91 lines
3.5 KiB
C++
91 lines
3.5 KiB
C++
// Copyright (c) 2012 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef BASE_METRICS_HISTOGRAM_SNAPSHOT_MANAGER_H_
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#define BASE_METRICS_HISTOGRAM_SNAPSHOT_MANAGER_H_
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#include <stdint.h>
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#include <atomic>
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#include <map>
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#include <string>
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#include <vector>
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#include "base/gtest_prod_util.h"
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#include "base/macros.h"
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#include "base/metrics/histogram_base.h"
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namespace base {
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class HistogramSamples;
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class HistogramFlattener;
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// HistogramSnapshotManager handles the logistics of gathering up available
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// histograms for recording either to disk or for transmission (such as from
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// renderer to browser, or from browser to UMA upload). Since histograms can sit
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// in memory for an extended period of time, and are vulnerable to memory
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// corruption, this class also validates as much redundancy as it can before
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// calling for the marginal change (a.k.a., delta) in a histogram to be
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// recorded.
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class BASE_EXPORT HistogramSnapshotManager final {
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public:
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explicit HistogramSnapshotManager(HistogramFlattener* histogram_flattener);
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~HistogramSnapshotManager();
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// Snapshot all histograms, and ask |histogram_flattener_| to record the
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// delta. |flags_to_set| is used to set flags for each histogram.
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// |required_flags| is used to select histograms to be recorded.
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// Only histograms that have all the flags specified by the argument will be
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// chosen. If all histograms should be recorded, set it to
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// |Histogram::kNoFlags|.
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void PrepareDeltas(const std::vector<HistogramBase*>& histograms,
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HistogramBase::Flags flags_to_set,
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HistogramBase::Flags required_flags);
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// When the collection is not so simple as can be done using a single
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// iterator, the steps can be performed separately. Call PerpareDelta()
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// as many times as necessary. PrepareFinalDelta() works like PrepareDelta()
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// except that it does not update the previous logged values and can thus
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// be used with read-only files.
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void PrepareDelta(HistogramBase* histogram);
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void PrepareFinalDelta(const HistogramBase* histogram);
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private:
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FRIEND_TEST_ALL_PREFIXES(HistogramSnapshotManagerTest, CheckMerge);
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// During a snapshot, samples are acquired and aggregated. This structure
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// contains all the information for a given histogram that persists between
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// collections.
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struct SampleInfo {
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// The set of inconsistencies (flags) already seen for the histogram.
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// See HistogramBase::Inconsistency for values.
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uint32_t inconsistencies = 0;
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};
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// Capture and hold samples from a histogram. This does all the heavy
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// lifting for PrepareDelta() and PrepareAbsolute().
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void PrepareSamples(const HistogramBase* histogram,
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std::unique_ptr<HistogramSamples> samples);
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// |histogram_flattener_| handles the logistics of recording the histogram
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// deltas.
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HistogramFlattener* const histogram_flattener_; // Weak.
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// For histograms, track what has been previously seen, indexed
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// by the hash of the histogram name.
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std::map<uint64_t, SampleInfo> known_histograms_;
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// A flag indicating if a thread is currently doing an operation. This is
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// used to check against concurrent access which is not supported. A Thread-
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// Checker is not sufficient because it may be guarded by at outside lock
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// (as is the case with cronet).
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std::atomic<bool> is_active_;
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DISALLOW_COPY_AND_ASSIGN(HistogramSnapshotManager);
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};
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} // namespace base
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#endif // BASE_METRICS_HISTOGRAM_SNAPSHOT_MANAGER_H_
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