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// 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.
#ifndef BASE_METRICS_HISTOGRAM_SAMPLES_H_
#define BASE_METRICS_HISTOGRAM_SAMPLES_H_
#include <stddef.h>
#include <stdint.h>
#include "base/atomicops.h"
#include "base/macros.h"
#include "base/memory/scoped_ptr.h"
#include "base/metrics/histogram_base.h"
namespace base {
class Pickle;
class PickleIterator;
class SampleCountIterator;
// HistogramSamples is a container storing all samples of a histogram. All
// elements must be of a fixed width to ensure 32/64-bit interoperability.
// If this structure changes, bump the version number for kTypeIdHistogram
// in histogram_persistence.cc.
class BASE_EXPORT HistogramSamples {
public:
struct Metadata {
// Initialized when the sample-set is first created with a value provided
// by the caller. It is generally used to identify the sample-set across
// threads and processes, though not necessarily uniquely as it is possible
// to have multiple sample-sets representing subsets of the data.
uint64_t id;
// The sum of all the entries, effectivly the sum(sample * count) for
// all samples. Despite being atomic, no guarantees are made on the
// accuracy of this value; there may be races during histogram
// accumulation and snapshotting that we choose to accept. It should
// be treated as approximate.
// TODO(bcwhite): Change this to std::atomic<int64_t>.
int64_t sum;
// A "redundant" count helps identify memory corruption. It redundantly
// stores the total number of samples accumulated in the histogram. We
// can compare this count to the sum of the counts (TotalCount() function),
// and detect problems. Note, depending on the implementation of different
// histogram types, there might be races during histogram accumulation
// and snapshotting that we choose to accept. In this case, the tallies
// might mismatch even when no memory corruption has happened.
HistogramBase::AtomicCount redundant_count;
Metadata() : id(0), sum(0), redundant_count(0) {}
};
explicit HistogramSamples(uint64_t id);
HistogramSamples(uint64_t id, Metadata* meta);
virtual ~HistogramSamples();
virtual void Accumulate(HistogramBase::Sample value,
HistogramBase::Count count) = 0;
virtual HistogramBase::Count GetCount(HistogramBase::Sample value) const = 0;
virtual HistogramBase::Count TotalCount() const = 0;
virtual void Add(const HistogramSamples& other);
// Add from serialized samples.
virtual bool AddFromPickle(PickleIterator* iter);
virtual void Subtract(const HistogramSamples& other);
virtual scoped_ptr<SampleCountIterator> Iterator() const = 0;
virtual bool Serialize(Pickle* pickle) const;
// Accessor fuctions.
uint64_t id() const { return meta_->id; }
int64_t sum() const { return meta_->sum; }
HistogramBase::Count redundant_count() const {
return subtle::NoBarrier_Load(&meta_->redundant_count);
}
protected:
// Based on |op| type, add or subtract sample counts data from the iterator.
enum Operator { ADD, SUBTRACT };
virtual bool AddSubtractImpl(SampleCountIterator* iter, Operator op) = 0;
void IncreaseSum(int64_t diff);
void IncreaseRedundantCount(HistogramBase::Count diff);
private:
// In order to support histograms shared through an external memory segment,
// meta values may be the local storage or external storage depending on the
// wishes of the derived class.
Metadata local_meta_;
Metadata* meta_;
DISALLOW_COPY_AND_ASSIGN(HistogramSamples);
};
class BASE_EXPORT SampleCountIterator {
public:
virtual ~SampleCountIterator();
virtual bool Done() const = 0;
virtual void Next() = 0;
// Get the sample and count at current position.
// |min| |max| and |count| can be NULL if the value is not of interest.
// Requires: !Done();
virtual void Get(HistogramBase::Sample* min,
HistogramBase::Sample* max,
HistogramBase::Count* count) const = 0;
// Get the index of current histogram bucket.
// For histograms that don't use predefined buckets, it returns false.
// Requires: !Done();
virtual bool GetBucketIndex(size_t* index) const;
};
} // namespace base
#endif // BASE_METRICS_HISTOGRAM_SAMPLES_H_
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