base/prefs/json_pref_store.h

   1 // Copyright (c) 2012 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 BASE_PREFS_JSON_PREF_STORE_H_
   6 #define BASE_PREFS_JSON_PREF_STORE_H_
   7
   8 #include <set>
   9 #include <string>
  10
  11 #include "base/basictypes.h"
  12 #include "base/callback_forward.h"
  13 #include "base/compiler_specific.h"
  14 #include "base/files/file_path.h"
  15 #include "base/files/important_file_writer.h"
  16 #include "base/gtest_prod_util.h"
  17 #include "base/memory/scoped_ptr.h"
  18 #include "base/memory/scoped_vector.h"
  19 #include "base/memory/weak_ptr.h"
  20 #include "base/message_loop/message_loop_proxy.h"
  21 #include "base/observer_list.h"
  22 #include "base/prefs/base_prefs_export.h"
  23 #include "base/prefs/persistent_pref_store.h"
  24 #include "base/threading/non_thread_safe.h"
  25
  26 class PrefFilter;
  27
  28 namespace base {
  29 class Clock;
  30 class DictionaryValue;
  31 class FilePath;
  32 class HistogramBase;
  33 class SequencedTaskRunner;
  34 class SequencedWorkerPool;
  35 class Value;
  36 FORWARD_DECLARE_TEST(JsonPrefStoreTest, WriteCountHistogramTestBasic);
  37 FORWARD_DECLARE_TEST(JsonPrefStoreTest, WriteCountHistogramTestSinglePeriod);
  38 FORWARD_DECLARE_TEST(JsonPrefStoreTest, WriteCountHistogramTestMultiplePeriods);
  39 FORWARD_DECLARE_TEST(JsonPrefStoreTest, WriteCountHistogramTestPeriodWithGaps);
  40 }
  41
  42 // A writable PrefStore implementation that is used for user preferences.
  43 class BASE_PREFS_EXPORT JsonPrefStore
  44     : public PersistentPrefStore,
  45       public base::ImportantFileWriter::DataSerializer,
  46       public base::SupportsWeakPtr<JsonPrefStore>,
  47       public base::NonThreadSafe {
  48  public:
  49   struct ReadResult;
  50
  51   // Returns instance of SequencedTaskRunner which guarantees that file
  52   // operations on the same file will be executed in sequenced order.
  53   static scoped_refptr<base::SequencedTaskRunner> GetTaskRunnerForFile(
  54       const base::FilePath& pref_filename,
  55       base::SequencedWorkerPool* worker_pool);
  56
  57   // Same as the constructor below with no alternate filename.
  58   JsonPrefStore(
  59       const base::FilePath& pref_filename,
  60       const scoped_refptr<base::SequencedTaskRunner>& sequenced_task_runner,
  61       scoped_ptr<PrefFilter> pref_filter);
  62
  63   // |sequenced_task_runner| must be a shutdown-blocking task runner, ideally
  64   // created by the GetTaskRunnerForFile() method above.
  65   // |pref_filename| is the path to the file to read prefs from.
  66   // |pref_alternate_filename| is the path to an alternate file which the
  67   // desired prefs may have previously been written to. If |pref_filename|
  68   // doesn't exist and |pref_alternate_filename| does, |pref_alternate_filename|
  69   // will be moved to |pref_filename| before the read occurs.
  70   JsonPrefStore(
  71       const base::FilePath& pref_filename,
  72       const base::FilePath& pref_alternate_filename,
  73       const scoped_refptr<base::SequencedTaskRunner>& sequenced_task_runner,
  74       scoped_ptr<PrefFilter> pref_filter);
  75
  76   // PrefStore overrides:
  77   bool GetValue(const std::string& key,
  78                 const base::Value** result) const override;
  79   void AddObserver(PrefStore::Observer* observer) override;
  80   void RemoveObserver(PrefStore::Observer* observer) override;
  81   bool HasObservers() const override;
  82   bool IsInitializationComplete() const override;
  83
  84   // PersistentPrefStore overrides:
  85   bool GetMutableValue(const std::string& key, base::Value** result) override;
  86   void SetValue(const std::string& key, base::Value* value) override;
  87   void SetValueSilently(const std::string& key, base::Value* value) override;
  88   void RemoveValue(const std::string& key) override;
  89   bool ReadOnly() const override;
  90   PrefReadError GetReadError() const override;
  91   // Note this method may be asynchronous if this instance has a |pref_filter_|
  92   // in which case it will return PREF_READ_ERROR_ASYNCHRONOUS_TASK_INCOMPLETE.
  93   // See details in pref_filter.h.
  94   PrefReadError ReadPrefs() override;
  95   void ReadPrefsAsync(ReadErrorDelegate* error_delegate) override;
  96   void CommitPendingWrite() override;
  97   void ReportValueChanged(const std::string& key) override;
  98
  99   // Just like RemoveValue(), but doesn't notify observers. Used when doing some
 100   // cleanup that shouldn't otherwise alert observers.
 101   void RemoveValueSilently(const std::string& key);
 102
 103   // Registers |on_next_successful_write| to be called once, on the next
 104   // successful write event of |writer_|.
 105   void RegisterOnNextSuccessfulWriteCallback(
 106       const base::Closure& on_next_successful_write);
 107
 108  private:
 109   // Represents a histogram for recording the number of writes to the pref file
 110   // that occur every kHistogramWriteReportIntervalInMins minutes.
 111   class BASE_PREFS_EXPORT WriteCountHistogram {
 112    public:
 113     static const int32_t kHistogramWriteReportIntervalMins;
 114
 115     WriteCountHistogram(const base::TimeDelta& commit_interval,
 116                         const base::FilePath& path);
 117     // Constructor for testing. |clock| is a test Clock that is used to retrieve
 118     // the time.
 119     WriteCountHistogram(const base::TimeDelta& commit_interval,
 120                         const base::FilePath& path,
 121                         scoped_ptr<base::Clock> clock);
 122     ~WriteCountHistogram();
 123
 124     // Record that a write has occured.
 125     void RecordWriteOccured();
 126
 127     // Reports writes (that have not yet been reported) in all of the recorded
 128     // intervals that have elapsed up until current time.
 129     void ReportOutstandingWrites();
 130
 131     base::HistogramBase* GetHistogram();
 132
 133    private:
 134     // The minimum interval at which writes can occur.
 135     const base::TimeDelta commit_interval_;
 136
 137     // The path to the file.
 138     const base::FilePath path_;
 139
 140     // Clock which is used to retrieve the current time.
 141     scoped_ptr<base::Clock> clock_;
 142
 143     // The interval at which to report write counts.
 144     const base::TimeDelta report_interval_;
 145
 146     // The time at which the last histogram value was reported for the number
 147     // of write counts.
 148     base::Time last_report_time_;
 149
 150     // The number of writes that have occured since the last write count was
 151     // reported.
 152     uint32_t writes_since_last_report_;
 153
 154     DISALLOW_COPY_AND_ASSIGN(WriteCountHistogram);
 155   };
 156
 157   FRIEND_TEST_ALL_PREFIXES(base::JsonPrefStoreTest,
 158                            WriteCountHistogramTestBasic);
 159   FRIEND_TEST_ALL_PREFIXES(base::JsonPrefStoreTest,
 160                            WriteCountHistogramTestSinglePeriod);
 161   FRIEND_TEST_ALL_PREFIXES(base::JsonPrefStoreTest,
 162                            WriteCountHistogramTestMultiplePeriods);
 163   FRIEND_TEST_ALL_PREFIXES(base::JsonPrefStoreTest,
 164                            WriteCountHistogramTestPeriodWithGaps);
 165
 166   ~JsonPrefStore() override;
 167
 168   // This method is called after the JSON file has been read.  It then hands
 169   // |value| (or an empty dictionary in some read error cases) to the
 170   // |pref_filter| if one is set. It also gives a callback pointing at
 171   // FinalizeFileRead() to that |pref_filter_| which is then responsible for
 172   // invoking it when done. If there is no |pref_filter_|, FinalizeFileRead()
 173   // is invoked directly.
 174   void OnFileRead(scoped_ptr<ReadResult> read_result);
 175
 176   // ImportantFileWriter::DataSerializer overrides:
 177   bool SerializeData(std::string* output) override;
 178
 179   // This method is called after the JSON file has been read and the result has
 180   // potentially been intercepted and modified by |pref_filter_|.
 181   // |initialization_successful| is pre-determined by OnFileRead() and should
 182   // be used when reporting OnInitializationCompleted().
 183   // |schedule_write| indicates whether a write should be immediately scheduled
 184   // (typically because the |pref_filter_| has already altered the |prefs|) --
 185   // this will be ignored if this store is read-only.
 186   void FinalizeFileRead(bool initialization_successful,
 187                         scoped_ptr<base::DictionaryValue> prefs,
 188                         bool schedule_write);
 189
 190   const base::FilePath path_;
 191   const base::FilePath alternate_path_;
 192   const scoped_refptr<base::SequencedTaskRunner> sequenced_task_runner_;
 193
 194   scoped_ptr<base::DictionaryValue> prefs_;
 195
 196   bool read_only_;
 197
 198   // Helper for safely writing pref data.
 199   base::ImportantFileWriter writer_;
 200
 201   scoped_ptr<PrefFilter> pref_filter_;
 202   ObserverList<PrefStore::Observer, true> observers_;
 203
 204   scoped_ptr<ReadErrorDelegate> error_delegate_;
 205
 206   bool initialized_;
 207   bool filtering_in_progress_;
 208   PrefReadError read_error_;
 209
 210   std::set<std::string> keys_need_empty_value_;
 211
 212   WriteCountHistogram write_count_histogram_;
 213
 214   DISALLOW_COPY_AND_ASSIGN(JsonPrefStore);
 215 };
 216
 217 #endif  // BASE_PREFS_JSON_PREF_STORE_H_