base/profiler/scoped_tracker.h

   1 // Copyright 2014 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_PROFILER_SCOPED_TRACKER_H_
   6 #define BASE_PROFILER_SCOPED_TRACKER_H_
   7
   8 //------------------------------------------------------------------------------
   9 // Utilities for temporarily instrumenting code to dig into issues that were
  10 // found using profiler data.
  11
  12 #include "base/base_export.h"
  13 #include "base/bind.h"
  14 #include "base/callback_forward.h"
  15 #include "base/location.h"
  16 #include "base/profiler/scoped_profile.h"
  17
  18 namespace tracked_objects {
  19
  20 // ScopedTracker instruments a region within the code if the instrumentation is
  21 // enabled. It can be used, for example, to find out if a source of jankiness is
  22 // inside the instrumented code region.
  23 // Details:
  24 // 1. This class creates a task (like ones created by PostTask calls or IPC
  25 // message handlers). This task can be seen in chrome://profiler and is sent as
  26 // a part of profiler data to the UMA server. See profiler_event.proto.
  27 // 2. That task's lifetime is same as the lifetime of the ScopedTracker
  28 // instance.
  29 // 3. The execution time associated with the task is the wallclock time between
  30 // its constructor and destructor, minus wallclock times of directly nested
  31 // tasks.
  32 // 4. Task creation that this class utilizes is highly optimized.
  33 // 5. The class doesn't create a task unless this was enabled for the current
  34 // process. Search for ScopedTracker::Enable for the current list of processes
  35 // and channels where it's activated.
  36 // 6. The class is designed for temporarily instrumenting code to find
  37 // performance problems, after which the instrumentation must be removed.
  38 class BASE_EXPORT ScopedTracker {
  39  public:
  40   ScopedTracker(const Location& location);
  41
  42   // Enables instrumentation for the remainder of the current process' life. If
  43   // this function is not called, all profiler instrumentations are no-ops.
  44   static void Enable();
  45
  46   // Augments a |callback| with provided |location|. This is useful for
  47   // instrumenting cases when we know that a jank is in a callback and there are
  48   // many possible callbacks, but they come from a relatively small number of
  49   // places. We can instrument these few places and at least know which one
  50   // passes the janky callback.
  51   template <typename P1>
  52   static base::Callback<void(P1)> TrackCallback(
  53       const Location& location,
  54       const base::Callback<void(P1)>& callback) {
  55     return base::Bind(&ScopedTracker::ExecuteAndTrackCallback<P1>, location,
  56                       callback);
  57   }
  58
  59  private:
  60   // Executes |callback|, augmenting it with provided |location|.
  61   template <typename P1>
  62   static void ExecuteAndTrackCallback(const Location& location,
  63                                       const base::Callback<void(P1)>& callback,
  64                                       P1 p1) {
  65     ScopedTracker tracking_profile(location);
  66     callback.Run(p1);
  67   }
  68
  69   const ScopedProfile scoped_profile_;
  70
  71   DISALLOW_COPY_AND_ASSIGN(ScopedTracker);
  72 };
  73
  74 }  // namespace tracked_objects
  75
  76 #endif  // BASE_PROFILER_SCOPED_TRACKER_H_