michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
michael@0:  * You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: #include "FinalizationWitnessService.h"
michael@0: 
michael@0: #include "nsString.h"
michael@0: #include "jsapi.h"
michael@0: #include "js/CallNonGenericMethod.h"
michael@0: #include "mozJSComponentLoader.h"
michael@0: #include "nsZipArchive.h"
michael@0: 
michael@0: #include "mozilla/Scoped.h"
michael@0: #include "mozilla/Services.h"
michael@0: #include "mozilla/NullPtr.h"
michael@0: #include "nsIObserverService.h"
michael@0: #include "nsThreadUtils.h"
michael@0: 
michael@0: 
michael@0: // Implementation of nsIFinalizationWitnessService
michael@0: 
michael@0: namespace mozilla {
michael@0: 
michael@0: namespace {
michael@0: 
michael@0: /**
michael@0:  * An event meant to be dispatched to the main thread upon finalization
michael@0:  * of a FinalizationWitness, unless method |forget()| has been called.
michael@0:  *
michael@0:  * Held as private data by each instance of FinalizationWitness.
michael@0:  * Important note: we maintain the invariant that these private data
michael@0:  * slots are already addrefed.
michael@0:  */
michael@0: class FinalizationEvent MOZ_FINAL: public nsRunnable
michael@0: {
michael@0: public:
michael@0:   FinalizationEvent(const char* aTopic,
michael@0:                   const jschar* aValue)
michael@0:     : mTopic(aTopic)
michael@0:     , mValue(aValue)
michael@0:   { }
michael@0: 
michael@0:   NS_METHOD Run() {
michael@0:     nsCOMPtr<nsIObserverService> observerService =
michael@0:       mozilla::services::GetObserverService();
michael@0:     if (!observerService) {
michael@0:       // This is either too early or, more likely, too late for notifications.
michael@0:       // Bail out.
michael@0:       return NS_ERROR_NOT_AVAILABLE;
michael@0:     }
michael@0:     (void)observerService->
michael@0:       NotifyObservers(nullptr, mTopic.get(), mValue.get());
michael@0:     return NS_OK;
michael@0:   }
michael@0: private:
michael@0:   /**
michael@0:    * The topic on which to broadcast the notification of finalization.
michael@0:    *
michael@0:    * Deallocated on the main thread.
michael@0:    */
michael@0:   const nsCString mTopic;
michael@0: 
michael@0:   /**
michael@0:    * The result of converting the exception to a string.
michael@0:    *
michael@0:    * Deallocated on the main thread.
michael@0:    */
michael@0:   const nsString mValue;
michael@0: };
michael@0: 
michael@0: enum {
michael@0:   WITNESS_SLOT_EVENT,
michael@0:   WITNESS_INSTANCES_SLOTS
michael@0: };
michael@0: 
michael@0: /**
michael@0:  * Extract the FinalizationEvent from an instance of FinalizationWitness
michael@0:  * and clear the slot containing the FinalizationEvent.
michael@0:  */
michael@0: already_AddRefed<FinalizationEvent>
michael@0: ExtractFinalizationEvent(JSObject *objSelf)
michael@0: {
michael@0:   JS::Value slotEvent = JS_GetReservedSlot(objSelf, WITNESS_SLOT_EVENT);
michael@0:   if (slotEvent.isUndefined()) {
michael@0:     // Forget() has been called
michael@0:     return nullptr;
michael@0:   }
michael@0: 
michael@0:   JS_SetReservedSlot(objSelf, WITNESS_SLOT_EVENT, JS::UndefinedValue());
michael@0: 
michael@0:   return dont_AddRef(static_cast<FinalizationEvent*>(slotEvent.toPrivate()));
michael@0: }
michael@0: 
michael@0: /**
michael@0:  * Finalizer for instances of FinalizationWitness.
michael@0:  *
michael@0:  * Unless method Forget() has been called, the finalizer displays an error
michael@0:  * message.
michael@0:  */
michael@0: void Finalize(JSFreeOp *fop, JSObject *objSelf)
michael@0: {
michael@0:   nsRefPtr<FinalizationEvent> event = ExtractFinalizationEvent(objSelf);
michael@0:   if (event == nullptr) {
michael@0:     // Forget() has been called
michael@0:     return;
michael@0:   }
michael@0: 
michael@0:   // Notify observers. Since we are executed during garbage-collection,
michael@0:   // we need to dispatch the notification to the main thread.
michael@0:   (void)NS_DispatchToMainThread(event);
michael@0:   // We may fail at dispatching to the main thread if we arrive too late
michael@0:   // during shutdown. In that case, there is not much we can do.
michael@0: }
michael@0: 
michael@0: static const JSClass sWitnessClass = {
michael@0:   "FinalizationWitness",
michael@0:   JSCLASS_HAS_RESERVED_SLOTS(WITNESS_INSTANCES_SLOTS),
michael@0:   JS_PropertyStub /* addProperty */,
michael@0:   JS_DeletePropertyStub /* delProperty */,
michael@0:   JS_PropertyStub /* getProperty */,
michael@0:   JS_StrictPropertyStub /* setProperty */,
michael@0:   JS_EnumerateStub /* enumerate */,
michael@0:   JS_ResolveStub /* resolve */,
michael@0:   JS_ConvertStub /* convert */,
michael@0:   Finalize /* finalize */
michael@0: };
michael@0: 
michael@0: bool IsWitness(JS::Handle<JS::Value> v)
michael@0: {
michael@0:   return v.isObject() && JS_GetClass(&v.toObject()) == &sWitnessClass;
michael@0: }
michael@0: 
michael@0: 
michael@0: /**
michael@0:  * JS method |forget()|
michael@0:  *
michael@0:  * === JS documentation
michael@0:  *
michael@0:  *  Neutralize the witness. Once this method is called, the witness will
michael@0:  *  never report any error.
michael@0:  */
michael@0: bool ForgetImpl(JSContext* cx, JS::CallArgs args)
michael@0: {
michael@0:   if (args.length() != 0) {
michael@0:     JS_ReportError(cx, "forget() takes no arguments");
michael@0:     return false;
michael@0:   }
michael@0:   JS::Rooted<JS::Value> valSelf(cx, args.thisv());
michael@0:   JS::Rooted<JSObject*> objSelf(cx, &valSelf.toObject());
michael@0: 
michael@0:   nsRefPtr<FinalizationEvent> event = ExtractFinalizationEvent(objSelf);
michael@0:   if (event == nullptr) {
michael@0:     JS_ReportError(cx, "forget() called twice");
michael@0:     return false;
michael@0:   }
michael@0: 
michael@0:   args.rval().setUndefined();
michael@0:   return true;
michael@0: }
michael@0: 
michael@0: bool Forget(JSContext *cx, unsigned argc, JS::Value *vp)
michael@0: {
michael@0:   JS::CallArgs args = CallArgsFromVp(argc, vp);
michael@0:   return JS::CallNonGenericMethod<IsWitness, ForgetImpl>(cx, args);
michael@0: }
michael@0: 
michael@0: static const JSFunctionSpec sWitnessClassFunctions[] = {
michael@0:   JS_FN("forget", Forget, 0, JSPROP_READONLY | JSPROP_PERMANENT),
michael@0:   JS_FS_END
michael@0: };
michael@0: 
michael@0: }
michael@0: 
michael@0: NS_IMPL_ISUPPORTS(FinalizationWitnessService, nsIFinalizationWitnessService)
michael@0: 
michael@0: /**
michael@0:  * Create a new Finalization Witness.
michael@0:  *
michael@0:  * A finalization witness is an object whose sole role is to notify
michael@0:  * observers when it is gc-ed. Once the witness is created, call its
michael@0:  * method |forget()| to prevent the observers from being notified.
michael@0:  *
michael@0:  * @param aTopic The notification topic.
michael@0:  * @param aValue The notification value. Converted to a string.
michael@0:  *
michael@0:  * @constructor
michael@0:  */
michael@0: NS_IMETHODIMP
michael@0: FinalizationWitnessService::Make(const char* aTopic,
michael@0:                                  const char16_t* aValue,
michael@0:                                  JSContext* aCx,
michael@0:                                  JS::MutableHandle<JS::Value> aRetval)
michael@0: {
michael@0:   JS::Rooted<JSObject*> objResult(aCx, JS_NewObject(aCx, &sWitnessClass, JS::NullPtr(),
michael@0:                                                     JS::NullPtr()));
michael@0:   if (!objResult) {
michael@0:     return NS_ERROR_OUT_OF_MEMORY;
michael@0:   }
michael@0:   if (!JS_DefineFunctions(aCx, objResult, sWitnessClassFunctions)) {
michael@0:     return NS_ERROR_FAILURE;
michael@0:   }
michael@0: 
michael@0:   nsRefPtr<FinalizationEvent> event = new FinalizationEvent(aTopic, aValue);
michael@0: 
michael@0:   // Transfer ownership of the addrefed |event| to |objResult|.
michael@0:   JS_SetReservedSlot(objResult, WITNESS_SLOT_EVENT,
michael@0:                      JS::PrivateValue(event.forget().take()));
michael@0: 
michael@0:   aRetval.setObject(*objResult);
michael@0:   return NS_OK;
michael@0: }
michael@0: 
michael@0: } // namespace mozilla