components/variations/caching_permuted_entropy_provider.h

   1 // Copyright 2014 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 COMPONENTS_VARIATIONS_CACHING_PERMUTED_ENTROPY_PROVIDER_H_
   6 #define COMPONENTS_VARIATIONS_CACHING_PERMUTED_ENTROPY_PROVIDER_H_
   7
   8 #include "base/basictypes.h"
   9 #include "base/compiler_specific.h"
  10 #include "base/threading/thread_checker.h"
  11 #include "components/variations/entropy_provider.h"
  12 #include "components/variations/proto/permuted_entropy_cache.pb.h"
  13
  14 class PrefService;
  15 class PrefRegistrySimple;
  16
  17 namespace metrics {
  18
  19 // CachingPermutedEntropyProvider is an entropy provider that uses the same
  20 // algorithm as the PermutedEntropyProvider, but caches the results in Local
  21 // State between runs.
  22 class CachingPermutedEntropyProvider : public PermutedEntropyProvider {
  23  public:
  24   // Creates a CachingPermutedEntropyProvider using the given |local_state|
  25   // prefs service with the specified |low_entropy_source|, which should have a
  26   // value in the range of [0, low_entropy_source_max).
  27   CachingPermutedEntropyProvider(PrefService* local_state,
  28                                  uint16 low_entropy_source,
  29                                  size_t low_entropy_source_max);
  30   ~CachingPermutedEntropyProvider() override;
  31
  32   // Registers pref keys used by this class in the Local State pref registry.
  33   static void RegisterPrefs(PrefRegistrySimple* registry);
  34
  35   // Clears the cache in local state. Should be called when the low entropy
  36   // source value gets reset.
  37   static void ClearCache(PrefService* local_state);
  38
  39  private:
  40   // PermutedEntropyProvider overrides:
  41   uint16 GetPermutedValue(uint32 randomization_seed) const override;
  42
  43   // Reads the cache from local state.
  44   void ReadFromLocalState() const;
  45
  46   // Updates local state with the state of the cache.
  47   void UpdateLocalState() const;
  48
  49   // Adds |randomization_seed| -> |value| to the cache.
  50   void AddToCache(uint32 randomization_seed, uint16 value) const;
  51
  52   // Finds the value corresponding to |randomization_seed|, setting |value| and
  53   // returning true if found.
  54   bool FindValue(uint32 randomization_seed, uint16* value) const;
  55
  56   base::ThreadChecker thread_checker_;
  57   PrefService* local_state_;
  58   mutable PermutedEntropyCache cache_;
  59
  60   DISALLOW_COPY_AND_ASSIGN(CachingPermutedEntropyProvider);
  61 };
  62
  63 }  // namespace metrics
  64
  65 #endif  // COMPONENTS_VARIATIONS_CACHING_PERMUTED_ENTROPY_PROVIDER_H_