Bug 498010 - Threads should release their observers when they are shut down; r=benjamin

xpcom/threads/nsIThreadInternal.idl

@@ -51,7 +51,9 @@ interface nsIThreadInternal : nsIThread
   /**
    * Get/set the current thread observer (may be null).  This attribute may be
    * read from any thread, but must only be set on the thread corresponding to
-   * this thread object.
+   * this thread object.  The observer will be released on the thread
+   * corresponding to this thread object after all other events have been
+   * processed during a call to Shutdown.
    */
   attribute nsIThreadObserver observer;
 

xpcom/threads/nsThread.cpp

@@ -280,6 +280,9 @@ nsThread::ThreadFunc(void *arg)
   event = new nsThreadShutdownAckEvent(self->mShutdownContext);
   self->mShutdownContext->joiningThread->Dispatch(event, NS_DISPATCH_NORMAL);
 
+  // Release any observer of the thread here.
+  self->SetObserver(nsnull);
+
   NS_RELEASE(self);
 }
 
@@ -468,6 +471,14 @@ nsThread::Shutdown()
 
   PR_JoinThread(mThread);
   mThread = nsnull;
+
+#ifdef DEBUG
+  {
+    nsAutoLock lock(mLock);
+    NS_ASSERTION(!mObserver, "Should have been cleared at shutdown!");
+  }
+#endif
+
   return NS_OK;
 }
 

xpcom/threads/nsThreadManager.cpp

@@ -155,6 +155,11 @@ nsThreadManager::Shutdown()
     mThreadsByPRThread.Clear();
   }
 
+  // Normally thread shutdown clears the observer for the thread, but since the
+  // main thread is special we do it manually here after we're sure all events
+  // have been processed.
+  mMainThread->SetObserver(nsnull);
+
   // Release main thread object.
   mMainThread = nsnull;