[OBSOLETE] tracing: split trace event filter logic out of TraceLog

base/trace_event/trace_event_filter.h

Index: base/trace_event/trace_event_filter.h
diff --git a/base/trace_event/trace_event_filter.h b/base/trace_event/trace_event_filter.h
new file mode 100644
index 0000000000000000000000000000000000000000..3dd87f58cd171c576ccf1f6d93158144d44268dc
--- /dev/null
+++ b/base/trace_event/trace_event_filter.h
@@ -0,0 +1,55 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_TRACE_EVENT_TRACE_EVENT_FILTER_H_
+#define BASE_TRACE_EVENT_TRACE_EVENT_FILTER_H_
+
+#include <memory>
+
+#include "base/base_export.h"
+#include "base/macros.h"
+
+namespace base {
+namespace trace_event {
+
+class TraceEvent;
+
+// TraceEventFilter is iptables for TRACE_EVENT macros. Filters can be enabled
+// on a per-category basis. There are two use cases for filters:
+// 1. Snooping TRACE_EVENT macros without adding them to the TraceLog. This is
+//    possible by setting the ENABLED_FOR_FILTERING flag on a category w/o
+//    ENABLED_FOR_RECORDING (see TraceConfig for user-facing configuration).
+// 2. Filtering TRACE_EVENT macros before they are added to the TraceLog. This
+//    requiers both the ENABLED_FOR_FILTERING and ENABLED_FOR_RECORDING flags
+//    on the category.
+// TraceEventFilter instances are undefinitely lived: once created are leaked

[ssid, 2016/11/16 10:19:44]

indefinitely

+// forever, although don't have to be necessarily enabled.

[ssid, 2016/11/16 10:19:44]

A reference to event_filter_registry would be nice, to understand how this class
can be used?

+// More importantly, filters must be thread-safe as the FilterTraceEvent and
+// EndEvent methods can be called concurrently as trace macros are hit on
+// different threads.
+class BASE_EXPORT TraceEventFilter {
+ public:
+  TraceEventFilter() {}
+  virtual ~TraceEventFilter() {}
+
+  // If the category is ENABLED_FOR_RECORDING, the event is added iff all the
+  // filters enabled for the category return true. false causes the event to be
+  // dropped on the floor.
+  virtual bool FilterTraceEvent(const TraceEvent& trace_event) const = 0;
+
+  // Notifies the end of a duration event when the RAII macro goes out of scope.
+  virtual void EndEvent(const char* category_name,

[DmitrySkiba, 2016/11/29 17:55:46]

What is the difference between FilterTraceEvent(TRACE_EVENT_PHASE_END) and
EndEvent() ?

+                        const char* event_name) const {}
+
+  // Unique predicate name for the filter, as used in the TraceConfig.
+  virtual const char* name() const = 0;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(TraceEventFilter);
+};
+
+}  // namespace trace_event
+}  // namespace base
+
+#endif  // BASE_TRACE_EVENT_TRACE_EVENT_FILTER_H_