Tracing pre-filtering

base/trace_event/trace_event.h

Index: base/trace_event/trace_event.h
diff --git a/base/trace_event/trace_event.h b/base/trace_event/trace_event.h
index faaccac8eaf34b40ff91b81e633df44246266a6a..261e925cdea776f198afc148d7e89fc149ff7e81 100644
--- a/base/trace_event/trace_event.h
+++ b/base/trace_event/trace_event.h
@@ -76,7 +76,13 @@
   UNLIKELY(*INTERNAL_TRACE_EVENT_UID(category_group_enabled) &           \
            (base::trace_event::TraceLog::ENABLED_FOR_RECORDING |         \
             base::trace_event::TraceLog::ENABLED_FOR_EVENT_CALLBACK |    \
-            base::trace_event::TraceLog::ENABLED_FOR_ETW_EXPORT))
+            base::trace_event::TraceLog::ENABLED_FOR_ETW_EXPORT |        \
+            base::trace_event::TraceLog::ENABLED_FOR_FILTERING))

[Primiano Tucci (use gerrit), 2016/05/31 15:41:23]

Do you really need this or-ed here?
I'd assume that in the case of filtering the category is enabled for (RECORDING
| FILTERING).
Otherwise if the category gets only the ENABLED_FOR_FILTERING flag, you won't be
able to filter the events coming from the subprojects (blink, skia) without
making changes to them.

In other words the question here should be: what is the semantic of saying that
category "foo" is both part of the enabled categories and the filter?
1) It gets always inserted in the trace and is also passed to the filter
2) It is inserted in the trace only if it passes the filter.

[oystein (OOO til 10th of July), 2016/08/01 13:39:49]

I think that's right, 2) makes sense to me. The only reason to keep these
separate would be if the config could essentially override the result of the
filters, or something similar, but that just introduces confused semantics.
Done.

+
+#define INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_FILTERING_MODE( \
+    category_group_enabled)                                             \
+  UNLIKELY(category_group_enabled&                                      \
+               base::trace_event::TraceLog::ENABLED_FOR_FILTERING)
 
 ////////////////////////////////////////////////////////////////////////////////
 // Implementation specific tracing API definitions.
@@ -185,6 +191,14 @@
 #define TRACE_EVENT_API_UPDATE_TRACE_EVENT_DURATION \
     base::trace_event::TraceLog::GetInstance()->UpdateTraceEventDuration
 
+// Call EndEvent on the filter for a filtered event.
+// void TRACE_EVENT_API_UPDATE_TRACE_EVENT_DURATION(
+//     const unsigned char* category_group_enabled,
+//     const char* name,
+//     base::trace_event::TraceEventHandle id)
+#define TRACE_EVENT_API_END_FILTERED_EVENT \
+  base::trace_event::TraceLog::GetInstance()->EndFilteredEvent

[Primiano Tucci (use gerrit), 2016/05/27 17:47:06]

Not sure you need this macro since you need this only in one place

+
 // Adds a metadata event to the trace log. The |AppendValueAsTraceFormat| method
 // on the convertable value will be called at flush time.
 // TRACE_EVENT_API_ADD_METADATA_EVENT(
@@ -974,9 +988,15 @@ class TRACE_EVENT_API_CLASS_EXPORT ScopedTracer {
   ScopedTracer() : p_data_(NULL) {}
 
   ~ScopedTracer() {
-    if (p_data_ && *data_.category_group_enabled)
+    if (p_data_ && *data_.category_group_enabled) {
       TRACE_EVENT_API_UPDATE_TRACE_EVENT_DURATION(
           data_.category_group_enabled, data_.name, data_.event_handle);
+      if (INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_FILTERING_MODE(
+              *data_.category_group_enabled)) {
+        TRACE_EVENT_API_END_FILTERED_EVENT(data_.category_group_enabled,
+                                           data_.name, data_.event_handle);
+      }
+    }
   }
 
   void Initialize(const unsigned char* category_group_enabled,