blob: 876b107323c7c18863098a46c1ab363cd41917a5 [file] [log] [blame]
// Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef METRICS_COUNTER_H_
#define METRICS_COUNTER_H_
#include <gtest/gtest_prod.h> // for FRIEND_TEST
namespace chromeos_metrics {
// TaggedCounter maintains a persistent storage (i.e., a file)
// aggregation counter for a given tag (e.g., day, hour) that survives
// system shutdowns, reboots and crashes, as well as daemon process
// restarts. The counter object is initialized by pointing to the
// persistent storage file and providing a callback used for reporting
// aggregated data. The counter can then be updated with additional
// event counts. The aggregated count is reported through the
// callback when the counter is explicitly flushed or when data for a
// new tag arrives.
class TaggedCounterInterface {
public:
// Callback type used for reporting aggregated or flushed data.
// Once this callback is invoked by the counter, the reported
// aggregated data is discarded.
//
// |handle| is the |reporter_handle| pointer passed through Init.
// |tag| is the tag associated with the aggregated count.
// |count| is aggregated count.
typedef void (*Reporter)(void* handle, int tag, int count);
virtual ~TaggedCounterInterface() {}
// Initializes the counter by providing the persistent storage
// location |filename| and a |reporter| callback for reporting
// aggregated counts. |reporter_handle| is sent to the |reporter|
// along with the aggregated counts.
//
// NOTE: The assumption is that this object is the sole owner of the
// persistent storage file so no locking is currently implemented.
virtual void Init(const char* filename,
Reporter reporter, void* reporter_handle) = 0;
// Adds |count| of events for the given |tag|. If there's an
// existing aggregated count for a different tag, it's reported
// through the reporter callback and discarded.
virtual void Update(int tag, int count) = 0;
// Reports the current aggregated count (if any) through the
// reporter callback and discards it.
virtual void Flush() = 0;
};
class TaggedCounter : public TaggedCounterInterface {
public:
TaggedCounter();
~TaggedCounter();
// Implementation of interface methods.
void Init(const char* filename, Reporter reporter, void* reporter_handle);
void Update(int tag, int count);
void Flush();
private:
friend class RecordTest;
friend class TaggedCounterTest;
FRIEND_TEST(TaggedCounterTest, BadFileLocation);
FRIEND_TEST(TaggedCounterTest, Flush);
FRIEND_TEST(TaggedCounterTest, InitFromFile);
FRIEND_TEST(TaggedCounterTest, Update);
// The current tag/count record is cached by the counter object to
// avoid potentially unnecessary I/O. The cached record can be in
// one of the following states:
enum RecordState {
kRecordInvalid, // Invalid record, sync from persistent storage needed.
kRecordNull, // No current record, persistent storage synced.
kRecordNullDirty, // No current record, persistent storage is invalid.
kRecordValid, // Current record valid, persistent storage synced.
kRecordValidDirty // Current record valid, persistent storage is invalid.
};
// Defines the tag/count record. Objects of this class are synced
// with the persistent storage through binary reads/writes.
class Record {
public:
// Creates a new Record with |tag_| and |count_| reset to 0.
Record() : tag_(0), count_(0) {}
// Initializes with |tag| and |count|. If |count| is negative,
// |count_| is set to 0.
void Init(int tag, int count);
// Adds |count| to the current |count_|. Negative |count| is
// ignored. In case of positive overflow, |count_| is saturated to
// INT_MAX.
void Add(int count);
int tag() const { return tag_; }
int count() const { return count_; }
private:
int tag_;
int count_;
};
// Implementation of the Update and Flush methods. Goes through the
// necessary steps to read, report, update, and sync the aggregated
// record.
void UpdateInternal(int tag, int count, bool flush);
// If the current cached record is invalid, reads it from persistent
// storage specified through file descriptor |fd| and updates the
// cached record state to either null, or valid depending on the
// persistent storage contents.
void ReadRecord(int fd);
// If there's an existing valid record and either |flush| is true,
// or the new |tag| is different than the old one, reports the
// aggregated data through the reporter callback and resets the
// cached record.
void ReportRecord(int tag, bool flush);
// Updates the cached record given the new |tag| and |count|. This
// method expects either a null cached record, or a valid cached
// record with the same tag as |tag|. If |flush| is true, the method
// asserts that the cached record is null and returns.
void UpdateRecord(int tag, int count, bool flush);
// If the cached record state is dirty, updates the persistent
// storage specified through file descriptor |fd| and switches the
// record state to non-dirty.
void WriteRecord(int fd);
// Persistent storage file path.
const char* filename_;
// Aggregated data reporter callback and handle to pass-through.
Reporter reporter_;
void* reporter_handle_;
// Current cached aggregation record.
Record record_;
// Current cached aggregation record state.
RecordState record_state_;
};
} // namespace chromeos_metrics
#endif // METRICS_COUNTER_H_