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      1 // Copyright 2013 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #ifndef BASE_METRICS_HISTOGRAM_DELTA_SERIALIZATION_H_
      6 #define BASE_METRICS_HISTOGRAM_DELTA_SERIALIZATION_H_
      7 
      8 #include <memory>
      9 #include <string>
     10 #include <vector>
     11 
     12 #include "base/base_export.h"
     13 #include "base/macros.h"
     14 #include "base/metrics/histogram_flattener.h"
     15 #include "base/metrics/histogram_snapshot_manager.h"
     16 #include "base/threading/thread_checker.h"
     17 
     18 namespace base {
     19 
     20 class HistogramBase;
     21 
     22 // Serializes and restores histograms deltas.
     23 class BASE_EXPORT HistogramDeltaSerialization : public HistogramFlattener {
     24  public:
     25   // |caller_name| is string used in histograms for counting inconsistencies.
     26   explicit HistogramDeltaSerialization(const std::string& caller_name);
     27   ~HistogramDeltaSerialization() override;
     28 
     29   // Computes deltas in histogram bucket counts relative to the previous call to
     30   // this method. Stores the deltas in serialized form into |serialized_deltas|.
     31   // If |serialized_deltas| is null, no data is serialized, though the next call
     32   // will compute the deltas relative to this one. Setting |include_persistent|
     33   // will include histograms held in persistent memory (and thus may be reported
     34   // elsewhere); otherwise only histograms local to this process are serialized.
     35   void PrepareAndSerializeDeltas(std::vector<std::string>* serialized_deltas,
     36                                  bool include_persistent);
     37 
     38   // Deserialize deltas and add samples to corresponding histograms, creating
     39   // them if necessary. Silently ignores errors in |serialized_deltas|.
     40   static void DeserializeAndAddSamples(
     41       const std::vector<std::string>& serialized_deltas);
     42 
     43  private:
     44   // HistogramFlattener implementation.
     45   void RecordDelta(const HistogramBase& histogram,
     46                    const HistogramSamples& snapshot) override;
     47 
     48   ThreadChecker thread_checker_;
     49 
     50   // Calculates deltas in histogram counters.
     51   HistogramSnapshotManager histogram_snapshot_manager_;
     52 
     53   // Output buffer for serialized deltas.
     54   std::vector<std::string>* serialized_deltas_;
     55 
     56   DISALLOW_COPY_AND_ASSIGN(HistogramDeltaSerialization);
     57 };
     58 
     59 }  // namespace base
     60 
     61 #endif  // BASE_METRICS_HISTOGRAM_DELTA_SERIALIZATION_H_
     62