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/observer_list.h"
  21 #include "base/prefs/base_prefs_export.h"
  22 #include "base/prefs/persistent_pref_store.h"
  23 #include "base/threading/non_thread_safe.h"
  24
  25 class PrefFilter;
  26
  27 namespace base {
  28 class Clock;
  29 class DictionaryValue;
  30 class FilePath;
  31 class HistogramBase;
  32 class JsonPrefStoreLossyWriteTest;
  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,
  87                 base::Value* value,
  88                 uint32 flags) override;
  89   void SetValueSilently(const std::string& key,
  90                         base::Value* value,
  91                         uint32 flags) override;
  92   void RemoveValue(const std::string& key, uint32 flags) override;
  93   bool ReadOnly() const override;
  94   PrefReadError GetReadError() const override;
  95   // Note this method may be asynchronous if this instance has a |pref_filter_|
  96   // in which case it will return PREF_READ_ERROR_ASYNCHRONOUS_TASK_INCOMPLETE.
  97   // See details in pref_filter.h.
  98   PrefReadError ReadPrefs() override;
  99   void ReadPrefsAsync(ReadErrorDelegate* error_delegate) override;
 100   void CommitPendingWrite() override;
 101   void ReportValueChanged(const std::string& key, uint32 flags) override;
 102
 103   // Just like RemoveValue(), but doesn't notify observers. Used when doing some
 104   // cleanup that shouldn't otherwise alert observers.
 105   void RemoveValueSilently(const std::string& key, uint32 flags);
 106
 107   // Registers |on_next_successful_write| to be called once, on the next
 108   // successful write event of |writer_|.
 109   void RegisterOnNextSuccessfulWriteCallback(
 110       const base::Closure& on_next_successful_write);
 111
 112  private:
 113   // Represents a histogram for recording the number of writes to the pref file
 114   // that occur every kHistogramWriteReportIntervalInMins minutes.
 115   class BASE_PREFS_EXPORT WriteCountHistogram {
 116    public:
 117     static const int32_t kHistogramWriteReportIntervalMins;
 118
 119     WriteCountHistogram(const base::TimeDelta& commit_interval,
 120                         const base::FilePath& path);
 121     // Constructor for testing. |clock| is a test Clock that is used to retrieve
 122     // the time.
 123     WriteCountHistogram(const base::TimeDelta& commit_interval,
 124                         const base::FilePath& path,
 125                         scoped_ptr<base::Clock> clock);
 126     ~WriteCountHistogram();
 127
 128     // Record that a write has occured.
 129     void RecordWriteOccured();
 130
 131     // Reports writes (that have not yet been reported) in all of the recorded
 132     // intervals that have elapsed up until current time.
 133     void ReportOutstandingWrites();
 134
 135     base::HistogramBase* GetHistogram();
 136
 137    private:
 138     // The minimum interval at which writes can occur.
 139     const base::TimeDelta commit_interval_;
 140
 141     // The path to the file.
 142     const base::FilePath path_;
 143
 144     // Clock which is used to retrieve the current time.
 145     scoped_ptr<base::Clock> clock_;
 146
 147     // The interval at which to report write counts.
 148     const base::TimeDelta report_interval_;
 149
 150     // The time at which the last histogram value was reported for the number
 151     // of write counts.
 152     base::Time last_report_time_;
 153
 154     // The number of writes that have occured since the last write count was
 155     // reported.
 156     uint32_t writes_since_last_report_;
 157
 158     DISALLOW_COPY_AND_ASSIGN(WriteCountHistogram);
 159   };
 160
 161   FRIEND_TEST_ALL_PREFIXES(base::JsonPrefStoreTest,
 162                            WriteCountHistogramTestBasic);
 163   FRIEND_TEST_ALL_PREFIXES(base::JsonPrefStoreTest,
 164                            WriteCountHistogramTestSinglePeriod);
 165   FRIEND_TEST_ALL_PREFIXES(base::JsonPrefStoreTest,
 166                            WriteCountHistogramTestMultiplePeriods);
 167   FRIEND_TEST_ALL_PREFIXES(base::JsonPrefStoreTest,
 168                            WriteCountHistogramTestPeriodWithGaps);
 169   friend class base::JsonPrefStoreLossyWriteTest;
 170
 171   ~JsonPrefStore() override;
 172
 173   // This method is called after the JSON file has been read.  It then hands
 174   // |value| (or an empty dictionary in some read error cases) to the
 175   // |pref_filter| if one is set. It also gives a callback pointing at
 176   // FinalizeFileRead() to that |pref_filter_| which is then responsible for
 177   // invoking it when done. If there is no |pref_filter_|, FinalizeFileRead()
 178   // is invoked directly.
 179   void OnFileRead(scoped_ptr<ReadResult> read_result);
 180
 181   // ImportantFileWriter::DataSerializer overrides:
 182   bool SerializeData(std::string* output) override;
 183
 184   // This method is called after the JSON file has been read and the result has
 185   // potentially been intercepted and modified by |pref_filter_|.
 186   // |initialization_successful| is pre-determined by OnFileRead() and should
 187   // be used when reporting OnInitializationCompleted().
 188   // |schedule_write| indicates whether a write should be immediately scheduled
 189   // (typically because the |pref_filter_| has already altered the |prefs|) --
 190   // this will be ignored if this store is read-only.
 191   void FinalizeFileRead(bool initialization_successful,
 192                         scoped_ptr<base::DictionaryValue> prefs,
 193                         bool schedule_write);
 194
 195   // Schedule a write with the file writer as long as |flags| doesn't contain
 196   // WriteablePrefStore::LOSSY_PREF_WRITE_FLAG.
 197   void ScheduleWrite(uint32 flags);
 198
 199   const base::FilePath path_;
 200   const base::FilePath alternate_path_;
 201   const scoped_refptr<base::SequencedTaskRunner> sequenced_task_runner_;
 202
 203   scoped_ptr<base::DictionaryValue> prefs_;
 204
 205   bool read_only_;
 206
 207   // Helper for safely writing pref data.
 208   base::ImportantFileWriter writer_;
 209
 210   scoped_ptr<PrefFilter> pref_filter_;
 211   ObserverList<PrefStore::Observer, true> observers_;
 212
 213   scoped_ptr<ReadErrorDelegate> error_delegate_;
 214
 215   bool initialized_;
 216   bool filtering_in_progress_;
 217   bool pending_lossy_write_;
 218   PrefReadError read_error_;
 219
 220   std::set<std::string> keys_need_empty_value_;
 221
 222   WriteCountHistogram write_count_histogram_;
 223
 224   DISALLOW_COPY_AND_ASSIGN(JsonPrefStore);
 225 };
 226
 227 #endif  // BASE_PREFS_JSON_PREF_STORE_H_