Bug 830125 - Add the preferences memory reporter off a runnable, so as to avoid recursive GetService calls. r=njn

modules/libpref/src/Preferences.cpp

@@ -177,6 +177,8 @@ SizeOfObserverEntryExcludingThis(ValueObserverHashKey* aKey,
 int64_t
 Preferences::GetPreferencesMemoryUsed()
 {
+  NS_ENSURE_TRUE(InitStaticMembers(), 0);
+
   size_t n = 0;
   n += PreferencesMallocSizeOf(sPreferences);
   if (gHashTable.ops) {
@@ -209,6 +211,18 @@ NS_MEMORY_REPORTER_IMPLEMENT(Preferences,
   Preferences::GetPreferencesMemoryUsed,
   "Memory used by the preferences system.")
 
+namespace {
+class AddPreferencesMemoryReporterRunnable : public nsRunnable
+{
+  NS_IMETHOD Run()
+  {
+    nsCOMPtr<nsIMemoryReporter> reporter =
+      new NS_MEMORY_REPORTER_NAME(Preferences);
+    return NS_RegisterMemoryReporter(reporter);
+  }
+};
+} // anonymous namespace
+
 // static
 Preferences*
 Preferences::GetInstanceForService()
@@ -239,8 +253,13 @@ Preferences::GetInstanceForService()
   gObserverTable = new nsRefPtrHashtable<ValueObserverHashKey, ValueObserver>();
   gObserverTable->Init();
 
-  nsCOMPtr<nsIMemoryReporter> reporter(new NS_MEMORY_REPORTER_NAME(Preferences));
-  NS_RegisterMemoryReporter(reporter);
+  // Preferences;:GetInstanceForService() can be called from GetService(), and
+  // NS_RegisterMemoryReporter calls GetService(nsIMemoryReporter).  To avoid a
+  // potential recursive GetService() call, we can't register the memory
+  // reporter here; instead, do it off a runnable.
+  nsRefPtr<AddPreferencesMemoryReporterRunnable> runnable =
+    new AddPreferencesMemoryReporterRunnable();
+  NS_DispatchToMainThread(runnable);
 
   NS_ADDREF(sPreferences);
   return sPreferences;