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