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