Bug 1146580 - Make FinalizationWitnessService listen for xpcom shutdown. r=bholley

toolkit/components/build/nsToolkitCompsModule.cpp

@@ -120,7 +120,7 @@ NS_GENERIC_FACTORY_CONSTRUCTOR(nsBrowserStatusFilter)
 #if defined(MOZ_UPDATER) && !defined(MOZ_WIDGET_ANDROID)
 NS_GENERIC_FACTORY_CONSTRUCTOR(nsUpdateProcessor)
 #endif
-NS_GENERIC_FACTORY_CONSTRUCTOR(FinalizationWitnessService)
+NS_GENERIC_FACTORY_CONSTRUCTOR_INIT(FinalizationWitnessService, Init)
 NS_GENERIC_FACTORY_CONSTRUCTOR(NativeOSFileInternalsService)
 NS_GENERIC_FACTORY_CONSTRUCTOR_INIT(NativeFileWatcherService, Init)
 

toolkit/components/finalizationwitness/FinalizationWitnessService.cpp

@@ -18,6 +18,8 @@
 
 // Implementation of nsIFinalizationWitnessService
 
+static bool gShuttingDown = false;
+
 namespace mozilla {
 
 namespace {
@@ -99,8 +101,8 @@ ExtractFinalizationEvent(JSObject *objSelf)
 void Finalize(JSFreeOp *fop, JSObject *objSelf)
 {
   nsRefPtr<FinalizationEvent> event = ExtractFinalizationEvent(objSelf);
-  if (event == nullptr) {
-    // Forget() has been called
+  if (event == nullptr || gShuttingDown) {
+    // NB: event will be null if Forget() has been called
     return;
   }
 
@@ -171,7 +173,7 @@ static const JSFunctionSpec sWitnessClassFunctions[] = {
 
 }
 
-NS_IMPL_ISUPPORTS(FinalizationWitnessService, nsIFinalizationWitnessService)
+NS_IMPL_ISUPPORTS(FinalizationWitnessService, nsIFinalizationWitnessService, nsIObserver)
 
 /**
  * Create a new Finalization Witness.
@@ -209,4 +211,30 @@ FinalizationWitnessService::Make(const char* aTopic,
   return NS_OK;
 }
 
+NS_IMETHODIMP
+FinalizationWitnessService::Observe(nsISupports* aSubject,
+                                    const char* aTopic,
+                                    const char16_t* aValue)
+{
+  MOZ_ASSERT(strcmp(aTopic, NS_XPCOM_SHUTDOWN_OBSERVER_ID) == 0);
+  gShuttingDown = true;
+  nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+  if (obs) {
+    obs->RemoveObserver(this, NS_XPCOM_SHUTDOWN_OBSERVER_ID);
+  }
+
+  return NS_OK;
+}
+
+nsresult
+FinalizationWitnessService::Init()
+{
+  nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+  if (!obs) {
+    return NS_ERROR_FAILURE;
+  }
+
+  return obs->AddObserver(this, NS_XPCOM_SHUTDOWN_OBSERVER_ID, false);
+}
+
 } // namespace mozilla

toolkit/components/finalizationwitness/FinalizationWitnessService.h

@@ -6,17 +6,22 @@
 #define mozilla_finalizationwitnessservice_h__
 
 #include "nsIFinalizationWitnessService.h"
+#include "nsIObserver.h"
 
 namespace mozilla {
 
 /**
  * XPConnect initializer, for use in the main thread.
  */
-class FinalizationWitnessService final : public nsIFinalizationWitnessService
+class FinalizationWitnessService final : public nsIFinalizationWitnessService,
+                                         public nsIObserver
 {
  public:
   NS_DECL_ISUPPORTS
   NS_DECL_NSIFINALIZATIONWITNESSSERVICE
+  NS_DECL_NSIOBSERVER
+
+  nsresult Init();
  private:
   ~FinalizationWitnessService() {}
   void operator=(const FinalizationWitnessService* other) = delete;