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TMessagesProj/jni/voip/webrtc/base/metrics/histogram_snapshot_manager.h

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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 <string>
+#include <vector>
+
+#include "base/gtest_prod_util.h"
+#include "base/macros.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();
+
+  // Snapshot all histograms, and ask |histogram_flattener_| to record the
+  // delta. |flags_to_set| is used to set flags for each histogram.
+  // |required_flags| is used to select histograms to be recorded.
+  // Only histograms that have all the flags specified by the argument will be
+  // chosen. If all histograms should be recorded, set it to
+  // |Histogram::kNoFlags|.
+  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.
+  HistogramFlattener* const 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_;
+
+  DISALLOW_COPY_AND_ASSIGN(HistogramSnapshotManager);
+};
+
+}  // namespace base
+
+#endif  // BASE_METRICS_HISTOGRAM_SNAPSHOT_MANAGER_H_