Trace tracing Start/Stop events.

webrtc/base/event_tracer.cc

 /*
  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 #include "webrtc/base/event_tracer.h"
@@ skipping 140 matching lines @@
       // log events from a previous logging session (which may be days old).
       trace_events_.clear();
     }
     // Enable event logging (fast-path). This should be disabled since starting
     // shouldn't be done twice.
     RTC_CHECK_EQ(0,
                  rtc::AtomicOps::CompareAndSwap(&g_event_logging_active, 0, 1));
 
     // Finally start, everything should be set up now.
     logging_thread_.Start();
+    TRACE_EVENT_INSTANT0("webrtc", "EventLogger::Start");

[tommi, 2016/02/29 13:12:27]

would TRACE_EVENT_BEGIN0 and TRACE_EVENT_END0 be more appropriate?

Also, Start() and Stop() must occur on the same thread then but I don't see any
thread checks.

[pbos-webrtc, 2016/02/29 13:23:43]

I don't think it's particularly useful to have a begin/end event that spans the
entire tracing period (it'd just add one bar that spans the entire graph). Added
thread checks.

   }
 
   void Stop() {
+    TRACE_EVENT_INSTANT0("webrtc", "EventLogger::Stop");
     // Try to stop. Abort if we're not currently logging.
     if (rtc::AtomicOps::CompareAndSwap(&g_event_logging_active, 1, 0) == 0)
       return;
 
     // Wake up logging thread to finish writing.
     shutdown_event_.Set();
     // Join the logging thread.
     logging_thread_.Stop();
   }
 
@@ skipping 87 matching lines @@
   RTC_DCHECK(old_logger);
   RTC_CHECK(rtc::AtomicOps::CompareAndSwapPtr(
                 &g_event_logger, old_logger,
                 static_cast<EventLogger*>(nullptr)) == old_logger);
   delete old_logger;
   webrtc::SetupEventTracer(nullptr, nullptr);
 }
 
 }  // namespace tracing
 }  // namespace rtc