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// Copyright 2016 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// PersistentSampleMap implements HistogramSamples interface. It is used
// by the SparseHistogram class to store samples in persistent memory which
// allows it to be shared between processes or live across restarts.
#ifndef BASE_METRICS_PERSISTENT_SAMPLE_MAP_H_
#define BASE_METRICS_PERSISTENT_SAMPLE_MAP_H_
#include <stdint.h>
#include <atomic>
#include <map>
#include <memory>
#include <optional>
#include "base/base_export.h"
#include "base/memory/raw_ptr.h"
#include "base/metrics/histogram_base.h"
#include "base/metrics/histogram_samples.h"
#include "base/metrics/persistent_histogram_allocator.h"
#include "base/metrics/persistent_memory_allocator.h"
namespace base {
// The logic here is similar to that of SampleMap but with different data
// structures. Changes here likely need to be duplicated there.
class BASE_EXPORT PersistentSampleMap : public HistogramSamples {
public:
using SampleToCountMap =
std::map<HistogramBase::Sample32,
raw_ptr<std::atomic<HistogramBase::Count32>, CtnExperimental>>;
// Constructs a persistent sample map using a PersistentHistogramAllocator
// as the data source for persistent records.
PersistentSampleMap(uint64_t id,
PersistentHistogramAllocator* allocator,
Metadata* meta);
PersistentSampleMap(const PersistentSampleMap&) = delete;
PersistentSampleMap& operator=(const PersistentSampleMap&) = delete;
~PersistentSampleMap() override;
// HistogramSamples:
void Accumulate(HistogramBase::Sample32 value,
HistogramBase::Count32 count) override;
HistogramBase::Count32 GetCount(HistogramBase::Sample32 value) const override;
HistogramBase::Count32 TotalCount() const override;
std::unique_ptr<SampleCountIterator> Iterator() const override;
std::unique_ptr<SampleCountIterator> ExtractingIterator() override;
bool IsDefinitelyEmpty() const override;
// Uses a persistent-memory |iterator| to locate and return information about
// the next record holding information for a PersistentSampleMap (in
// particular, the reference and the sample |value| it holds). The record
// could be for any Map so return the |sample_map_id| as well.
static PersistentMemoryAllocator::Reference GetNextPersistentRecord(
PersistentMemoryAllocator::Iterator& iterator,
uint64_t* sample_map_id,
HistogramBase::Sample32* value);
// Creates a new record in an |allocator| storing count information for a
// specific sample |value| of a histogram with the given |sample_map_id|.
static PersistentMemoryAllocator::Reference CreatePersistentRecord(
PersistentMemoryAllocator* allocator,
uint64_t sample_map_id,
HistogramBase::Sample32 value);
protected:
// Performs arithmetic. |op| is ADD or SUBTRACT.
bool AddSubtractImpl(SampleCountIterator* iter, Operator op) override;
// Gets a pointer to a "count" corresponding to a given |value|. Returns NULL
// if sample does not exist.
std::atomic<HistogramBase::Count32>* GetSampleCountStorage(
HistogramBase::Sample32 value) const;
// Gets a pointer to a "count" corresponding to a given |value|, creating
// the sample (initialized to zero) if it does not already exist.
std::atomic<HistogramBase::Count32>* GetOrCreateSampleCountStorage(
HistogramBase::Sample32 value);
private:
// Gets the object that manages persistent records. This returns the
// |records_| member after first initializing it if necessary.
PersistentSampleMapRecords* GetRecords() const;
// Imports samples from persistent memory by iterating over all sample records
// found therein, adding them to the sample_counts_ map. If a count for the
// sample |until_value| is found, stop the import and return a pointer to that
// counter. If that value is not found, null will be returned after all
// currently available samples have been loaded. Pass a nullopt for
// |until_value| to force the importing of all available samples (null will
// always be returned in this case).
std::atomic<HistogramBase::Count32>* ImportSamples(
std::optional<HistogramBase::Sample32> until_value = std::nullopt) const;
// All created/loaded sample values and their associated counts. The storage
// for the actual Count numbers is owned by the |records_| object and its
// underlying allocator.
mutable SampleToCountMap sample_counts_;
// The allocator that manages histograms inside persistent memory. This is
// owned externally and is expected to live beyond the life of this object.
mutable raw_ptr<PersistentHistogramAllocator> allocator_;
// The object that manages sample records inside persistent memory. The
// underlying data used is owned by the |allocator_| object (above). This
// value is lazily-initialized on first use via the GetRecords() accessor
// method.
mutable std::unique_ptr<PersistentSampleMapRecords> records_ = nullptr;
};
} // namespace base
#endif // BASE_METRICS_PERSISTENT_SAMPLE_MAP_H_
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