Replace ScopedThreadProxy with MessageLoopProxy & WeakPtrs.

remoting/client/plugin/chromoting_instance.cc

Index: remoting/client/plugin/chromoting_instance.cc
diff --git a/remoting/client/plugin/chromoting_instance.cc b/remoting/client/plugin/chromoting_instance.cc
index fec261e1798b874631f86002ad74df10a2ab56fc..75953c3372557fb77d206917cbb0f9f760f02104 100644
--- a/remoting/client/plugin/chromoting_instance.cc
+++ b/remoting/client/plugin/chromoting_instance.cc
@@ -97,7 +97,8 @@ std::string ConnectionErrorToString(ChromotingInstance::ConnectionError error) {
 // while sending the log message to the UI.
 static bool g_logging_to_plugin = false;
 static bool g_has_logging_instance = false;
-static ChromotingInstance* g_logging_instance = NULL;
+static scoped_refptr<base::MessageLoopProxy> g_logging_message_loop;

[Sergey Ulanov, 2012/05/29 18:58:30]

This adds a static finalizer. Use CR_DEFINE_STATIC_LOCAL() here.

[Sergey Ulanov, 2012/05/29 18:58:30]

SingleThreadTaskRunner please.

[Wez, 2012/05/30 00:18:39]

Done.

[Wez, 2012/05/30 00:18:39]

Done.

+static base::WeakPtr<ChromotingInstance> g_logging_instance;

[Sergey Ulanov, 2012/05/29 18:58:30]

This adds a static finalizer. Use CR_DEFINE_STATIC_LOCAL() to avoid it.

[Wez, 2012/05/30 00:18:39]

Done.

 static logging::LogMessageHandlerFunction g_logging_old_handler = NULL;
 
 static base::LazyInstance<base::Lock>::Leaky
@@ -139,7 +140,7 @@ ChromotingInstance::ChromotingInstance(PP_Instance pp_instance)
       plugin_message_loop_(
           new PluginMessageLoopProxy(&plugin_thread_delegate_)),
       context_(plugin_message_loop_),
-      thread_proxy_(new ScopedThreadProxy(plugin_message_loop_)) {
+      weak_factory_(ALLOW_THIS_IN_INITIALIZER_LIST(this)) {
   RequestInputEvents(PP_INPUTEVENT_CLASS_MOUSE | PP_INPUTEVENT_CLASS_WHEEL);
   RequestFilteringInputEvents(PP_INPUTEVENT_CLASS_KEYBOARD);
 
@@ -159,7 +160,7 @@ ChromotingInstance::~ChromotingInstance() {
 
   // Detach the log proxy so we don't log anything else to the UI.
   // This needs to be done before the instance is unregistered for logging.
-  thread_proxy_->Detach();
+  //thread_proxy_->Detach();
 
   // Unregister this instance so that debug log messages will no longer be sent
   // to it. This will stop all logging in all Chromoting instances.
@@ -175,10 +176,7 @@ ChromotingInstance::~ChromotingInstance() {
   // Stopping the context shuts down all chromoting threads.
   context_.Stop();
 
-  // Delete |thread_proxy_| before we detach |plugin_message_loop_|,
-  // otherwise ScopedThreadProxy may DCHECK when being destroyed.
-  thread_proxy_.reset();
-
+  // Ensure that nothing touches the plugin thread delegate after this point.
   plugin_message_loop_->Detach();
 }
 
@@ -614,7 +612,8 @@ void ChromotingInstance::RegisterLoggingInstance() {
   // and display them to the user.
   // If multiple plugins are run, then the last one registered will handle all
   // logging for all instances.
-  g_logging_instance = this;
+  g_logging_instance = weak_factory_.GetWeakPtr();
+  g_logging_message_loop = plugin_message_loop_;
   g_has_logging_instance = true;
 }
 
@@ -622,12 +621,13 @@ void ChromotingInstance::UnregisterLoggingInstance() {
   base::AutoLock lock(g_logging_lock.Get());
 
   // Don't unregister unless we're the currently registered instance.
-  if (this != g_logging_instance)
+  if (this != g_logging_instance.get())
     return;
 
   // Unregister this instance for logging.
   g_has_logging_instance = false;
-  g_logging_instance = NULL;
+  g_logging_instance.reset();
+  g_logging_message_loop = NULL;
 
   VLOG(1) << "Unregistering global log handler";
 }
@@ -652,21 +652,20 @@ bool ChromotingInstance::LogToUI(int severity, const char* file, int line,
     // Do not LOG anything while holding this lock or else the code will
     // deadlock while trying to re-get the lock we're already in.
     base::AutoLock lock(g_logging_lock.Get());
-    if (g_logging_instance &&
+    if (g_logging_message_loop.get() &&
         // If |g_logging_to_plugin| is set and we're on the logging thread, then
         // this LOG message came from handling a previous LOG message and we
         // should skip it to avoid an infinite loop of LOG messages.
         // We don't have a lock around |g_in_processtoui|, but that's OK since
         // the value is only read/written on the logging thread.
-        (!g_logging_instance->plugin_message_loop_->BelongsToCurrentThread() ||
+        (!g_logging_message_loop->BelongsToCurrentThread() ||

[Sergey Ulanov, 2012/05/29 18:58:30]

Races are still possible in this code. The logging thread may reset
|g_logging_message_loop| after we verify g_logging_message_loop.get() and this
line. One way to solve it is to copy refptr to the stack and then use the copy
here. Or maybe add a lock, then |g_logging_message_loop| wouldn't have to be
global.

[Wez, 2012/05/30 00:18:39]

There is already a lock held at this point (g_logging_lock).  It would make
sense to grab the task runner reference in the lock and log outside it, though.

          !g_logging_to_plugin)) {
       std::string message = remoting::GetTimestampString();
       message += (str.c_str() + message_start);
-      // |thread_proxy_| is safe to use here because we detach it before
-      // tearing down the |g_logging_instance|.
-      g_logging_instance->thread_proxy_->PostTask(
+
+      g_logging_message_loop->PostTask(
           FROM_HERE, base::Bind(&ChromotingInstance::ProcessLogToUI,
-                                base::Unretained(g_logging_instance), message));
+                                g_logging_instance, message));
     }
   }