1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/toolkit/components/finalizationwitness/FinalizationWitnessService.cpp Wed Dec 31 06:09:35 2014 +0100
1.3 @@ -0,0 +1,213 @@
1.4 +/* This Source Code Form is subject to the terms of the Mozilla Public
1.5 + * License, v. 2.0. If a copy of the MPL was not distributed with this file,
1.6 + * You can obtain one at http://mozilla.org/MPL/2.0/. */
1.7 +
1.8 +#include "FinalizationWitnessService.h"
1.9 +
1.10 +#include "nsString.h"
1.11 +#include "jsapi.h"
1.12 +#include "js/CallNonGenericMethod.h"
1.13 +#include "mozJSComponentLoader.h"
1.14 +#include "nsZipArchive.h"
1.15 +
1.16 +#include "mozilla/Scoped.h"
1.17 +#include "mozilla/Services.h"
1.18 +#include "mozilla/NullPtr.h"
1.19 +#include "nsIObserverService.h"
1.20 +#include "nsThreadUtils.h"
1.21 +
1.22 +
1.23 +// Implementation of nsIFinalizationWitnessService
1.24 +
1.25 +namespace mozilla {
1.26 +
1.27 +namespace {
1.28 +
1.29 +/**
1.30 + * An event meant to be dispatched to the main thread upon finalization
1.31 + * of a FinalizationWitness, unless method |forget()| has been called.
1.32 + *
1.33 + * Held as private data by each instance of FinalizationWitness.
1.34 + * Important note: we maintain the invariant that these private data
1.35 + * slots are already addrefed.
1.36 + */
1.37 +class FinalizationEvent MOZ_FINAL: public nsRunnable
1.38 +{
1.39 +public:
1.40 + FinalizationEvent(const char* aTopic,
1.41 + const jschar* aValue)
1.42 + : mTopic(aTopic)
1.43 + , mValue(aValue)
1.44 + { }
1.45 +
1.46 + NS_METHOD Run() {
1.47 + nsCOMPtr<nsIObserverService> observerService =
1.48 + mozilla::services::GetObserverService();
1.49 + if (!observerService) {
1.50 + // This is either too early or, more likely, too late for notifications.
1.51 + // Bail out.
1.52 + return NS_ERROR_NOT_AVAILABLE;
1.53 + }
1.54 + (void)observerService->
1.55 + NotifyObservers(nullptr, mTopic.get(), mValue.get());
1.56 + return NS_OK;
1.57 + }
1.58 +private:
1.59 + /**
1.60 + * The topic on which to broadcast the notification of finalization.
1.61 + *
1.62 + * Deallocated on the main thread.
1.63 + */
1.64 + const nsCString mTopic;
1.65 +
1.66 + /**
1.67 + * The result of converting the exception to a string.
1.68 + *
1.69 + * Deallocated on the main thread.
1.70 + */
1.71 + const nsString mValue;
1.72 +};
1.73 +
1.74 +enum {
1.75 + WITNESS_SLOT_EVENT,
1.76 + WITNESS_INSTANCES_SLOTS
1.77 +};
1.78 +
1.79 +/**
1.80 + * Extract the FinalizationEvent from an instance of FinalizationWitness
1.81 + * and clear the slot containing the FinalizationEvent.
1.82 + */
1.83 +already_AddRefed<FinalizationEvent>
1.84 +ExtractFinalizationEvent(JSObject *objSelf)
1.85 +{
1.86 + JS::Value slotEvent = JS_GetReservedSlot(objSelf, WITNESS_SLOT_EVENT);
1.87 + if (slotEvent.isUndefined()) {
1.88 + // Forget() has been called
1.89 + return nullptr;
1.90 + }
1.91 +
1.92 + JS_SetReservedSlot(objSelf, WITNESS_SLOT_EVENT, JS::UndefinedValue());
1.93 +
1.94 + return dont_AddRef(static_cast<FinalizationEvent*>(slotEvent.toPrivate()));
1.95 +}
1.96 +
1.97 +/**
1.98 + * Finalizer for instances of FinalizationWitness.
1.99 + *
1.100 + * Unless method Forget() has been called, the finalizer displays an error
1.101 + * message.
1.102 + */
1.103 +void Finalize(JSFreeOp *fop, JSObject *objSelf)
1.104 +{
1.105 + nsRefPtr<FinalizationEvent> event = ExtractFinalizationEvent(objSelf);
1.106 + if (event == nullptr) {
1.107 + // Forget() has been called
1.108 + return;
1.109 + }
1.110 +
1.111 + // Notify observers. Since we are executed during garbage-collection,
1.112 + // we need to dispatch the notification to the main thread.
1.113 + (void)NS_DispatchToMainThread(event);
1.114 + // We may fail at dispatching to the main thread if we arrive too late
1.115 + // during shutdown. In that case, there is not much we can do.
1.116 +}
1.117 +
1.118 +static const JSClass sWitnessClass = {
1.119 + "FinalizationWitness",
1.120 + JSCLASS_HAS_RESERVED_SLOTS(WITNESS_INSTANCES_SLOTS),
1.121 + JS_PropertyStub /* addProperty */,
1.122 + JS_DeletePropertyStub /* delProperty */,
1.123 + JS_PropertyStub /* getProperty */,
1.124 + JS_StrictPropertyStub /* setProperty */,
1.125 + JS_EnumerateStub /* enumerate */,
1.126 + JS_ResolveStub /* resolve */,
1.127 + JS_ConvertStub /* convert */,
1.128 + Finalize /* finalize */
1.129 +};
1.130 +
1.131 +bool IsWitness(JS::Handle<JS::Value> v)
1.132 +{
1.133 + return v.isObject() && JS_GetClass(&v.toObject()) == &sWitnessClass;
1.134 +}
1.135 +
1.136 +
1.137 +/**
1.138 + * JS method |forget()|
1.139 + *
1.140 + * === JS documentation
1.141 + *
1.142 + * Neutralize the witness. Once this method is called, the witness will
1.143 + * never report any error.
1.144 + */
1.145 +bool ForgetImpl(JSContext* cx, JS::CallArgs args)
1.146 +{
1.147 + if (args.length() != 0) {
1.148 + JS_ReportError(cx, "forget() takes no arguments");
1.149 + return false;
1.150 + }
1.151 + JS::Rooted<JS::Value> valSelf(cx, args.thisv());
1.152 + JS::Rooted<JSObject*> objSelf(cx, &valSelf.toObject());
1.153 +
1.154 + nsRefPtr<FinalizationEvent> event = ExtractFinalizationEvent(objSelf);
1.155 + if (event == nullptr) {
1.156 + JS_ReportError(cx, "forget() called twice");
1.157 + return false;
1.158 + }
1.159 +
1.160 + args.rval().setUndefined();
1.161 + return true;
1.162 +}
1.163 +
1.164 +bool Forget(JSContext *cx, unsigned argc, JS::Value *vp)
1.165 +{
1.166 + JS::CallArgs args = CallArgsFromVp(argc, vp);
1.167 + return JS::CallNonGenericMethod<IsWitness, ForgetImpl>(cx, args);
1.168 +}
1.169 +
1.170 +static const JSFunctionSpec sWitnessClassFunctions[] = {
1.171 + JS_FN("forget", Forget, 0, JSPROP_READONLY | JSPROP_PERMANENT),
1.172 + JS_FS_END
1.173 +};
1.174 +
1.175 +}
1.176 +
1.177 +NS_IMPL_ISUPPORTS(FinalizationWitnessService, nsIFinalizationWitnessService)
1.178 +
1.179 +/**
1.180 + * Create a new Finalization Witness.
1.181 + *
1.182 + * A finalization witness is an object whose sole role is to notify
1.183 + * observers when it is gc-ed. Once the witness is created, call its
1.184 + * method |forget()| to prevent the observers from being notified.
1.185 + *
1.186 + * @param aTopic The notification topic.
1.187 + * @param aValue The notification value. Converted to a string.
1.188 + *
1.189 + * @constructor
1.190 + */
1.191 +NS_IMETHODIMP
1.192 +FinalizationWitnessService::Make(const char* aTopic,
1.193 + const char16_t* aValue,
1.194 + JSContext* aCx,
1.195 + JS::MutableHandle<JS::Value> aRetval)
1.196 +{
1.197 + JS::Rooted<JSObject*> objResult(aCx, JS_NewObject(aCx, &sWitnessClass, JS::NullPtr(),
1.198 + JS::NullPtr()));
1.199 + if (!objResult) {
1.200 + return NS_ERROR_OUT_OF_MEMORY;
1.201 + }
1.202 + if (!JS_DefineFunctions(aCx, objResult, sWitnessClassFunctions)) {
1.203 + return NS_ERROR_FAILURE;
1.204 + }
1.205 +
1.206 + nsRefPtr<FinalizationEvent> event = new FinalizationEvent(aTopic, aValue);
1.207 +
1.208 + // Transfer ownership of the addrefed |event| to |objResult|.
1.209 + JS_SetReservedSlot(objResult, WITNESS_SLOT_EVENT,
1.210 + JS::PrivateValue(event.forget().take()));
1.211 +
1.212 + aRetval.setObject(*objResult);
1.213 + return NS_OK;
1.214 +}
1.215 +
1.216 +} // namespace mozilla
