// 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).
// It supports calls to accumulate either time intervals (which are processed
// as integral number of milliseconds), or arbitrary integral units.
// For Histogram(exponential histogram), LinearHistogram and CustomHistogram,
// the minimum for a declared range is 1 (instead of 0), while the maximum is
// (HistogramBase::kSampleType_MAX - 1). Currently you can declare histograms
// with ranges exceeding those limits (e.g. 0 as minimal or
// HistogramBase::kSampleType_MAX as maximal), but those excesses will be
// silently clamped to those limits (for backwards compatibility with existing
// code). Best practice is to not exceed the limits.
// Each use of a histogram with the same name will reference the same underlying
// data, so it is safe to record to the same histogram from multiple locations
// in the code. It is a runtime error if all uses of the same histogram do not
// agree exactly in type, bucket size and range.
// For Histogram and LinearHistogram, the maximum for a declared range should
// always be larger (not equal) than minimal range. Zero and
// HistogramBase::kSampleType_MAX are implicitly added as first and last ranges,
// so the smallest legal bucket_count is 3. However CustomHistogram can have
// bucket count as 2 (when you give a custom ranges vector containing only 1
// range).
// For these 3 kinds of histograms, the max bucket count is always
// (Histogram::kBucketCount_MAX - 1).
// The buckets layout of class Histogram is exponential. For example, buckets
// might contain (sequentially) the count of values in the following intervals:
// [0,1), [1,2), [2,4), [4,8), [8,16), [16,32), [32,64), [64,infinity)
// That bucket allocation would actually result from construction of a histogram
// for values between 1 and 64, with 8 buckets, such as:
// Histogram count("some name", 1, 64, 8);
// Note that the underflow bucket [0,1) and the overflow bucket [64,infinity)
// are also counted by the constructor in the user supplied "bucket_count"
// argument.
// The above example has an exponential ratio of 2 (doubling the bucket width
// in each consecutive bucket. The Histogram class automatically calculates
// the smallest ratio that it can use to construct the number of buckets
// selected in the constructor. An another example, if you had 50 buckets,
// and millisecond time values from 1 to 10000, then the ratio between
// consecutive bucket widths will be approximately somewhere around the 50th
// root of 10000. This approach provides very fine grain (narrow) buckets
// at the low end of the histogram scale, but allows the histogram to cover a
// gigantic range with the addition of very few buckets.
// Usually we use macros to define and use a histogram, which are defined in
// base/metrics/histogram_macros.h. Note: Callers should include that header
// directly if they only access the histogram APIs through macros.
//
// Macros use a pattern involving a function static variable, that is a pointer
// to a histogram. This static is explicitly initialized on any thread
// that detects a uninitialized (NULL) pointer. The potentially racy
// initialization is not a problem as it is always set to point to the same
// value (i.e., the FactoryGet always returns the same value). FactoryGet
// is also completely thread safe, which results in a completely thread safe,
// and relatively fast, set of counters. To avoid races at shutdown, the static
// pointer is NOT deleted, and we leak the histograms at process termination.
#ifndef BASE_METRICS_HISTOGRAM_H_
#define BASE_METRICS_HISTOGRAM_H_
#include <stddef.h>
#include <stdint.h>
#include <map>
#include <string>
#include <vector>
#include "base/base_export.h"
#include "base/compiler_specific.h"
#include "base/gtest_prod_util.h"
#include "base/logging.h"
#include "base/macros.h"
#include "base/memory/scoped_ptr.h"
#include "base/metrics/bucket_ranges.h"
#include "base/metrics/histogram_base.h"
// TODO(asvitkine): Migrate callers to to include this directly and remove this.
#include "base/metrics/histogram_macros.h"
#include "base/metrics/histogram_samples.h"
#include "base/time/time.h"
namespace base {
class BooleanHistogram;
class CustomHistogram;
class Histogram;
class LinearHistogram;
class Pickle;
class PickleIterator;
class SampleVector;
class BASE_EXPORT Histogram : public HistogramBase {
public:
// Initialize maximum number of buckets in histograms as 16,384.
static const size_t kBucketCount_MAX;
typedef std::vector<Count> Counts;
//----------------------------------------------------------------------------
// For a valid histogram, input should follow these restrictions:
// minimum > 0 (if a minimum below 1 is specified, it will implicitly be
// normalized up to 1)
// maximum > minimum
// buckets > 2 [minimum buckets needed: underflow, overflow and the range]
// Additionally,
// buckets <= (maximum - minimum + 2) - this is to ensure that we don't have
// more buckets than the range of numbers; having more buckets than 1 per
// value in the range would be nonsensical.
static HistogramBase* FactoryGet(const std::string& name,
Sample minimum,
Sample maximum,
size_t bucket_count,
int32_t flags);
static HistogramBase* FactoryTimeGet(const std::string& name,
base::TimeDelta minimum,
base::TimeDelta maximum,
size_t bucket_count,
int32_t flags);
// Overloads of the above two functions that take a const char* |name| param,
// to avoid code bloat from the std::string constructor being inlined into
// call sites.
static HistogramBase* FactoryGet(const char* name,
Sample minimum,
Sample maximum,
size_t bucket_count,
int32_t flags);
static HistogramBase* FactoryTimeGet(const char* name,
base::TimeDelta minimum,
base::TimeDelta maximum,
size_t bucket_count,
int32_t flags);
static void InitializeBucketRanges(Sample minimum,
Sample maximum,
BucketRanges* ranges);
// This constant if for FindCorruption. Since snapshots of histograms are
// taken asynchronously relative to sampling, and our counting code currently
// does not prevent race conditions, it is pretty likely that we'll catch a
// redundant count that doesn't match the sample count. We allow for a
// certain amount of slop before flagging this as an inconsistency. Even with
// an inconsistency, we'll snapshot it again (for UMA in about a half hour),
// so we'll eventually get the data, if it was not the result of a corruption.
static const int kCommonRaceBasedCountMismatch;
// Check to see if bucket ranges, counts and tallies in the snapshot are
// consistent with the bucket ranges and checksums in our histogram. This can
// produce a false-alarm if a race occurred in the reading of the data during
// a SnapShot process, but should otherwise be false at all times (unless we
// have memory over-writes, or DRAM failures).
int FindCorruption(const HistogramSamples& samples) const override;
//----------------------------------------------------------------------------
// Accessors for factory construction, serialization and testing.
//----------------------------------------------------------------------------
Sample declared_min() const { return declared_min_; }
Sample declared_max() const { return declared_max_; }
virtual Sample ranges(size_t i) const;
virtual size_t bucket_count() const;
const BucketRanges* bucket_ranges() const { return bucket_ranges_; }
// This function validates histogram construction arguments. It returns false
// if some of the arguments are totally bad.
// Note. Currently it allow some bad input, e.g. 0 as minimum, but silently
// converts it to good input: 1.
// TODO(kaiwang): Be more restrict and return false for any bad input, and
// make this a readonly validating function.
static bool InspectConstructionArguments(const std::string& name,
Sample* minimum,
Sample* maximum,
size_t* bucket_count);
// HistogramBase implementation:
uint64_t name_hash() const override;
HistogramType GetHistogramType() const override;
bool HasConstructionArguments(Sample expected_minimum,
Sample expected_maximum,
size_t expected_bucket_count) const override;
void Add(Sample value) override;
void AddCount(Sample value, int count) override;
scoped_ptr<HistogramSamples> SnapshotSamples() const override;
void AddSamples(const HistogramSamples& samples) override;
bool AddSamplesFromPickle(base::PickleIterator* iter) override;
void WriteHTMLGraph(std::string* output) const override;
void WriteAscii(std::string* output) const override;
protected:
// |ranges| should contain the underflow and overflow buckets. See top
// comments for example.
Histogram(const std::string& name,
Sample minimum,
Sample maximum,
const BucketRanges* ranges);
~Histogram() override;
// HistogramBase implementation:
bool SerializeInfoImpl(base::Pickle* pickle) const override;
// Method to override to skip the display of the i'th bucket if it's empty.
virtual bool PrintEmptyBucket(size_t index) const;
// Get normalized size, relative to the ranges(i).
virtual double GetBucketSize(Count current, size_t i) const;
// Return a string description of what goes in a given bucket.
// Most commonly this is the numeric value, but in derived classes it may
// be a name (or string description) given to the bucket.
virtual const std::string GetAsciiBucketRange(size_t it) const;
private:
// Allow tests to corrupt our innards for testing purposes.
FRIEND_TEST_ALL_PREFIXES(HistogramTest, BoundsTest);
FRIEND_TEST_ALL_PREFIXES(HistogramTest, BucketPlacementTest);
FRIEND_TEST_ALL_PREFIXES(HistogramTest, CorruptBucketBounds);
FRIEND_TEST_ALL_PREFIXES(HistogramTest, CorruptSampleCounts);
FRIEND_TEST_ALL_PREFIXES(HistogramTest, NameMatchTest);
FRIEND_TEST_ALL_PREFIXES(HistogramTest, AddCountTest);
friend class StatisticsRecorder; // To allow it to delete duplicates.
friend class StatisticsRecorderTest;
friend BASE_EXPORT HistogramBase* DeserializeHistogramInfo(
base::PickleIterator* iter);
static HistogramBase* DeserializeInfoImpl(base::PickleIterator* iter);
// Implementation of SnapshotSamples function.
scoped_ptr<SampleVector> SnapshotSampleVector() const;
//----------------------------------------------------------------------------
// Helpers for emitting Ascii graphic. Each method appends data to output.
void WriteAsciiImpl(bool graph_it,
const std::string& newline,
std::string* output) const;
// Find out how large (graphically) the largest bucket will appear to be.
double GetPeakBucketSize(const SampleVector& samples) const;
// Write a common header message describing this histogram.
void WriteAsciiHeader(const SampleVector& samples,
Count sample_count,
std::string* output) const;
// Write information about previous, current, and next buckets.
// Information such as cumulative percentage, etc.
void WriteAsciiBucketContext(const int64_t past,
const Count current,
const int64_t remaining,
const size_t i,
std::string* output) const;
// WriteJSON calls these.
void GetParameters(DictionaryValue* params) const override;
void GetCountAndBucketData(Count* count,
int64_t* sum,
ListValue* buckets) const override;
// Does not own this object. Should get from StatisticsRecorder.
const BucketRanges* bucket_ranges_;
Sample declared_min_; // Less than this goes into the first bucket.
Sample declared_max_; // Over this goes into the last bucket.
// Finally, provide the state that changes with the addition of each new
// sample.
scoped_ptr<SampleVector> samples_;
DISALLOW_COPY_AND_ASSIGN(Histogram);
};
//------------------------------------------------------------------------------
// LinearHistogram is a more traditional histogram, with evenly spaced
// buckets.
class BASE_EXPORT LinearHistogram : public Histogram {
public:
~LinearHistogram() override;
/* minimum should start from 1. 0 is as minimum is invalid. 0 is an implicit
default underflow bucket. */
static HistogramBase* FactoryGet(const std::string& name,
Sample minimum,
Sample maximum,
size_t bucket_count,
int32_t flags);
static HistogramBase* FactoryTimeGet(const std::string& name,
TimeDelta minimum,
TimeDelta maximum,
size_t bucket_count,
int32_t flags);
// Overloads of the above two functions that take a const char* |name| param,
// to avoid code bloat from the std::string constructor being inlined into
// call sites.
static HistogramBase* FactoryGet(const char* name,
Sample minimum,
Sample maximum,
size_t bucket_count,
int32_t flags);
static HistogramBase* FactoryTimeGet(const char* name,
TimeDelta minimum,
TimeDelta maximum,
size_t bucket_count,
int32_t flags);
struct DescriptionPair {
Sample sample;
const char* description; // Null means end of a list of pairs.
};
// Create a LinearHistogram and store a list of number/text values for use in
// writing the histogram graph.
// |descriptions| can be NULL, which means no special descriptions to set. If
// it's not NULL, the last element in the array must has a NULL in its
// "description" field.
static HistogramBase* FactoryGetWithRangeDescription(
const std::string& name,
Sample minimum,
Sample maximum,
size_t bucket_count,
int32_t flags,
const DescriptionPair descriptions[]);
static void InitializeBucketRanges(Sample minimum,
Sample maximum,
BucketRanges* ranges);
// Overridden from Histogram:
HistogramType GetHistogramType() const override;
protected:
LinearHistogram(const std::string& name,
Sample minimum,
Sample maximum,
const BucketRanges* ranges);
double GetBucketSize(Count current, size_t i) const override;
// If we have a description for a bucket, then return that. Otherwise
// let parent class provide a (numeric) description.
const std::string GetAsciiBucketRange(size_t i) const override;
// Skip printing of name for numeric range if we have a name (and if this is
// an empty bucket).
bool PrintEmptyBucket(size_t index) const override;
private:
friend BASE_EXPORT HistogramBase* DeserializeHistogramInfo(
base::PickleIterator* iter);
static HistogramBase* DeserializeInfoImpl(base::PickleIterator* iter);
// For some ranges, we store a printable description of a bucket range.
// If there is no description, then GetAsciiBucketRange() uses parent class
// to provide a description.
typedef std::map<Sample, std::string> BucketDescriptionMap;
BucketDescriptionMap bucket_description_;
DISALLOW_COPY_AND_ASSIGN(LinearHistogram);
};
//------------------------------------------------------------------------------
// BooleanHistogram is a histogram for booleans.
class BASE_EXPORT BooleanHistogram : public LinearHistogram {
public:
static HistogramBase* FactoryGet(const std::string& name, int32_t flags);
// Overload of the above function that takes a const char* |name| param,
// to avoid code bloat from the std::string constructor being inlined into
// call sites.
static HistogramBase* FactoryGet(const char* name, int32_t flags);
HistogramType GetHistogramType() const override;
private:
BooleanHistogram(const std::string& name, const BucketRanges* ranges);
friend BASE_EXPORT HistogramBase* DeserializeHistogramInfo(
base::PickleIterator* iter);
static HistogramBase* DeserializeInfoImpl(base::PickleIterator* iter);
DISALLOW_COPY_AND_ASSIGN(BooleanHistogram);
};
//------------------------------------------------------------------------------
// CustomHistogram is a histogram for a set of custom integers.
class BASE_EXPORT CustomHistogram : public Histogram {
public:
// |custom_ranges| contains a vector of limits on ranges. Each limit should be
// > 0 and < kSampleType_MAX. (Currently 0 is still accepted for backward
// compatibility). The limits can be unordered or contain duplication, but
// client should not depend on this.
static HistogramBase* FactoryGet(const std::string& name,
const std::vector<Sample>& custom_ranges,
int32_t flags);
// Overload of the above function that takes a const char* |name| param,
// to avoid code bloat from the std::string constructor being inlined into
// call sites.
static HistogramBase* FactoryGet(const char* name,
const std::vector<Sample>& custom_ranges,
int32_t flags);
// Overridden from Histogram:
HistogramType GetHistogramType() const override;
// Helper method for transforming an array of valid enumeration values
// to the std::vector<int> expected by UMA_HISTOGRAM_CUSTOM_ENUMERATION.
// This function ensures that a guard bucket exists right after any
// valid sample value (unless the next higher sample is also a valid value),
// so that invalid samples never fall into the same bucket as valid samples.
// TODO(kaiwang): Change name to ArrayToCustomEnumRanges.
static std::vector<Sample> ArrayToCustomRanges(const Sample* values,
size_t num_values);
protected:
CustomHistogram(const std::string& name,
const BucketRanges* ranges);
// HistogramBase implementation:
bool SerializeInfoImpl(base::Pickle* pickle) const override;
double GetBucketSize(Count current, size_t i) const override;
private:
friend BASE_EXPORT HistogramBase* DeserializeHistogramInfo(
base::PickleIterator* iter);
static HistogramBase* DeserializeInfoImpl(base::PickleIterator* iter);
static bool ValidateCustomRanges(const std::vector<Sample>& custom_ranges);
static BucketRanges* CreateBucketRangesFromCustomRanges(
const std::vector<Sample>& custom_ranges);
DISALLOW_COPY_AND_ASSIGN(CustomHistogram);
};
} // namespace base
#endif // BASE_METRICS_HISTOGRAM_H_