1 // Copyright 2016 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_TRACE_EVENT_TRACE_EVENT_FILTER_H_
6 #define BASE_TRACE_EVENT_TRACE_EVENT_FILTER_H_
7 
8 #include <memory>
9 
10 #include "base/base_export.h"
11 #include "base/macros.h"
12 
13 namespace base {
14 namespace trace_event {
15 
16 class TraceEvent;
17 
18 // TraceEventFilter is like iptables for TRACE_EVENT macros. Filters can be
19 // enabled on a per-category basis, hence a single filter instance can serve
20 // more than a TraceCategory. There are two use cases for filters:
21 // 1. Snooping TRACE_EVENT macros without adding them to the TraceLog. This is
22 //    possible by setting the ENABLED_FOR_FILTERING flag on a category w/o
23 //    ENABLED_FOR_RECORDING (see TraceConfig for user-facing configuration).
24 // 2. Filtering TRACE_EVENT macros before they are added to the TraceLog. This
25 //    requires both the ENABLED_FOR_FILTERING and ENABLED_FOR_RECORDING flags
26 //    on the category.
27 // More importantly, filters must be thread-safe. The FilterTraceEvent and
28 // EndEvent methods can be called concurrently as trace macros are hit on
29 // different threads.
30 class BASE_EXPORT TraceEventFilter {
31  public:
32   TraceEventFilter();
33   virtual ~TraceEventFilter();
34 
35   // If the category is ENABLED_FOR_RECORDING, the event is added iff all the
36   // filters enabled for the category return true. false causes the event to be
37   // discarded.
38   virtual bool FilterTraceEvent(const TraceEvent& trace_event) const = 0;
39 
40   // Notifies the end of a duration event when the RAII macro goes out of scope.
41   virtual void EndEvent(const char* category_name,
42                         const char* event_name) const;
43 
44  private:
45   DISALLOW_COPY_AND_ASSIGN(TraceEventFilter);
46 };
47 
48 }  // namespace trace_event
49 }  // namespace base
50 
51 #endif  // BASE_TRACE_EVENT_TRACE_EVENT_FILTER_H_
52