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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/macros.h"
17 #include "base/profiler/scoped_profile.h"
18 
19 namespace tracked_objects {
20 
21 // ScopedTracker instruments a region within the code if the instrumentation is
22 // enabled. It can be used, for example, to find out if a source of jankiness is
23 // inside the instrumented code region.
24 // Details:
25 // 1. This class creates a task (like ones created by PostTask calls or IPC
26 // message handlers). This task can be seen in chrome://profiler and is sent as
27 // a part of profiler data to the UMA server. See profiler_event.proto.
28 // 2. That task's lifetime is same as the lifetime of the ScopedTracker
29 // instance.
30 // 3. The execution time associated with the task is the wallclock time between
31 // its constructor and destructor, minus wallclock times of directly nested
32 // tasks.
33 // 4. Task creation that this class utilizes is highly optimized.
34 // 5. The class doesn't create a task unless this was enabled for the current
35 // process. Search for ScopedTracker::Enable for the current list of processes
36 // and channels where it's activated.
37 // 6. The class is designed for temporarily instrumenting code to find
38 // performance problems, after which the instrumentation must be removed.
39 class BASE_EXPORT ScopedTracker {
40  public:
41   ScopedTracker(const Location& location);
42 
43   // Enables instrumentation for the remainder of the current process' life. If
44   // this function is not called, all profiler instrumentations are no-ops.
45   static void Enable();
46 
47   // Augments a |callback| with provided |location|. This is useful for
48   // instrumenting cases when we know that a jank is in a callback and there are
49   // many possible callbacks, but they come from a relatively small number of
50   // places. We can instrument these few places and at least know which one
51   // passes the janky callback.
52   template <typename P1>
TrackCallback(const Location & location,const base::Callback<void (P1)> & callback)53   static base::Callback<void(P1)> TrackCallback(
54       const Location& location,
55       const base::Callback<void(P1)>& callback) {
56     return base::Bind(&ScopedTracker::ExecuteAndTrackCallback<P1>, location,
57                       callback);
58   }
59 
60  private:
61   // Executes |callback|, augmenting it with provided |location|.
62   template <typename P1>
ExecuteAndTrackCallback(const Location & location,const base::Callback<void (P1)> & callback,P1 p1)63   static void ExecuteAndTrackCallback(const Location& location,
64                                       const base::Callback<void(P1)>& callback,
65                                       P1 p1) {
66     ScopedTracker tracking_profile(location);
67     callback.Run(p1);
68   }
69 
70   const ScopedProfile scoped_profile_;
71 
72   DISALLOW_COPY_AND_ASSIGN(ScopedTracker);
73 };
74 
75 }  // namespace tracked_objects
76 
77 #endif  // BASE_PROFILER_SCOPED_TRACKER_H_
78