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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_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);
- private:
- FRIEND_TEST_ALL_PREFIXES(HistogramSnapshotManagerTest, CheckMerge);
- // During a snapshot, samples are acquired and aggregated. This structure
- // contains all the information for a given histogram that persists between
- // collections.
- struct SampleInfo {
- // The set of inconsistencies (flags) already seen for the histogram.
- // See HistogramBase::Inconsistency for values.
- uint32_t inconsistencies = 0;
- };
- // Capture and hold samples from a histogram. This does all the heavy
- // lifting for PrepareDelta() and PrepareAbsolute().
- void PrepareSamples(const HistogramBase* histogram,
- std::unique_ptr<HistogramSamples> samples);
- // |histogram_flattener_| handles the logistics of recording the histogram
- // deltas.
- const raw_ptr<HistogramFlattener> histogram_flattener_; // Weak.
- // For histograms, track what has been previously seen, indexed
- // by the hash of the histogram name.
- std::map<uint64_t, SampleInfo> known_histograms_;
- // A flag indicating if a thread is currently doing an operation. This is
- // used to check against concurrent access which is not supported. A Thread-
- // Checker is not sufficient because it may be guarded by at outside lock
- // (as is the case with cronet).
- std::atomic<bool> is_active_;
- };
- } // namespace base
- #endif // BASE_METRICS_HISTOGRAM_SNAPSHOT_MANAGER_H_
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