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

base/logging_win.cc

Index: base/logging_win.cc
diff --git a/base/logging_win.cc b/base/logging_win.cc
index 319ae8a9d38186aa7ffc6466f574c2a795a1832c..421e71cb159379e24872863fedbd7cb1a893f7c9 100644
--- a/base/logging_win.cc
+++ b/base/logging_win.cc
@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #include "base/logging_win.h"
+#include "base/memory/ptr_util.h"
 #include "base/memory/singleton.h"
 #include <initguid.h>  // NOLINT
 
@@ -14,6 +15,9 @@ using base::win::EtwMofEvent;
 DEFINE_GUID(kLogEventId,
     0x7fe69228, 0x633e, 0x4f06, 0x80, 0xc1, 0x52, 0x7f, 0xea, 0x23, 0xe3, 0xa7);
 
+LogEventProvider::WinLogMessageHandler* LogEventProvider::log_handler_ =
+    nullptr;
+
 LogEventProvider::LogEventProvider() : old_log_level_(LOG_NONE) {
 }
 
@@ -22,9 +26,9 @@ LogEventProvider* LogEventProvider::GetInstance() {
                                                LogEventProvider>>::get();
 }
 
-bool LogEventProvider::LogMessage(logging::LogSeverity severity,
-    const char* file, int line, size_t message_start,
-    const std::string& message) {
+bool LogEventProvider::WinLogMessageHandler::OnMessage(
+    logging::LogSeverity severity, const char* file, int line,
+    size_t message_start, const std::string& message) {
   EtwEventLevel level = TRACE_LEVEL_NONE;
 
   // Convert the log severity to the most appropriate ETW trace level.
@@ -88,7 +92,8 @@ bool LogEventProvider::LogMessage(logging::LogSeverity severity,
     provider->Log(event.get());
   }
 
-  // Don't increase verbosity in other log destinations.
+  // Don't increase verbosity in other log destinations below this handler
+  // in the handler stack.
   if (severity < provider->old_log_level_)
     return true;
 
@@ -102,11 +107,13 @@ void LogEventProvider::Initialize(const GUID& provider_name) {
   provider->Register();
 
   // Register our message handler with logging.
-  SetLogMessageHandler(LogMessage);
+  log_handler_ = new WinLogMessageHandler();

[grt (UTC plus 2), 2016/08/05 20:13:30]

can log_handler_ be a non-static member of the provider?

[wychen, 2016/08/12 21:32:39]

Initialize() is a static member, so I think it's natural to put the handler
static as well.

[grt (UTC plus 2), 2016/08/15 07:36:32]

I disagree. Initialize is part of the public API. Presumably, it's static so
that callers can
  LogEventProvider::Initialize(foo);
rather than
  LogEventProvider::GetInstance()->Initialize(foo);

This doesn't mean that implementation details of the provider should also be
statics. old_log_level_, for example, is a data member associated with the
single instance of the LogEventProvider. Making the handler a non-static member
of the provider will also permit you to use std::unique_ptr. It may also make
sense to add a dtor with a DCHECK_EQ(nullptr, log_handler_); to be sure that
Uninitialize was called. If that's important (I'm not sure if it is).

[wychen, 2016/08/17 17:08:54]

Done.

 }
 
 void LogEventProvider::Uninitialize() {
   LogEventProvider::GetInstance()->Unregister();
+  delete log_handler_;
+  log_handler_ = nullptr;
 }
 
 void LogEventProvider::OnEventsEnabled() {