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      1 // Copyright 2016 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 // PersistentSampleMap implements HistogramSamples interface. It is used
      6 // by the SparseHistogram class to store samples in persistent memory which
      7 // allows it to be shared between processes or live across restarts.
      8 
      9 #ifndef BASE_METRICS_PERSISTENT_SAMPLE_MAP_H_
     10 #define BASE_METRICS_PERSISTENT_SAMPLE_MAP_H_
     11 
     12 #include <stdint.h>
     13 
     14 #include <map>
     15 #include <memory>
     16 
     17 #include "base/compiler_specific.h"
     18 #include "base/macros.h"
     19 #include "base/metrics/histogram_base.h"
     20 #include "base/metrics/histogram_samples.h"
     21 #include "base/metrics/persistent_memory_allocator.h"
     22 
     23 namespace base {
     24 
     25 class PersistentHistogramAllocator;
     26 class PersistentSampleMapRecords;
     27 class PersistentSparseHistogramDataManager;
     28 
     29 // The logic here is similar to that of SampleMap but with different data
     30 // structures. Changes here likely need to be duplicated there.
     31 class BASE_EXPORT PersistentSampleMap : public HistogramSamples {
     32  public:
     33   // Constructs a persistent sample map using a PersistentHistogramAllocator
     34   // as the data source for persistent records.
     35   PersistentSampleMap(uint64_t id,
     36                       PersistentHistogramAllocator* allocator,
     37                       Metadata* meta);
     38 
     39   ~PersistentSampleMap() override;
     40 
     41   // HistogramSamples:
     42   void Accumulate(HistogramBase::Sample value,
     43                   HistogramBase::Count count) override;
     44   HistogramBase::Count GetCount(HistogramBase::Sample value) const override;
     45   HistogramBase::Count TotalCount() const override;
     46   std::unique_ptr<SampleCountIterator> Iterator() const override;
     47 
     48   // Uses a persistent-memory |iterator| to locate and return information about
     49   // the next record holding information for a PersistentSampleMap. The record
     50   // could be for any Map so return the |sample_map_id| as well.
     51   static PersistentMemoryAllocator::Reference GetNextPersistentRecord(
     52       PersistentMemoryAllocator::Iterator& iterator,
     53       uint64_t* sample_map_id);
     54 
     55   // Creates a new record in an |allocator| storing count information for a
     56   // specific sample |value| of a histogram with the given |sample_map_id|.
     57   static PersistentMemoryAllocator::Reference CreatePersistentRecord(
     58       PersistentMemoryAllocator* allocator,
     59       uint64_t sample_map_id,
     60       HistogramBase::Sample value);
     61 
     62  protected:
     63   // Performs arithemetic. |op| is ADD or SUBTRACT.
     64   bool AddSubtractImpl(SampleCountIterator* iter, Operator op) override;
     65 
     66   // Gets a pointer to a "count" corresponding to a given |value|. Returns NULL
     67   // if sample does not exist.
     68   HistogramBase::Count* GetSampleCountStorage(HistogramBase::Sample value);
     69 
     70   // Gets a pointer to a "count" corresponding to a given |value|, creating
     71   // the sample (initialized to zero) if it does not already exists.
     72   HistogramBase::Count* GetOrCreateSampleCountStorage(
     73       HistogramBase::Sample value);
     74 
     75  private:
     76   // Gets the object that manages persistent records. This returns the
     77   // |records_| member after first initializing it if necessary.
     78   PersistentSampleMapRecords* GetRecords();
     79 
     80   // Imports samples from persistent memory by iterating over all sample
     81   // records found therein, adding them to the sample_counts_ map. If a
     82   // count for the sample |until_value| is found, stop the import and return
     83   // a pointer to that counter. If that value is not found, null will be
     84   // returned after all currently available samples have been loaded. Pass
     85   // true for |import_everything| to force the importing of all available
     86   // samples even if a match is found.
     87   HistogramBase::Count* ImportSamples(HistogramBase::Sample until_value,
     88                                       bool import_everything);
     89 
     90   // All created/loaded sample values and their associated counts. The storage
     91   // for the actual Count numbers is owned by the |records_| object and its
     92   // underlying allocator.
     93   std::map<HistogramBase::Sample, HistogramBase::Count*> sample_counts_;
     94 
     95   // The allocator that manages histograms inside persistent memory. This is
     96   // owned externally and is expected to live beyond the life of this object.
     97   PersistentHistogramAllocator* allocator_;
     98 
     99   // The object that manages sample records inside persistent memory. This is
    100   // owned by the |allocator_| object (above) and so, like it, is expected to
    101   // live beyond the life of this object. This value is lazily-initialized on
    102   // first use via the GetRecords() accessor method.
    103   PersistentSampleMapRecords* records_ = nullptr;
    104 
    105   DISALLOW_COPY_AND_ASSIGN(PersistentSampleMap);
    106 };
    107 
    108 }  // namespace base
    109 
    110 #endif  // BASE_METRICS_PERSISTENT_SAMPLE_MAP_H_
    111