Make ObserverListThreadSafe key its observers by PlatformThreadId instead of MessageLoop.

base/observer_list_threadsafe.h

 // 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.
 
 #ifndef BASE_OBSERVER_LIST_THREADSAFE_H_
 #define BASE_OBSERVER_LIST_THREADSAFE_H_
 #pragma once
 
 #include <algorithm>
 #include <map>
 
 #include "base/basictypes.h"
 #include "base/bind.h"
 #include "base/callback_old.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/memory/ref_counted.h"
 #include "base/message_loop.h"
 #include "base/message_loop_proxy.h"
 #include "base/observer_list.h"
 #include "base/task.h"
+#include "base/threading/platform_thread.h"
 
 ///////////////////////////////////////////////////////////////////////////////
 //
 // OVERVIEW:
 //
 //   A thread-safe container for a list of observers.
 //   This is similar to the observer_list (see observer_list.h), but it
 //   is more robust for multi-threaded situations.
 //
 //   The following use cases are supported:
@@ skipping 50 matching lines @@
   typedef typename ObserverList<ObserverType>::NotificationType
       NotificationType;
 
   ObserverListThreadSafe()
       : type_(ObserverListBase<ObserverType>::NOTIFY_ALL) {}
   explicit ObserverListThreadSafe(NotificationType type) : type_(type) {}
 
   // Add an observer to the list.  An observer should not be added to
   // the same list more than once.
   void AddObserver(ObserverType* obs) {
+    // If there is not a current MessageLoop, it is impossible to notify on it,
+    // so do not add the observer.
+    if (!MessageLoop::current())
+      return;
+
     ObserverList<ObserverType>* list = NULL;
-    MessageLoop* loop = MessageLoop::current();
-    // TODO(mbelshe): Get rid of this check.  Its needed right now because
-    //                Time currently triggers usage of the ObserverList.
-    //                And unittests use time without a MessageLoop.
-    if (!loop)
-      return;  // Some unittests may access this without a message loop.
+    base::PlatformThreadId thread_id = base::PlatformThread::CurrentId();
     {
       base::AutoLock lock(list_lock_);
-      if (observer_lists_.find(loop) == observer_lists_.end())
-        observer_lists_[loop] = new ObserverListContext(type_);
-      list = &(observer_lists_[loop]->list);
+      if (observer_lists_.find(thread_id) == observer_lists_.end())
+        observer_lists_[thread_id] = new ObserverListContext(type_);
+      list = &(observer_lists_[thread_id]->list);
     }
     list->AddObserver(obs);
   }
 
   // Remove an observer from the list if it is in the list.
   // If there are pending notifications in-transit to the observer, they will
   // be aborted.
   // If the observer to be removed is in the list, RemoveObserver MUST
   // be called from the same thread which called AddObserver.
   void RemoveObserver(ObserverType* obs) {
     ObserverListContext* context = NULL;
     ObserverList<ObserverType>* list = NULL;
-    MessageLoop* loop = MessageLoop::current();
-    if (!loop)
-      return;  // On shutdown, it is possible that current() is already null.
+    base::PlatformThreadId thread_id = base::PlatformThread::CurrentId();
     {
       base::AutoLock lock(list_lock_);
-      typename ObserversListMap::iterator it = observer_lists_.find(loop);
+      typename ObserversListMap::iterator it = observer_lists_.find(thread_id);
       if (it == observer_lists_.end()) {
         // This will happen if we try to remove an observer on a thread
         // we never added an observer for.
         return;
       }
       context = it->second;
       list = &context->list;
 
       // If we're about to remove the last observer from the list,
       // then we can remove this observer_list entirely.
@@ skipping 89 matching lines @@
   // ObserverList.  This function MUST be called on the thread which owns
   // the unsafe ObserverList.
   template <class Method, class Params>
   void NotifyWrapper(ObserverListContext* context,
       const UnboundMethod<ObserverType, Method, Params>& method) {
 
     // Check that this list still needs notifications.
     {
       base::AutoLock lock(list_lock_);
       typename ObserversListMap::iterator it =
-          observer_lists_.find(MessageLoop::current());
+          observer_lists_.find(base::PlatformThread::CurrentId());
 
       // The ObserverList could have been removed already.  In fact, it could
       // have been removed and then re-added!  If the master list's loop
       // does not match this one, then we do not need to finish this
       // notification.
       if (it == observer_lists_.end() || it->second != context)
         return;
     }
 
     {
       typename ObserverList<ObserverType>::Iterator it(context->list);
       ObserverType* obs;
       while ((obs = it.GetNext()) != NULL)
         method.Run(obs);
     }
 
     // If there are no more observers on the list, we can now delete it.
     if (context->list.size() == 0) {
       {
         base::AutoLock lock(list_lock_);
         // Remove |list| if it's not already removed.
         // This can happen if multiple observers got removed in a notification.
         // See http://crbug.com/55725.
         typename ObserversListMap::iterator it =
-            observer_lists_.find(MessageLoop::current());
+            observer_lists_.find(base::PlatformThread::CurrentId());
         if (it != observer_lists_.end() && it->second == context)
           observer_lists_.erase(it);
       }
       delete context;
     }
   }
 
-  typedef std::map<MessageLoop*, ObserverListContext*> ObserversListMap;
+  // Key by PlatformThreadId because in tests, clients can attempt to remove
+  // observers without a MessageLoop. If this were keyed by MessageLoop, that
+  // operation would be silently ignored, leaving garbage in the ObserverList.
+  typedef std::map<base::PlatformThreadId, ObserverListContext*>
+      ObserversListMap;
 
   base::Lock list_lock_;  // Protects the observer_lists_.
   ObserversListMap observer_lists_;
   const NotificationType type_;
 
   DISALLOW_COPY_AND_ASSIGN(ObserverListThreadSafe);
 };
 
 #endif  // BASE_OBSERVER_LIST_THREADSAFE_H_