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
14class PrefService;
15class PrefRegistrySimple;
16
17namespace 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.
22class 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  // COMPONENTS_VARIATIONS_CACHING_PERMUTED_ENTROPY_PROVIDER_H_
66