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

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+// Copyright 2016 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.
+
+// 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 <map>
+#include <memory>
+
+#include "base/compiler_specific.h"
+#include "base/macros.h"
+#include "base/metrics/histogram_base.h"
+#include "base/metrics/histogram_samples.h"
+#include "base/metrics/persistent_memory_allocator.h"
+
+namespace base {
+
+class PersistentHistogramAllocator;
+class PersistentSampleMapRecords;
+
+// 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:
+  // Constructs a persistent sample map using a PersistentHistogramAllocator
+  // as the data source for persistent records.
+  PersistentSampleMap(uint64_t id,
+                      PersistentHistogramAllocator* allocator,
+                      Metadata* meta);
+
+  ~PersistentSampleMap() override;
+
+  // HistogramSamples:
+  void Accumulate(HistogramBase::Sample value,
+                  HistogramBase::Count count) override;
+  HistogramBase::Count GetCount(HistogramBase::Sample value) const override;
+  HistogramBase::Count TotalCount() const override;
+  std::unique_ptr<SampleCountIterator> Iterator() const override;
+
+  // Uses a persistent-memory |iterator| to locate and return information about
+  // the next record holding information for a PersistentSampleMap. 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);
+
+  // 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::Sample value);
+
+ protected:
+  // Performs arithemetic. |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.
+  HistogramBase::Count* GetSampleCountStorage(HistogramBase::Sample value);
+
+  // Gets a pointer to a "count" corresponding to a given |value|, creating
+  // the sample (initialized to zero) if it does not already exists.
+  HistogramBase::Count* GetOrCreateSampleCountStorage(
+      HistogramBase::Sample value);
+
+ private:
+  // Gets the object that manages persistent records. This returns the
+  // |records_| member after first initializing it if necessary.
+  PersistentSampleMapRecords* GetRecords();
+
+  // 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
+  // true for |import_everything| to force the importing of all available
+  // samples even if a match is found.
+  HistogramBase::Count* ImportSamples(HistogramBase::Sample until_value,
+                                      bool import_everything);
+
+  // 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.
+  std::map<HistogramBase::Sample, HistogramBase::Count*> 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.
+  PersistentHistogramAllocator* allocator_;
+
+  // The object that manages sample records inside persistent memory. This is
+  // owned by the |allocator_| object (above) and so, like it, is expected to
+  // live beyond the life of this object. This value is lazily-initialized on
+  // first use via the GetRecords() accessor method.
+  PersistentSampleMapRecords* records_ = nullptr;
+
+  DISALLOW_COPY_AND_ASSIGN(PersistentSampleMap);
+};
+
+}  // namespace base
+
+#endif  // BASE_METRICS_PERSISTENT_SAMPLE_MAP_H_