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| 1 // Copyright (c) 2010 The Chromium OS 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 METRICS_COUNTER_H_ |
| 6 #define METRICS_COUNTER_H_ |
| 7 |
| 8 #include <gtest/gtest_prod.h> // for FRIEND_TEST |
| 9 |
| 10 namespace chromeos_metrics { |
| 11 |
| 12 // TaggedCounter maintains a persistent storage (i.e., a file) |
| 13 // aggregation counter for a given tag (e.g., day, hour) that survives |
| 14 // system shutdowns, reboots and crashes, as well as daemon process |
| 15 // restarts. The counter object is initialized by pointing to the |
| 16 // persistent storage file and providing a callback used for reporting |
| 17 // aggregated data. The counter can then be updated with additional |
| 18 // event counts. The aggregated count is reported through the |
| 19 // callback when the counter is explicitly flushed or when data for a |
| 20 // new tag arrives. |
| 21 class TaggedCounterInterface { |
| 22 public: |
| 23 // Callback type used for reporting aggregated or flushed data. |
| 24 // Once this callback is invoked by the counter, the reported |
| 25 // aggregated data is discarded. Only aggregated data with positive |
| 26 // counts is reported. |
| 27 // |
| 28 // |handle| is the |reporter_handle| pointer passed through Init. |
| 29 // |tag| is the tag associated with the aggregated count. |
| 30 // |count| is aggregated count. |
| 31 typedef void (*Reporter)(void* handle, int tag, int count); |
| 32 |
| 33 virtual ~TaggedCounterInterface() {} |
| 34 |
| 35 // Initializes the counter by providing the persistent storage |
| 36 // location |filename| and a |reporter| callback for reporting |
| 37 // aggregated counts. |reporter_handle| is sent to the |reporter| |
| 38 // along with the aggregated counts. |
| 39 // |
| 40 // NOTE: The assumption is that this object is the sole owner of the |
| 41 // persistent storage file so no locking is currently implemented. |
| 42 virtual void Init(const char* filename, |
| 43 Reporter reporter, void* reporter_handle) = 0; |
| 44 |
| 45 // Adds |count| of events for the given |tag|. If there's an |
| 46 // existing aggregated count for a different tag, it's reported |
| 47 // through the reporter callback and discarded. |
| 48 virtual void Update(int tag, int count) = 0; |
| 49 |
| 50 // Reports the current aggregated count (if any) through the |
| 51 // reporter callback and discards it. |
| 52 virtual void Flush() = 0; |
| 53 }; |
| 54 |
| 55 class TaggedCounter : public TaggedCounterInterface { |
| 56 public: |
| 57 TaggedCounter(); |
| 58 ~TaggedCounter(); |
| 59 |
| 60 // Implementation of interface methods. |
| 61 void Init(const char* filename, Reporter reporter, void* reporter_handle); |
| 62 void Update(int tag, int count); |
| 63 void Flush(); |
| 64 |
| 65 private: |
| 66 friend class RecordTest; |
| 67 friend class TaggedCounterTest; |
| 68 FRIEND_TEST(TaggedCounterTest, BadFileLocation); |
| 69 FRIEND_TEST(TaggedCounterTest, Flush); |
| 70 FRIEND_TEST(TaggedCounterTest, InitFromFile); |
| 71 FRIEND_TEST(TaggedCounterTest, Update); |
| 72 |
| 73 // The current tag/count record is cached by the counter object to |
| 74 // avoid potentially unnecessary I/O. The cached record can be in |
| 75 // one of the following states: |
| 76 enum RecordState { |
| 77 kRecordInvalid, // Invalid record, sync from persistent storage needed. |
| 78 kRecordNull, // No current record, persistent storage synced. |
| 79 kRecordNullDirty, // No current record, persistent storage is invalid. |
| 80 kRecordValid, // Current record valid, persistent storage synced. |
| 81 kRecordValidDirty // Current record valid, persistent storage is invalid. |
| 82 }; |
| 83 |
| 84 // Defines the tag/count record. Objects of this class are synced |
| 85 // with the persistent storage through binary reads/writes. |
| 86 class Record { |
| 87 public: |
| 88 // Creates a new Record with |tag_| and |count_| reset to 0. |
| 89 Record() : tag_(0), count_(0) {} |
| 90 |
| 91 // Initializes with |tag| and |count|. If |count| is negative, |
| 92 // |count_| is set to 0. |
| 93 void Init(int tag, int count); |
| 94 |
| 95 // Adds |count| to the current |count_|. Negative |count| is |
| 96 // ignored. In case of positive overflow, |count_| is saturated to |
| 97 // INT_MAX. |
| 98 void Add(int count); |
| 99 |
| 100 int tag() const { return tag_; } |
| 101 int count() const { return count_; } |
| 102 |
| 103 private: |
| 104 int tag_; |
| 105 int count_; |
| 106 }; |
| 107 |
| 108 // Implementation of the Update and Flush methods. Goes through the |
| 109 // necessary steps to read, report, update, and sync the aggregated |
| 110 // record. |
| 111 void UpdateInternal(int tag, int count, bool flush); |
| 112 |
| 113 // If the current cached record is invalid, reads it from persistent |
| 114 // storage specified through file descriptor |fd| and updates the |
| 115 // cached record state to either null, or valid depending on the |
| 116 // persistent storage contents. |
| 117 void ReadRecord(int fd); |
| 118 |
| 119 // If there's an existing valid record and either |flush| is true, |
| 120 // or the new |tag| is different than the old one, reports the |
| 121 // aggregated data through the reporter callback and resets the |
| 122 // cached record. |
| 123 void ReportRecord(int tag, bool flush); |
| 124 |
| 125 // Updates the cached record given the new |tag| and |count|. This |
| 126 // method expects either a null cached record, or a valid cached |
| 127 // record with the same tag as |tag|. |
| 128 void UpdateRecord(int tag, int count); |
| 129 |
| 130 // If the cached record state is dirty, updates the persistent |
| 131 // storage specified through file descriptor |fd| and switches the |
| 132 // record state to non-dirty. |
| 133 void WriteRecord(int fd); |
| 134 |
| 135 // Persistent storage file path. |
| 136 const char* filename_; |
| 137 |
| 138 // Aggregated data reporter callback and handle to pass-through. |
| 139 Reporter reporter_; |
| 140 void* reporter_handle_; |
| 141 |
| 142 // Current cached aggregation record. |
| 143 Record record_; |
| 144 |
| 145 // Current cached aggregation record state. |
| 146 RecordState record_state_; |
| 147 }; |
| 148 |
| 149 } // namespace chromeos_metrics |
| 150 |
| 151 #endif // METRICS_COUNTER_H_ |
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