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// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/basictypes.h"
#include "base/compiler_specific.h"
#include "base/threading/thread_checker.h"
#include "components/variations/entropy_provider.h"
#include "components/variations/proto/permuted_entropy_cache.pb.h"
class PrefService;
class PrefRegistrySimple;
namespace metrics {
// CachingPermutedEntropyProvider is an entropy provider that uses the same
// algorithm as the PermutedEntropyProvider, but caches the results in Local
// State between runs.
class CachingPermutedEntropyProvider : public PermutedEntropyProvider {
// Creates a CachingPermutedEntropyProvider using the given |local_state|
// prefs service with the specified |low_entropy_source|, which should have a
// value in the range of [0, low_entropy_source_max).
CachingPermutedEntropyProvider(PrefService* local_state,
uint16 low_entropy_source,
size_t low_entropy_source_max);
virtual ~CachingPermutedEntropyProvider();
// Registers pref keys used by this class in the Local State pref registry.
static void RegisterPrefs(PrefRegistrySimple* registry);
// Clears the cache in local state. Should be called when the low entropy
// source value gets reset.
static void ClearCache(PrefService* local_state);
// PermutedEntropyProvider overrides:
virtual uint16 GetPermutedValue(uint32 randomization_seed) const OVERRIDE;
// Reads the cache from local state.
void ReadFromLocalState() const;
// Updates local state with the state of the cache.
void UpdateLocalState() const;
// Adds |randomization_seed| -> |value| to the cache.
void AddToCache(uint32 randomization_seed, uint16 value) const;
// Finds the value corresponding to |randomization_seed|, setting |value| and
// returning true if found.
bool FindValue(uint32 randomization_seed, uint16* value) const;
base::ThreadChecker thread_checker_;
PrefService* local_state_;
mutable PermutedEntropyCache cache_;
} // namespace metrics