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// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_METRICS_HISTOGRAM_SNAPSHOT_MANAGER_H_
#define BASE_METRICS_HISTOGRAM_SNAPSHOT_MANAGER_H_
#include <stdint.h>
#include <atomic>
#include <map>
#include <memory>
#include <vector>
#include "base/base_export.h"
#include "base/gtest_prod_util.h"
#include "base/memory/raw_ptr.h"
#include "base/metrics/histogram_base.h"
namespace base {
class HistogramSamples;
class HistogramFlattener;
// HistogramSnapshotManager handles the logistics of gathering up available
// histograms for recording either to disk or for transmission (such as from
// renderer to browser, or from browser to UMA upload). Since histograms can sit
// in memory for an extended period of time, and are vulnerable to memory
// corruption, this class also validates as much redundancy as it can before
// calling for the marginal change (a.k.a., delta) in a histogram to be
// recorded.
class BASE_EXPORT HistogramSnapshotManager final {
public:
explicit HistogramSnapshotManager(HistogramFlattener* histogram_flattener);
HistogramSnapshotManager(const HistogramSnapshotManager&) = delete;
HistogramSnapshotManager& operator=(const HistogramSnapshotManager&) = delete;
~HistogramSnapshotManager();
// Snapshots all histograms and asks |histogram_flattener_| to record the
// delta. |flags_to_set| is used to set flags for each histogram.
// |required_flags| is used to select which histograms to record. Only
// histograms with all of the required flags are selected. If all histograms
// should be recorded, use |Histogram::kNoFlags| as the required flag.
void PrepareDeltas(const std::vector<HistogramBase*>& histograms,
HistogramBase::Flags flags_to_set,
HistogramBase::Flags required_flags);
// When the collection is not so simple as can be done using a single
// iterator, the steps can be performed separately. Call PerpareDelta()
// as many times as necessary. PrepareFinalDelta() works like PrepareDelta()
// except that it does not update the previous logged values and can thus
// be used with read-only files.
void PrepareDelta(HistogramBase* histogram);
void PrepareFinalDelta(const HistogramBase* histogram);
// Used to avoid a dangling pointer `histogram_flattener_` if the referenced
// `HistogramFlattener` is destroyed first.
void ResetFlattener() { histogram_flattener_ = nullptr; }
private:
FRIEND_TEST_ALL_PREFIXES(HistogramSnapshotManagerTest, CheckMerge);
// Capture and hold samples from a histogram. This does all the heavy
// lifting for PrepareDelta() and PrepareFinalDelta().
void PrepareSamples(const HistogramBase* histogram,
const HistogramSamples& samples);
// |histogram_flattener_| handles the logistics of recording the histogram
// deltas.
raw_ptr<HistogramFlattener> histogram_flattener_; // Weak.
};
} // namespace base
#endif // BASE_METRICS_HISTOGRAM_SNAPSHOT_MANAGER_H_
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