Allow multiple logging::LogMessage{Handler,Listener}s

base/logging_win.cc

 // Copyright (c) 2011 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.
 
 #include "base/logging_win.h"
 #include "base/memory/singleton.h"
 #include <initguid.h>  // NOLINT
 
 namespace logging {
 
@@ skipping 70 matching lines @@
     event.SetField(2, sizeof(line), &line);
     // The file.
     event.SetField(3, strlen(file) + 1, file);
     // And finally the message.
     event.SetField(4, message.length() + 1 - message_start,
         message.c_str() + message_start);
 
     provider->Log(event.get());
   }
 
-  // Don't increase verbosity in other log destinations.
+  // Don't increase verbosity in other log destinations below this handler

[wychen, 2016/07/09 21:21:20]

The verbosity is still increased for handlers above the current one in the
stack, and all listeners. Is this filtering still useful? If not, we can convert
this to a listener as well.

+  // in the handler stack.
   if (severity < provider->old_log_level_)
     return true;
 
   return false;
 }
 
 void LogEventProvider::Initialize(const GUID& provider_name) {
   LogEventProvider* provider = LogEventProvider::GetInstance();
 
   provider->set_provider_name(provider_name);
   provider->Register();
 
   // Register our message handler with logging.
-  SetLogMessageHandler(LogMessage);
+  PushLogMessageHandler(LogMessage);
 }
 
 void LogEventProvider::Uninitialize() {
   LogEventProvider::GetInstance()->Unregister();
+  PopLogMessageHandler(LogMessage);
 }
 
 void LogEventProvider::OnEventsEnabled() {
   // Grab the old log level so we can restore it later.
   old_log_level_ = GetMinLogLevel();
 
   // Convert the new trace level to a logging severity
   // and enable logging at that level.
   EtwEventLevel level = enable_level();
   if (level == TRACE_LEVEL_NONE || level == TRACE_LEVEL_FATAL) {
     SetMinLogLevel(LOG_FATAL);
   } else if (level == TRACE_LEVEL_ERROR) {
     SetMinLogLevel(LOG_ERROR);
   } else if (level == TRACE_LEVEL_WARNING) {
     SetMinLogLevel(LOG_WARNING);
   } else if (level == TRACE_LEVEL_INFORMATION) {
     SetMinLogLevel(LOG_INFO);
   } else if (level >= TRACE_LEVEL_VERBOSE) {
     // Above INFO, we enable verbose levels with negative severities.
     SetMinLogLevel(TRACE_LEVEL_INFORMATION - level);
   }
 }
 
 void LogEventProvider::OnEventsDisabled() {
   // Restore the old log level.
   SetMinLogLevel(old_log_level_);
 }
 
 }  // namespace logging