ash/metrics/task_switch_time_tracker.h

   1 // Copyright 2015 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 ASH_METRICS_TASK_SWITCH_TIME_TRACKER_H_
   6 #define ASH_METRICS_TASK_SWITCH_TIME_TRACKER_H_
   7
   8 #include <string>
   9
  10 #include "ash/ash_export.h"
  11 #include "base/memory/scoped_ptr.h"
  12 #include "base/time/time.h"
  13
  14 namespace base {
  15 class HistogramBase;
  16 class TickClock;
  17 }
  18
  19 namespace ash {
  20
  21 namespace test {
  22 class TaskSwitchTimeTrackerTestAPI;
  23 }  // namespace test
  24
  25 // Tracks time deltas between task switches and records them in a histogram.
  26 class ASH_EXPORT TaskSwitchTimeTracker {
  27  public:
  28   // Create a TaskSwitchTimeTracker that will record data to the histogram with
  29   // the given |histogram_name|.
  30   explicit TaskSwitchTimeTracker(const std::string& histogram_name);
  31
  32   ~TaskSwitchTimeTracker();
  33
  34   // Notifies |this| that a task switch has occurred. A histogram data point
  35   // will be recorded for all calls but the first.
  36   void OnTaskSwitch();
  37
  38  private:
  39   friend class test::TaskSwitchTimeTrackerTestAPI;
  40
  41   // Private constructor that the test::TaskSwitchTimeTrackerTestAPI can use to
  42   // inject a custom |tick_clock|.
  43   TaskSwitchTimeTracker(const std::string& histogram_name,
  44                         scoped_ptr<base::TickClock> tick_clock);
  45
  46   // Returns true if |last_action_time_| has a valid value.
  47   bool HasLastActionTime() const;
  48
  49   // Sets the |last_action_time_| to |tick_clock_|'s current value and returns
  50   // the previous value for |last_action_time_|.
  51   base::TimeTicks SetLastActionTime();
  52
  53   // Records a data point in the histogram.
  54   void RecordTimeDelta();
  55
  56   // Lazily obtains and sets the |histogram_|.
  57   base::HistogramBase* GetHistogram();
  58
  59   // The histogram name to record data to.
  60   std::string histogram_name_;
  61
  62   // The histogram to log data to. Set via GetHistogram() using lazy load.
  63   base::HistogramBase* histogram_ = nullptr;
  64
  65   // Tracks the last time OnTaskSwitch() was called. A value of
  66   // base::TimeTicks() should be interpreted as not set.
  67   base::TimeTicks last_action_time_ = base::TimeTicks();
  68
  69   // The clock used to determine the |last_action_time_|.
  70   scoped_ptr<base::TickClock> tick_clock_;
  71
  72   DISALLOW_COPY_AND_ASSIGN(TaskSwitchTimeTracker);
  73 };
  74
  75 }  // namespace ash
  76
  77 #endif  // ASH_METRICS_TASK_SWITCH_TIME_TRACKE_H_