metadata* meta,
      HistogramSamples::Metadata* logged_meta) {
    return WrapUnique(new Histogram(name, minimum, maximum, ranges, counts,
                                    logged_counts, meta, logged_meta));
  }
  
  // Calculate what range of values are held in each bucket.
  // We have to be careful that we don't pick a ratio between starting points in
  // consecutive buckets that is sooo small, that the integer bounds are the same
  // (effectively making one bucket get no values).  We need to avoid:
  //   ranges(i) == ranges(i + 1)
  // To avoid that, we just do a fine-grained bucket width as far as we need to
  // until we get a ratio that moves us along at least 2 units at a time.  From
  // that bucket onward we do use the exponential growth of buckets.
  //
  // static
  void Histogram::InitializeBucketRanges(Sample minimum,
                                         Sample maximum,
                                         BucketRanges* ranges) {
    double log_max = log(static_cast<double>(maximum));
    double log_ratio;
    double log_next;
    size_t bucket_index = 1;
    Sample current = minimum;
    ranges->set_range(bucket_index, current);
    size_t bucket_count = ranges->bucket_count();
    while (bucket_count > ++bucket_index) {
      double log_current;
      log_current = log(static_cast<double>(current));
      // Calculate the count'th root of the range.
      log_ratio = (log_max - log_current) / (bucket_count - bucket_index);
      // See where the next bucket would start.
      log_next = log_current + log_ratio;
      Sample next;
      next = static_cast<int>(floor(exp(log_next) + 0.5));
      if (next > current)
        current = next;
      else
        ++current;  // Just do a narrow bucket, and keep trying.
      ranges->set_range(bucket_index, current);
    }
    ranges->set_range(ranges->bucket_count(), HistogramBase::kSampleType_MAX);
    ranges->ResetChecksum();
  }
  
  // static
  const int Histogram::kCommonRaceBasedCountMismatch = 5;
  
  uint32_t Histogram::FindCorruption(const HistogramSamples& samples) const {
    int inconsistencies = NO_INCONSISTENCIES;
    Sample previous_range = -1;  // Bottom range is always 0.
    for (uint32_t index = 0; index < bucket_count(); ++index) {
      int new_range = ranges(index);
      if (previous_range >= new_range)
        inconsistencies |= BUCKET_ORDER_ERROR;
      previous_range = new_range;
    }
  
    if (!bucket_ranges()->HasValidChecksum())
      inconsistencies |= RANGE_CHECKSUM_ERROR;
  
    int64_t delta64 = samples.redundant_count() - samples.TotalCount();
    if (delta64 != 0) {
      int delta = static_cast<int>(delta64);
      if (delta != delta64)
        delta = INT_MAX;  // Flag all giant errors as INT_MAX.
      if (delta > 0) {
        if (delta > kCommonRaceBasedCountMismatch)
          inconsistencies |= COUNT_HIGH_ERROR;
      } else {
        DCHECK_GT(0, delta);
        if (-delta > kCommonRaceBasedCountMismatch)
          inconsistencies |= COUNT_LOW_ERROR;
      }
    }
    return inconsistencies;
  }
  
  const BucketRanges* Histogram::bucket_ranges() const {
    return unlogged_samples_->bucket_ranges();
  }
  
  Sample Histogram::declared_min() const {
    const BucketRanges* ranges = bucket_ranges();
    if (ranges->bucket_count() < 2)
      return -1;
    return ranges->range(1);
  }
  
  Sample Histogram::declared_max() const {
    const BucketRanges* ranges = bucket_ranges();
    if (ranges->bucket_count() < 2)
      return -1;
    return ranges->range(ranges->bucket_count() - 1);
  }
  
  Sample Histogram::ranges(uint32_t i) const {
    return bucket_ranges()->range(i);
  }
  
  uint32_t Histogram::bucket_count() const {
    return static_cast<uint32_t>(bucket_ranges()->bucket_count());
  }
  
  // static
  bool Histogram::InspectConstructionArguments(const std::string& name,
                                               Sample* minimum,
                                               Sample* maximum,
                                               uint32_t* bucket_count) {
    // Defensive code for backward compatibility.
    if (*minimum < 1) {
      DVLOG(1) << "Histogram: " << name << " has bad minimum: " << *minimum;
      *minimum = 1;
    }
    if (*maximum >= kSampleType_MAX) {
      DVLOG(1) << "Histogram: " << name << " has bad maximum: " << *maximum;
      *maximum = kSampleType_MAX - 1;
    }
    if (*bucket_count >= kBucketCount_MAX) {
      DVLOG(1) << "Histogram: " << name << " has bad bucket_count: "
               << *bucket_count;
      *bucket_count = kBucketCount_MAX - 1;
    }
  
    bool check_okay = true;
  
    if (*minimum > *maximum) {
      check_okay = false;
      std::swap(*minimum, *maximum);
    }
    if (*maximum == *minimum) {
      check_okay = false;
      *maximum = *minimum + 1;
    }
    if (*bucket_count < 3) {
      check_okay = false;
      *bucket_count = 3;
    }
    // Very high bucket counts are wasteful. Use a sparse histogram instead.
    // Value of 10002 equals a user-supplied value of 10k + 2 overflow buckets.
    constexpr uint32_t kMaxBucketCount = 10002;
    if (*bucket_count > kMaxBucketCount) {
      check_okay = false;
      *bucket_count = kMaxBucketCount;
    }
    if (*bucket_count > static_cast<uint32_t>(*maximum - *minimum + 2)) {
      check_okay = false;
      *bucket_count = static_cast<uint32_t>(*maximum - *minimum + 2);
    }
  
    if (!check_okay) {
      UMA_HISTOGRAM_SPARSE_SLOWLY("Histogram.BadConstructionArguments",
                                  static_cast<Sample>(HashMetricName(name)));
    }
  
    return check_okay;
  }
  
  uint64_t Histogram::name_hash() const {
    return unlogged_samples_->id();
  }
  
  HistogramType Histogram::GetHistogramType() const {
    return HISTOGRAM;
  }
  
  bool Histogram::HasConstructionArguments(Sample expected_minimum,
                                           Sample expected_maximum,
                                           uint32_t expected_bucket_count) const {
    return (expected_bucket_count == bucket_count() &&
            expected_minimum == declared_min() &&
            expected_maximum == declared_max());
  }
  
  void Histogram::Add(int value) {
    AddCount(value, 1);
  }
  
  void Histogram::AddCount(int value, int count) {
    DCHECK_EQ(0, ranges(0));
    DCHECK_EQ(kSampleType_MAX, ranges(bucket_count()));
  
    if (value > kSampleType_MAX - 1)
      value = kSampleType_MAX - 1;
    if (value < 0)
      value = 0;
    if (count <= 0) {
      NOTREACHED();
      return;
    }
    unlogged_samples_->Accumulate(value, count);
  
    FindAndRunCallback(value);
  }
  
  std::unique_ptr<HistogramSamples> Histogram::SnapshotSamples() const {
    return SnapshotAllSamples();
  }
  
  std::unique_ptr<HistogramSamples> Histogram::SnapshotDelta() {
  #if DCHECK_IS_ON()
    DCHECK(!final_delta_created_);
  #endif
  
    // The code below has subtle thread-safety guarantees! All changes to
    // the underlying SampleVectors use atomic integer operations, which guarantee
    // eventual consistency, but do not guarantee full synchronization between
    // different entries in the SampleVector. In particular, this means that
    // concurrent updates to the histogram might result in the reported sum not
    // matching the individual bucket counts; or there being some buckets that are
    // logically updated "together", but end up being only partially updated when
    // a snapshot is captured. Note that this is why it's important to subtract
    // exactly the snapshotted unlogged samples, rather than simply resetting the
    // vector: this way, the next snapshot will include any concurrent updates
    // missed by the current snapshot.
  
    std::unique_ptr<HistogramSamples> snapshot = SnapshotUnloggedSamples();
    unlogged_samples_->Subtract(*snapshot);
    logged_samples_->Add(*snapshot);
  
    return snapshot;
  }
  
  std::unique_ptr<HistogramSamples> Histogram::SnapshotFinalDelta() const {
  #if DCHECK_IS_ON()
    DCHECK(!final_delta_created_);
    final_delta_created_ = true;
  #endif
  
    return SnapshotUnloggedSamples();
  }
  
  void Histogram::AddSamples(const HistogramSamples& samples) {
    unlogged_samples_->Add(samples);
  }
  
  bool Histogram::AddSamplesFromPickle(PickleIterator* iter) {
    return unlogged_samples_->AddFromPickle(iter);
  }
  
  // The following methods provide a graphical histogram display.
  void Histogram::WriteHTMLGraph(std::string* output) const {
    // TBD(jar) Write a nice HTML bar chart, with divs an mouse-overs etc.
    output->append("<PRE>");
    WriteAsciiImpl(true, "<br>", output);
    output->append("</PRE>");
  }
  
  void Histogram::WriteAscii(std::string* output) const {
    WriteAsciiImpl(true, "\n", output);
  }
  
  bool Histogram::ValidateHistogramContents(bool crash_if_invalid,
                                            int corrupted_count) const {
    enum Fields : int {
      kUnloggedBucketRangesField,
      kUnloggedSamplesField,
      kLoggedSamplesField,
      kIdField,
      kHistogramNameField,
      kFlagsField,
      kLoggedBucketRangesField,
      kDummyField,
    };
  
    uint32_t bad_fields = 0;
    if (!unlogged_samples_)
      bad_fields |= 1 << kUnloggedSamplesField;
    else if (!unlogged_samples_->bucket_ranges())
      bad_fields |= 1 << kUnloggedBucketRangesField;
    if (!logged_samples_)
      bad_fields |= 1 << kLoggedSamplesField;
    else if (!logged_samples_->bucket_ranges())
      bad_fields |= 1 << kLoggedBucketRangesField;
    else if (logged_samples_->id() == 0)
      bad_fields |= 1 << kIdField;
    else if (HashMetricName(histogram_name()) != logged_samples_->id())
      bad_fields |= 1 << kHistogramNameField;
    if (flags() == 0)
      bad_fields |= 1 << kFlagsField;
    if (dummy_ != kDummyValue)
      bad_fields |= 1 << kDummyField;
  
    const bool is_valid = (bad_fields & ~(1 << kFlagsField)) == 0;
    if (is_valid || !crash_if_invalid)
      return is_valid;
  
    // Abort if a problem is found (except "flags", which could legally be zero).
    const std::string debug_string =
        base::StringPrintf("%s/%" PRIu32 "/%d", histogram_name().c_str(),
                           bad_fields, corrupted_count);
  #if !defined(OS_NACL)
    // Temporary for https://crbug.com/736675.
    base::debug::ScopedCrashKey crash_key("bad_histogram", debug_string);
  #endif
    CHECK(false) << debug_string;
    debug::Alias(&bad_fields);
    return false;
  }
  
  bool Histogram::SerializeInfoImpl(Pickle* pickle) const {
    DCHECK(bucket_ranges()->HasValidChecksum());
    return pickle->WriteString(histogram_name()) &&
        pickle->WriteInt(flags()) &&
        pickle->WriteInt(declared_min()) &&
        pickle->WriteInt(declared_max()) &&
        pickle->WriteUInt32(bucket_count()) &&
        pickle->WriteUInt32(bucket_ranges()->checksum());
  }
  
  // TODO(bcwhite): Remove minimum/maximum parameters from here and call chain.
  Histogram::Histogram(const std::string& name,
                       Sample minimum,
                       Sample maximum,
                       const BucketRanges* ranges)
      : HistogramBase(name), dummy_(kDummyValue) {
    // TODO(bcwhite): Make this a DCHECK once crbug/734049 is resolved.
    CHECK(ranges) << name << ": " << minimum << "-" << maximum;
    unlogged_samples_.reset(new SampleVector(HashMetricName(name), ranges));
    logged_samples_.reset(new SampleVector(unlogged_samples_->id(), ranges));
  }
  
  Histogram::Histogram(const std::string& name,
                       Sample minimum,
                       Sample maximum,
                       const BucketRanges* ranges,
                       const DelayedPersistentAllocation& counts,
                       const DelayedPersistentAllocation& logged_counts,
                       HistogramSamples::Metadata* meta,
                       HistogramSamples::Metadata* logged_meta)
      : HistogramBase(name), dummy_(kDummyValue) {
    // TODO(bcwhite): Make this a DCHECK once crbug/734049 is resolved.
    CHECK(ranges) << name << ": " << minimum << "-" << maximum;
    unlogged_samples_.reset(
        new PersistentSampleVector(HashMetricName(name), ranges, meta, counts));
    logged_samples_.reset(new PersistentSampleVector(
        unlogged_samples_->id(), ranges, logged_meta, logged_counts));
  }
  
  Histogram::~Histogram() {
  }
  
  bool Histogram::PrintEmptyBucket(uint32_t index) const {
    return true;
  }
  
  // Use the actual bucket widths (like a linear histogram) until the widths get
  // over some transition value, and then use that transition width.  Exponentials
  // get so big so fast (and we don't expect to see a lot of entries in the large
  // buckets), so we need this to make it possible to see what is going on and
  // not have 0-graphical-height buckets.
  double Histogram::GetBucketSize(Count current, uint32_t i) const {
    DCHECK_GT(ranges(i + 1), ranges(i));
    static const double kTransitionWidth = 5;
    double denominator = ranges(i + 1) - ranges(i);
    if (denominator > kTransitionWidth)
      denominator = kTransitionWidth;  // Stop trying to normalize.
    return current/denominator;
  }
  
  const std::string Histogram::GetAsciiBucketRange(uint32_t i) const {
    return GetSimpleAsciiBucketRange(ranges(i));
  }
  
  //------------------------------------------------------------------------------
  // Private methods
  
  // static
  HistogramBase* Histogram::DeserializeInfoImpl(PickleIterator* iter) {
    std::string histogram_name;
    int flags;
    int declared_min;
    int declared_max;
    uint32_t bucket_count;
    uint32_t range_checksum;
  
    if (!ReadHistogramArguments(iter, &histogram_name, &flags, &declared_min,
                                &declared_max, &bucket_count, &range_checksum)) {
      return nullptr;
    }
  
    // Find or create the local version of the histogram in this process.
    HistogramBase* histogram = Histogram::FactoryGet(
        histogram_name, declared_min, declared_max, bucket_count, flags);
    if (!histogram)
      return nullptr;
  
    // The serialized histogram might be corrupted.
    if (!ValidateRangeChecksum(*histogram, range_checksum))
      return nullptr;
  
    return histogram;
  }
  
  std::unique_ptr<SampleVector> Histogram::SnapshotAllSamples() const {
    std::unique_ptr<SampleVector> samples = SnapshotUnloggedSamples();
    samples->Add(*logged_samples_);
    return samples;
  }
  
  std::unique_ptr<SampleVector> Histogram::SnapshotUnloggedSamples() const {
    // TODO(bcwhite): Remove these CHECKs once crbug/734049 is resolved.
    HistogramSamples* unlogged = unlogged_samples_.get();
    CHECK(unlogged_samples_);
    CHECK(unlogged_samples_->id());
    CHECK(bucket_ranges());
    std::unique_ptr<SampleVector> samples(
        new SampleVector(unlogged_samples_->id(), bucket_ranges()));
    samples->Add(*unlogged_samples_);
    debug::Alias(&unlogged);
    return samples;
  }
  
  void Histogram::WriteAsciiImpl(bool graph_it,
                                 const std::string& newline,
                                 std::string* output) const {
    // Get local (stack) copies of all effectively volatile class data so that we
    // are consistent across our output activities.
    std::unique_ptr<SampleVector> snapshot = SnapshotAllSamples();
    Count sample_count = snapshot->TotalCount();
  
    WriteAsciiHeader(*snapshot, sample_count, output);
    output->append(newline);
  
    // Prepare to normalize graphical rendering of bucket contents.
    double max_size = 0;
    if (graph_it)
      max_size = GetPeakBucketSize(*snapshot);
  
    // Calculate space needed to print bucket range numbers.  Leave room to print
    // nearly the largest bucket range without sliding over the histogram.
    uint32_t largest_non_empty_bucket = bucket_count() - 1;
    while (0 == snapshot->GetCountAtIndex(largest_non_empty_bucket)) {
      if (0 == largest_non_empty_bucket)
        break;  // All buckets are empty.
      --largest_non_empty_bucket;
    }
  
    // Calculate largest print width needed for any of our bucket range displays.
    size_t print_width = 1;
    for (uint32_t i = 0; i < bucket_count(); ++i) {
      if (snapshot->GetCountAtIndex(i)) {
        size_t width = GetAsciiBucketRange(i).size() + 1;
        if (width > print_width)
          print_width = width;
      }
    }
  
    int64_t remaining = sample_count;
    int64_t past = 0;
    // Output the actual histogram graph.
    for (uint32_t i = 0; i < bucket_count(); ++i) {
      Count current = snapshot->GetCountAtIndex(i);
      if (!current && !PrintEmptyBucket(i))
        continue;
      remaining -= current;
      std::string range = GetAsciiBucketRange(i);
      output->append(range);
      for (size_t j = 0; range.size() + j < print_width + 1; ++j)
        output->push_back(' ');
      if (0 == current && i < bucket_count() - 1 &&
          0 == snapshot->GetCountAtIndex(i + 1)) {
        while (i < bucket_count() - 1 &&
               0 == snapshot->GetCountAtIndex(i + 1)) {
          ++i;
        }
        output->append("... ");
        output->append(newline);
        continue;  // No reason to plot emptiness.
      }
      double current_size = GetBucketSize(current, i);
      if (graph_it)
        WriteAsciiBucketGraph(current_size, max_size, output);
      WriteAsciiBucketContext(past, current, remaining, i, output);
      output->append(newline);
      past += current;
    }
    DCHECK_EQ(sample_count, past);
  }
  
  double Histogram::GetPeakBucketSize(const SampleVectorBase& samples) const {
    double max = 0;
    for (uint32_t i = 0; i < bucket_count() ; ++i) {
      double current_size = GetBucketSize(samples.GetCountAtIndex(i), i);
      if (current_size > max)
        max = current_size;
    }
    return max;
  }
  
  void Histogram::WriteAsciiHeader(const SampleVectorBase& samples,
                                   Count sample_count,
                                   std::string* output) const {
    StringAppendF(output,
                  "Histogram: %s recorded %d samples",
                  histogram_name().c_str(),
                  sample_count);
    if (sample_count == 0) {
      DCHECK_EQ(samples.sum(), 0);
    } else {
      double mean = static_cast<float>(samples.sum()) / sample_count;
      StringAppendF(output, ", mean = %.1f", mean);
    }
    if (flags())
      StringAppendF(output, " (flags = 0x%x)", flags());
  }
  
  void Histogram::WriteAsciiBucketContext(const int64_t past,
                                          const Count current,
                                          const int64_t remaining,
                                          const uint32_t i,
                                          std::string* output) const {
    double scaled_sum = (past + current + remaining) / 100.0;
    WriteAsciiBucketValue(current, scaled_sum, output);
    if (0 < i) {
      double percentage = past / scaled_sum;
      StringAppendF(output, " {%3.1f%%}", percentage);
    }
  }
  
  void Histogram::GetParameters(DictionaryValue* params) const {
    params->SetString("type", HistogramTypeToString(GetHistogramType()));
    params->SetInteger("min", declared_min());
    params->SetInteger("max", declared_max());
    params->SetInteger("bucket_count", static_cast<int>(bucket_count()));
  }
  
  void Histogram::GetCountAndBucketData(Count* count,
                                        int64_t* sum,
                                        ListValue* buckets) const {
    std::unique_ptr<SampleVector> snapshot = SnapshotAllSamples();
    *count = snapshot->TotalCount();
    *sum = snapshot->sum();
    uint32_t index = 0;
    for (uint32_t i = 0; i < bucket_count(); ++i) {
      Sample count_at_index = snapshot->GetCountAtIndex(i);
      if (count_at_index > 0) {
        std::unique_ptr<DictionaryValue> bucket_value(new DictionaryValue());
        bucket_value->SetInteger("low", ranges(i));
        if (i != bucket_count() - 1)
          bucket_value->SetInteger("high", ranges(i + 1));
        bucket_value->SetInteger("count", count_at_index);
        buckets->Set(index, std::move(bucket_value));
        ++index;
      }
    }
  }
  
  //------------------------------------------------------------------------------
  // LinearHistogram: This histogram uses a traditional set of evenly spaced
  // buckets.
  //------------------------------------------------------------------------------
  
  class LinearHistogram::Factory : public Histogram::Factory {
   public:
    Factory(const std::string& name,
            HistogramBase::Sample minimum,
            HistogramBase::Sample maximum,
            uint32_t bucket_count,
            int32_t flags,
            const DescriptionPair* descriptions)
      : Histogram::Factory(name, LINEAR_HISTOGRAM, minimum, maximum,
                           bucket_count, flags) {
      descriptions_ = descriptions;
    }
  
   protected:
    BucketRanges* CreateRanges() override {
      BucketRanges* ranges = new BucketRanges(bucket_count_ + 1);
      LinearHistogram::InitializeBucketRanges(minimum_, maximum_, ranges);
      base::debug::Alias(&ranges);  // TODO(bcwhite): Remove after crbug/586622.
      return ranges;
    }
  
    std::unique_ptr<HistogramBase> HeapAlloc(
        const BucketRanges* ranges) override {
      return WrapUnique(new LinearHistogram(name_, minimum_, maximum_, ranges));
    }
  
    void FillHistogram(HistogramBase* base_histogram) override {
      Histogram::Factory::FillHistogram(base_histogram);
      LinearHistogram* histogram = static_cast<LinearHistogram*>(base_histogram);
      // Set range descriptions.
      if (descriptions_) {
        for (int i = 0; descriptions_[i].description; ++i) {
          histogram->bucket_description_[descriptions_[i].sample] =
              descriptions_[i].description;
        }
      }
    }
  
   private:
    const DescriptionPair* descriptions_;
  
    DISALLOW_COPY_AND_ASSIGN(Factory);
  };
  
  LinearHistogram::~LinearHistogram() {}
  
  HistogramBase* LinearHistogram::FactoryGet(const std::string& name,
                                             Sample minimum,
                                             Sample maximum,
                                             uint32_t bucket_count,
                                             int32_t flags) {
    return FactoryGetWithRangeDescription(name, minimum, maximum, bucket_count,
                                          flags, nullptr);
  }
  
  HistogramBase* LinearHistogram::FactoryTimeGet(const std::string& name,
                                                 TimeDelta minimum,
                                                 TimeDelta maximum,
                                                 uint32_t bucket_count,
                                                 int32_t flags) {
    return FactoryGet(name, static_cast<Sample>(minimum.InMilliseconds()),
                      static_cast<Sample>(maximum.InMilliseconds()), bucket_count,
                      flags);
  }
  
  HistogramBase* LinearHistogram::FactoryGet(const char* name,
                                             Sample minimum,
                                             Sample maximum,
                                             uint32_t bucket_count,
                                             int32_t flags) {
    return FactoryGet(std::string(name), minimum, maximum, bucket_count, flags);
  }
  
  HistogramBase* LinearHistogram::FactoryTimeGet(const char* name,
                                                 TimeDelta minimum,
                                                 TimeDelta maximum,
                                                 uint32_t bucket_count,
                                                 int32_t flags) {
    return FactoryTimeGet(std::string(name),  minimum, maximum, bucket_count,
                          flags);
  }
  
  std::unique_ptr<HistogramBase> LinearHistogram::PersistentCreate(
      const std::string& name,
      Sample minimum,
      Sample maximum,
      const BucketRanges* ranges,
      const DelayedPersistentAllocation& counts,
      const DelayedPersistentAllocation& logged_counts,
      HistogramSamples::Metadata* meta,
      HistogramSamples::Metadata* logged_meta) {
    return WrapUnique(new LinearHistogram(name, minimum, maximum, ranges, counts,
                                          logged_counts, meta, logged_meta));
  }
  
  HistogramBase* LinearHistogram::FactoryGetWithRangeDescription(
      const std::string& name,
      Sample minimum,
      Sample maximum,
      uint32_t bucket_count,
      int32_t flags,
      const DescriptionPair descriptions[]) {
    bool valid_arguments = Histogram::InspectConstructionArguments(
        name, &minimum, &maximum, &bucket_count);
    DCHECK(valid_arguments);
  
    return Factory(name, minimum, maximum, bucket_count, flags, descriptions)
        .Build();
  }
  
  HistogramType LinearHistogram::GetHistogramType() const {
    return LINEAR_HISTOGRAM;
  }
  
  LinearHistogram::LinearHistogram(const std::string& name,
                                   Sample minimum,
                                   Sample maximum,
                                   const BucketRanges* ranges)
      : Histogram(name, minimum, maximum, ranges) {
  }
  
  LinearHistogram::LinearHistogram(
      const std::string& name,
      Sample minimum,
      Sample maximum,
      const BucketRanges* ranges,
      const DelayedPersistentAllocation& counts,
      const DelayedPersistentAllocation& logged_counts,
      HistogramSamples::Metadata* meta,
      HistogramSamples::Metadata* logged_meta)
      : Histogram(name,
                  minimum,
                  maximum,
                  ranges,
                  counts,
                  logged_counts,
                  meta,
                  logged_meta) {}
  
  double LinearHistogram::GetBucketSize(Count current, uint32_t i) const {
    DCHECK_GT(ranges(i + 1), ranges(i));
    // Adjacent buckets with different widths would have "surprisingly" many (few)
    // samples in a histogram if we didn't normalize this way.
    double denominator = ranges(i + 1) - ranges(i);
    return current/denominator;
  }
  
  const std::string LinearHistogram::GetAsciiBucketRange(uint32_t i) const {
    int range = ranges(i);
    BucketDescriptionMap::const_iterator it = bucket_description_.find(range);
    if (it == bucket_description_.end())
      return Histogram::GetAsciiBucketRange(i);
    return it->second;
  }
  
  bool LinearHistogram::PrintEmptyBucket(uint32_t index) const {
    return bucket_description_.find(ranges(index)) == bucket_description_.end();
  }
  
  // static
  void LinearHistogram::InitializeBucketRanges(Sample minimum,
                                               Sample maximum,
                                               BucketRanges* ranges) {
    double min = minimum;
    double max = maximum;
    size_t bucket_count = ranges->bucket_count();
    for (size_t i = 1; i < bucket_count; ++i) {
      double linear_range =
          (min * (bucket_count - 1 - i) + max * (i - 1)) / (bucket_count - 2);
      ranges->set_range(i, static_cast<Sample>(linear_range + 0.5));
      // TODO(bcwhite): Remove once crbug/586622 is fixed.
      base::debug::Alias(&linear_range);
    }
    ranges->set_range(ranges->bucket_count(), HistogramBase::kSampleType_MAX);
    ranges->ResetChecksum();
  }
  
  // static
  HistogramBase* LinearHistogram::DeserializeInfoImpl(PickleIterator* iter) {
    std::string histogram_name;
    int flags;
    int declared_min;
    int declared_max;
    uint32_t bucket_count;
    uint32_t range_checksum;
  
    if (!ReadHistogramArguments(iter, &histogram_name, &flags, &declared_min,
                                &declared_max, &bucket_count, &range_checksum)) {
      return nullptr;
    }
  
    HistogramBase* histogram = LinearHistogram::FactoryGet(
        histogram_name, declared_min, declared_max, bucket_count, flags);
    if (!ValidateRangeChecksum(*histogram, range_checksum)) {
      // The serialized histogram might be corrupted.
      return nullptr;
    }
    return histogram;
  }
  
  //------------------------------------------------------------------------------
  // This section provides implementation for BooleanHistogram.
  //------------------------------------------------------------------------------
  
  class BooleanHistogram::Factory : public Histogram::Factory {
   public:
    Factory(const std::string& name, int32_t flags)
      : Histogram::Factory(name, BOOLEAN_HISTOGRAM, 1, 2, 3, flags) {}
  
   protected:
    BucketRanges* CreateRanges() override {
      BucketRanges* ranges = new BucketRanges(3 + 1);
      LinearHistogram::InitializeBucketRanges(1, 2, ranges);
      base::debug::Alias(&ranges);  // TODO(bcwhite): Remove after crbug/586622.
      return ranges;
    }
  
    std::unique_ptr<HistogramBase> HeapAlloc(
        const BucketRanges* ranges) override {
      return WrapUnique(new BooleanHistogram(name_, ranges));
    }
  
   private:
    DISALLOW_COPY_AND_ASSIGN(Factory);
  };
  
  HistogramBase* BooleanHistogram::FactoryGet(const std::string& name,
                                              int32_t flags) {
    return Factory(name, flags).Build();
  }
  
  HistogramBase* BooleanHistogram::FactoryGet(const char* name, int32_t flags) {
    return FactoryGet(std::string(name), flags);
  }
  
  std::unique_ptr<HistogramBase> BooleanHistogram::PersistentCreate(
      const std::string& name,
      const BucketRanges* ranges,
      const DelayedPersistentAllocation& counts,
      const DelayedPersistentAllocation& logged_counts,
      HistogramSamples::Metadata* meta,
      HistogramSamples::Metadata* logged_meta) {
    return WrapUnique(new BooleanHistogram(name, ranges, counts, logged_counts,
                                           meta, logged_meta));
  }
  
  HistogramType BooleanHistogram::GetHistogramType() const {
    return BOOLEAN_HISTOGRAM;
  }
  
  BooleanHistogram::BooleanHistogram(const std::string& name,
                                     const BucketRanges* ranges)
      : LinearHistogram(name, 1, 2, ranges) {}
  
  BooleanHistogram::BooleanHistogram(
      const std::string& name,
      const BucketRanges* ranges,
      const DelayedPersistentAllocation& counts,
      const DelayedPersistentAllocation& logged_counts,
      HistogramSamples::Metadata* meta,
      HistogramSamples::Metadata* logged_meta)
      : LinearHistogram(name,
                        1,
                        2,
                        ranges,
                        counts,
                        logged_counts,
                        meta,
                        logged_meta) {}
  
  HistogramBase* BooleanHistogram::DeserializeInfoImpl(PickleIterator* iter) {
    std::string histogram_name;
    int flags;
    int declared_min;
    int declared_max;
    uint32_t bucket_count;
    uint32_t range_checksum;
  
    if (!ReadHistogramArguments(iter, &histogram_name, &flags, &declared_min,
                                &declared_max, &bucket_count, &range_checksum)) {
      return nullptr;
    }
  
    HistogramBase* histogram = BooleanHistogram::FactoryGet(
        histogram_name, flags);
    if (!ValidateRangeChecksum(*histogram, range_checksum)) {
      // The serialized histogram might be corrupted.
      return nullptr;
    }
    return histogram;
  }
  
  //------------------------------------------------------------------------------
  // CustomHistogram:
  //------------------------------------------------------------------------------
  
  class CustomHistogram::Factory : public Histogram::Factory {
   public:
    Factory(const std::string& name,
            const std::vector<Sample>* custom_ranges,
            int32_t flags)
      : Histogram::Factory(name, CUSTOM_HISTOGRAM, 0, 0, 0, flags) {
      custom_ranges_ = custom_ranges;
    }
  
   protected:
    BucketRanges* CreateRanges() override {
      // Remove the duplicates in the custom ranges array.
      std::vector<int> ranges = *custom_ranges_;
      ranges.push_back(0);  // Ensure we have a zero value.
      ranges.push_back(HistogramBase::kSampleType_MAX);
      std::sort(ranges.begin(), ranges.end());
      ranges.erase(std::unique(ranges.begin(), ranges.end()), ranges.end());
  
      BucketRanges* bucket_ranges = new BucketRanges(ranges.size());
      for (uint32_t i = 0; i < ranges.size(); i++) {
        bucket_ranges->set_range(i, ranges[i]);
      }
      bucket_ranges->ResetChecksum();
      return bucket_ranges;
    }
  
    std::unique_ptr<HistogramBase> HeapAlloc(
        const BucketRanges* ranges) override {
      return WrapUnique(new CustomHistogram(name_, ranges));
    }
  
   private:
    const std::vector<Sample>* custom_ranges_;
  
    DISALLOW_COPY_AND_ASSIGN(Factory);
  };
  
  HistogramBase* CustomHistogram::FactoryGet(
      const std::string& name,
      const std::vector<Sample>& custom_ranges,
      int32_t flags) {
    CHECK(ValidateCustomRanges(custom_ranges));
  
    return Factory(name, &custom_ranges, flags).Build();
  }
  
  HistogramBase* CustomHistogram::FactoryGet(
      const char* name,
      const std::vector<Sample>& custom_ranges,
      int32_t flags) {
    return FactoryGet(std::string(name), custom_ranges, flags);
  }
  
  std::unique_ptr<HistogramBase> CustomHistogram::PersistentCreate(
      const std::string& name,
      const BucketRanges* ranges,
      const DelayedPersistentAllocation& counts,
      const DelayedPersistentAllocation& logged_counts,
      HistogramSamples::Metadata* meta,
      HistogramSamples::Metadata* logged_meta) {
    return WrapUnique(new CustomHistogram(name, ranges, counts, logged_counts,
                                          meta, logged_meta));
  }
  
  HistogramType CustomHistogram::GetHistogramType() const {
    return CUSTOM_HISTOGRAM;
  }
  
  // static
  std::vector<Sample> CustomHistogram::ArrayToCustomRanges(
      const Sample* values, uint32_t num_values) {
    std::vector<Sample> all_values;
    for (uint32_t i = 0; i < num_values; ++i) {
      Sample value = values[i];
      all_values.push_back(value);
  
      // Ensure that a guard bucket is added. If we end up with duplicate
      // values, FactoryGet will take care of removing them.
      all_values.push_back(value + 1);
    }
    return all_values;
  }
  
  CustomHistogram::CustomHistogram(const std::string& name,
                                   const BucketRanges* ranges)
      : Histogram(name,
                  ranges->range(1),
                  ranges->range(ranges->bucket_count() - 1),
                  ranges) {}
  
  CustomHistogram::CustomHistogram(
      const std::string& name,
      const BucketRanges* ranges,
      const DelayedPersistentAllocation& counts,
      const DelayedPersistentAllocation& logged_counts,
      HistogramSamples::Metadata* meta,
      HistogramSamples::Metadata* logged_meta)
      : Histogram(name,
                  ranges->range(1),
                  ranges->range(ranges->bucket_count() - 1),
                  ranges,
                  counts,
                  logged_counts,
                  meta,
                  logged_meta) {}
  
  bool CustomHistogram::SerializeInfoImpl(Pickle* pickle) const {
    if (!Histogram::SerializeInfoImpl(pickle))
      return false;
  
    // Serialize ranges. First and last ranges are alwasy 0 and INT_MAX, so don't
    // write them.
    for (uint32_t i = 1; i < bucket_ranges()->bucket_count(); ++i) {
      if (!pickle->WriteInt(bucket_ranges()->range(i)))
        return false;
    }
    return true;
  }
  
  double CustomHistogram::GetBucketSize(Count current, uint32_t i) const {
    // If this is a histogram of enum values, normalizing the bucket count
    // by the bucket range is not helpful, so just return the bucket count.
    return current;
  }
  
  // static
  HistogramBase* CustomHistogram::DeserializeInfoImpl(PickleIterator* iter) {
    std::string histogram_name;
    int flags;
    int declared_min;
    int declared_max;
    uint32_t bucket_count;
    uint32_t range_checksum;
  
    if (!ReadHistogramArguments(iter, &histogram_name, &flags, &declared_min,
                                &declared_max, &bucket_count, &range_checksum)) {
      return nullptr;
    }
  
    // First and last ranges are not serialized.
    std::vector<Sample> sample_ranges(bucket_count - 1);
  
    for (uint32_t i = 0; i < sample_ranges.size(); ++i) {
      if (!iter->ReadInt(&sample_ranges[i]))
        return nullptr;
    }
  
    HistogramBase* histogram = CustomHistogram::FactoryGet(
        histogram_name, sample_ranges, flags);
    if (!ValidateRangeChecksum(*histogram, range_checksum)) {
      // The serialized histogram might be corrupted.
      return nullptr;
    }
    return histogram;
  }
  
  // static
  bool CustomHistogram::ValidateCustomRanges(
      const std::vector<Sample>& custom_ranges) {
    bool has_valid_range = false;
    for (uint32_t i = 0; i < custom_ranges.size(); i++) {
      Sample sample = custom_ranges[i];
      if (sample < 0 || sample > HistogramBase::kSampleType_MAX - 1)
        return false;
      if (sample != 0)
        has_valid_range = true;
    }
    return has_valid_range;
  }
  
  }  // namespace base
  