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 CHROME_COMMON_METRICS_CACHING_PERMUTED_ENTROPY_PROVIDER_H_ 6 #define CHROME_COMMON_METRICS_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 "chrome/common/metrics/proto/permuted_entropy_cache.pb.h" 12 #include "components/variations/entropy_provider.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 virtual ~CachingPermutedEntropyProvider(); 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 virtual 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 // CHROME_COMMON_METRICS_CACHING_PERMUTED_ENTROPY_PROVIDER_H_ 66