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-rw-r--r--dom/media/MediaEventSource.h594
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diff --git a/dom/media/MediaEventSource.h b/dom/media/MediaEventSource.h
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+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef MediaEventSource_h_
+#define MediaEventSource_h_
+
+#include <type_traits>
+#include <utility>
+
+#include "mozilla/AbstractThread.h"
+#include "mozilla/Atomics.h"
+#include "mozilla/DataMutex.h"
+#include "mozilla/Mutex.h"
+
+#include "mozilla/Unused.h"
+
+#include "nsISupportsImpl.h"
+#include "nsTArray.h"
+#include "nsThreadUtils.h"
+
+namespace mozilla {
+
+/**
+ * A thread-safe tool to communicate "revocation" across threads. It is used to
+ * disconnect a listener from the event source to prevent future notifications
+ * from coming. Revoke() can be called on any thread. However, it is recommended
+ * to be called on the target thread to avoid race condition.
+ *
+ * RevocableToken is not exposed to the client code directly.
+ * Use MediaEventListener below to do the job.
+ */
+class RevocableToken {
+ NS_INLINE_DECL_THREADSAFE_REFCOUNTING(RevocableToken);
+
+ public:
+ RevocableToken() = default;
+
+ virtual void Revoke() = 0;
+ virtual bool IsRevoked() const = 0;
+
+ protected:
+ // Virtual destructor is required since we might delete a Listener object
+ // through its base type pointer.
+ virtual ~RevocableToken() = default;
+};
+
+enum class ListenerPolicy : int8_t {
+ // Allow at most one listener. Move will be used when possible
+ // to pass the event data to save copy.
+ Exclusive,
+ // Allow multiple listeners. Event data will always be copied when passed
+ // to the listeners.
+ NonExclusive
+};
+
+namespace detail {
+
+/**
+ * Define how an event type is passed internally in MediaEventSource and to the
+ * listeners. Specialized for the void type to pass a dummy bool instead.
+ */
+template <typename T>
+struct EventTypeTraits {
+ typedef T ArgType;
+};
+
+template <>
+struct EventTypeTraits<void> {
+ typedef bool ArgType;
+};
+
+/**
+ * Test if a method function or lambda accepts one or more arguments.
+ */
+template <typename T>
+class TakeArgsHelper {
+ template <typename C>
+ static std::false_type test(void (C::*)(), int);
+ template <typename C>
+ static std::false_type test(void (C::*)() const, int);
+ template <typename C>
+ static std::false_type test(void (C::*)() volatile, int);
+ template <typename C>
+ static std::false_type test(void (C::*)() const volatile, int);
+ template <typename F>
+ static std::false_type test(F&&, decltype(std::declval<F>()(), 0));
+ static std::true_type test(...);
+
+ public:
+ typedef decltype(test(std::declval<T>(), 0)) type;
+};
+
+template <typename T>
+struct TakeArgs : public TakeArgsHelper<T>::type {};
+
+template <typename T>
+struct EventTarget;
+
+template <>
+struct EventTarget<nsIEventTarget> {
+ static void Dispatch(nsIEventTarget* aTarget,
+ already_AddRefed<nsIRunnable> aTask) {
+ aTarget->Dispatch(std::move(aTask), NS_DISPATCH_NORMAL);
+ }
+ static bool IsOnTargetThread(nsIEventTarget* aTarget) {
+ bool rv;
+ aTarget->IsOnCurrentThread(&rv);
+ return rv;
+ }
+};
+
+template <>
+struct EventTarget<AbstractThread> {
+ static void Dispatch(AbstractThread* aTarget,
+ already_AddRefed<nsIRunnable> aTask) {
+ aTarget->Dispatch(std::move(aTask));
+ }
+ static bool IsOnTargetThread(AbstractThread* aTarget) {
+ bool rv;
+ aTarget->IsOnCurrentThread(&rv);
+ return rv;
+ }
+};
+
+/**
+ * Encapsulate a raw pointer to be captured by a lambda without causing
+ * static-analysis errors.
+ */
+template <typename T>
+class RawPtr {
+ public:
+ explicit RawPtr(T* aPtr) : mPtr(aPtr) {}
+ T* get() const { return mPtr; }
+
+ private:
+ T* const mPtr;
+};
+
+template <typename... As>
+class Listener : public RevocableToken {
+ public:
+ template <typename... Ts>
+ void Dispatch(Ts&&... aEvents) {
+ if (CanTakeArgs()) {
+ DispatchTask(NewRunnableMethod<std::decay_t<Ts>&&...>(
+ "detail::Listener::ApplyWithArgs", this, &Listener::ApplyWithArgs,
+ std::forward<Ts>(aEvents)...));
+ } else {
+ DispatchTask(NewRunnableMethod("detail::Listener::ApplyWithNoArgs", this,
+ &Listener::ApplyWithNoArgs));
+ }
+ }
+
+ private:
+ virtual void DispatchTask(already_AddRefed<nsIRunnable> aTask) = 0;
+
+ // True if the underlying listener function takes non-zero arguments.
+ virtual bool CanTakeArgs() const = 0;
+ // Pass the event data to the underlying listener function. Should be called
+ // only when CanTakeArgs() returns true.
+ virtual void ApplyWithArgs(As&&... aEvents) = 0;
+ // Invoke the underlying listener function. Should be called only when
+ // CanTakeArgs() returns false.
+ virtual void ApplyWithNoArgs() = 0;
+};
+
+/**
+ * Store the registered target thread and function so it knows where and to
+ * whom to send the event data.
+ */
+template <typename Target, typename Function, typename... As>
+class ListenerImpl : public Listener<As...> {
+ // Strip CV and reference from Function.
+ using FunctionStorage = std::decay_t<Function>;
+ using SelfType = ListenerImpl<Target, Function, As...>;
+
+ public:
+ ListenerImpl(Target* aTarget, Function&& aFunction)
+ : mData(MakeRefPtr<Data>(aTarget, std::forward<Function>(aFunction)),
+ "MediaEvent ListenerImpl::mData") {
+ MOZ_DIAGNOSTIC_ASSERT(aTarget);
+ }
+
+ protected:
+ virtual ~ListenerImpl() {
+ MOZ_ASSERT(IsRevoked(), "Must disconnect the listener.");
+ }
+
+ private:
+ void DispatchTask(already_AddRefed<nsIRunnable> aTask) override {
+ RefPtr<Data> data;
+ {
+ auto d = mData.Lock();
+ data = *d;
+ }
+ if (NS_WARN_IF(!data)) {
+ // already_AddRefed doesn't allow releasing the ref, so transfer it first.
+ RefPtr<nsIRunnable> temp(aTask);
+ return;
+ }
+ EventTarget<Target>::Dispatch(data->mTarget, std::move(aTask));
+ }
+
+ bool CanTakeArgs() const override { return TakeArgs<FunctionStorage>::value; }
+
+ // |F| takes one or more arguments.
+ template <typename F>
+ std::enable_if_t<TakeArgs<F>::value, void> ApplyWithArgsImpl(
+ Target* aTarget, const F& aFunc, As&&... aEvents) {
+ MOZ_DIAGNOSTIC_ASSERT(EventTarget<Target>::IsOnTargetThread(aTarget));
+ aFunc(std::move(aEvents)...);
+ }
+
+ // |F| takes no arguments.
+ template <typename F>
+ std::enable_if_t<!TakeArgs<F>::value, void> ApplyWithArgsImpl(
+ Target* aTarget, const F& aFunc, As&&... aEvents) {
+ MOZ_CRASH("Call ApplyWithNoArgs instead.");
+ }
+
+ void ApplyWithArgs(As&&... aEvents) override {
+ MOZ_RELEASE_ASSERT(TakeArgs<Function>::value);
+ // Don't call the listener if it is disconnected.
+ RefPtr<Data> data;
+ {
+ auto d = mData.Lock();
+ data = *d;
+ }
+ if (!data) {
+ return;
+ }
+ MOZ_DIAGNOSTIC_ASSERT(EventTarget<Target>::IsOnTargetThread(data->mTarget));
+ ApplyWithArgsImpl(data->mTarget, data->mFunction, std::move(aEvents)...);
+ }
+
+ // |F| takes one or more arguments.
+ template <typename F>
+ std::enable_if_t<TakeArgs<F>::value, void> ApplyWithNoArgsImpl(
+ Target* aTarget, const F& aFunc) {
+ MOZ_CRASH("Call ApplyWithArgs instead.");
+ }
+
+ // |F| takes no arguments.
+ template <typename F>
+ std::enable_if_t<!TakeArgs<F>::value, void> ApplyWithNoArgsImpl(
+ Target* aTarget, const F& aFunc) {
+ MOZ_DIAGNOSTIC_ASSERT(EventTarget<Target>::IsOnTargetThread(aTarget));
+ aFunc();
+ }
+
+ void ApplyWithNoArgs() override {
+ MOZ_RELEASE_ASSERT(!TakeArgs<Function>::value);
+ // Don't call the listener if it is disconnected.
+ RefPtr<Data> data;
+ {
+ auto d = mData.Lock();
+ data = *d;
+ }
+ if (!data) {
+ return;
+ }
+ MOZ_DIAGNOSTIC_ASSERT(EventTarget<Target>::IsOnTargetThread(data->mTarget));
+ ApplyWithNoArgsImpl(data->mTarget, data->mFunction);
+ }
+
+ void Revoke() override {
+ {
+ auto data = mData.Lock();
+ *data = nullptr;
+ }
+ }
+
+ bool IsRevoked() const override {
+ auto data = mData.Lock();
+ return !*data;
+ }
+
+ struct RefCountedMediaEventListenerData {
+ // Keep ref-counting here since Data holds a template member, leading to
+ // instances of varying size, which the memory leak logging system dislikes.
+ NS_INLINE_DECL_THREADSAFE_REFCOUNTING(RefCountedMediaEventListenerData)
+ protected:
+ virtual ~RefCountedMediaEventListenerData() = default;
+ };
+ struct Data : public RefCountedMediaEventListenerData {
+ Data(RefPtr<Target> aTarget, Function&& aFunction)
+ : mTarget(std::move(aTarget)),
+ mFunction(std::forward<Function>(aFunction)) {}
+ const RefPtr<Target> mTarget;
+ FunctionStorage mFunction;
+ };
+
+ // Storage for target and function. Also used to track revocation.
+ mutable DataMutex<RefPtr<Data>> mData;
+};
+
+/**
+ * Return true if any type is a reference type.
+ */
+template <typename Head, typename... Tails>
+struct IsAnyReference {
+ static const bool value =
+ std::is_reference_v<Head> || IsAnyReference<Tails...>::value;
+};
+
+template <typename T>
+struct IsAnyReference<T> {
+ static const bool value = std::is_reference_v<T>;
+};
+
+} // namespace detail
+
+template <ListenerPolicy, typename... Ts>
+class MediaEventSourceImpl;
+
+/**
+ * Not thread-safe since this is not meant to be shared and therefore only
+ * move constructor is provided. Used to hold the result of
+ * MediaEventSource<T>::Connect() and call Disconnect() to disconnect the
+ * listener from an event source.
+ */
+class MediaEventListener {
+ template <ListenerPolicy, typename... Ts>
+ friend class MediaEventSourceImpl;
+
+ public:
+ MediaEventListener() = default;
+
+ MediaEventListener(MediaEventListener&& aOther)
+ : mToken(std::move(aOther.mToken)) {}
+
+ MediaEventListener& operator=(MediaEventListener&& aOther) {
+ MOZ_ASSERT(!mToken, "Must disconnect the listener.");
+ mToken = std::move(aOther.mToken);
+ return *this;
+ }
+
+ ~MediaEventListener() {
+ MOZ_ASSERT(!mToken, "Must disconnect the listener.");
+ }
+
+ void Disconnect() {
+ mToken->Revoke();
+ mToken = nullptr;
+ }
+
+ void DisconnectIfExists() {
+ if (mToken) {
+ Disconnect();
+ }
+ }
+
+ private:
+ // Avoid exposing RevocableToken directly to the client code so that
+ // listeners can be disconnected in a controlled manner.
+ explicit MediaEventListener(RevocableToken* aToken) : mToken(aToken) {}
+ RefPtr<RevocableToken> mToken;
+};
+
+/**
+ * A generic and thread-safe class to implement the observer pattern.
+ */
+template <ListenerPolicy Lp, typename... Es>
+class MediaEventSourceImpl {
+ static_assert(!detail::IsAnyReference<Es...>::value,
+ "Ref-type not supported!");
+
+ template <typename T>
+ using ArgType = typename detail::EventTypeTraits<T>::ArgType;
+
+ typedef detail::Listener<ArgType<Es>...> Listener;
+
+ template <typename Target, typename Func>
+ using ListenerImpl = detail::ListenerImpl<Target, Func, ArgType<Es>...>;
+
+ template <typename Method>
+ using TakeArgs = detail::TakeArgs<Method>;
+
+ void PruneListeners() {
+ mListeners.RemoveElementsBy(
+ [](const auto& listener) { return listener->IsRevoked(); });
+ }
+
+ template <typename Target, typename Function>
+ MediaEventListener ConnectInternal(Target* aTarget, Function&& aFunction) {
+ MutexAutoLock lock(mMutex);
+ PruneListeners();
+ MOZ_ASSERT(Lp == ListenerPolicy::NonExclusive || mListeners.IsEmpty());
+ auto l = mListeners.AppendElement();
+ *l = new ListenerImpl<Target, Function>(aTarget,
+ std::forward<Function>(aFunction));
+ return MediaEventListener(*l);
+ }
+
+ // |Method| takes one or more arguments.
+ template <typename Target, typename This, typename Method>
+ std::enable_if_t<TakeArgs<Method>::value, MediaEventListener> ConnectInternal(
+ Target* aTarget, This* aThis, Method aMethod) {
+ detail::RawPtr<This> thiz(aThis);
+ return ConnectInternal(aTarget, [=](ArgType<Es>&&... aEvents) {
+ (thiz.get()->*aMethod)(std::move(aEvents)...);
+ });
+ }
+
+ // |Method| takes no arguments. Don't bother passing the event data.
+ template <typename Target, typename This, typename Method>
+ std::enable_if_t<!TakeArgs<Method>::value, MediaEventListener>
+ ConnectInternal(Target* aTarget, This* aThis, Method aMethod) {
+ detail::RawPtr<This> thiz(aThis);
+ return ConnectInternal(aTarget, [=]() { (thiz.get()->*aMethod)(); });
+ }
+
+ public:
+ /**
+ * Register a function to receive notifications from the event source.
+ *
+ * @param aTarget The target thread on which the function will run.
+ * @param aFunction A function to be called on the target thread. The function
+ * parameter must be convertible from |EventType|.
+ * @return An object used to disconnect from the event source.
+ */
+ template <typename Function>
+ MediaEventListener Connect(AbstractThread* aTarget, Function&& aFunction) {
+ return ConnectInternal(aTarget, std::forward<Function>(aFunction));
+ }
+
+ template <typename Function>
+ MediaEventListener Connect(nsIEventTarget* aTarget, Function&& aFunction) {
+ return ConnectInternal(aTarget, std::forward<Function>(aFunction));
+ }
+
+ /**
+ * As above.
+ *
+ * Note we deliberately keep a weak reference to |aThis| in order not to
+ * change its lifetime. This is because notifications are dispatched
+ * asynchronously and removing a listener doesn't always break the reference
+ * cycle for the pending event could still hold a reference to |aThis|.
+ *
+ * The caller must call MediaEventListener::Disconnect() to avoid dangling
+ * pointers.
+ */
+ template <typename This, typename Method>
+ MediaEventListener Connect(AbstractThread* aTarget, This* aThis,
+ Method aMethod) {
+ return ConnectInternal(aTarget, aThis, aMethod);
+ }
+
+ template <typename This, typename Method>
+ MediaEventListener Connect(nsIEventTarget* aTarget, This* aThis,
+ Method aMethod) {
+ return ConnectInternal(aTarget, aThis, aMethod);
+ }
+
+ protected:
+ MediaEventSourceImpl() : mMutex("MediaEventSourceImpl::mMutex") {}
+
+ template <typename... Ts>
+ void NotifyInternal(Ts&&... aEvents) {
+ MutexAutoLock lock(mMutex);
+ int32_t last = static_cast<int32_t>(mListeners.Length()) - 1;
+ for (int32_t i = last; i >= 0; --i) {
+ auto&& l = mListeners[i];
+ // Remove disconnected listeners.
+ // It is not optimal but is simple and works well.
+ if (l->IsRevoked()) {
+ mListeners.RemoveElementAt(i);
+ continue;
+ }
+ l->Dispatch(std::forward<Ts>(aEvents)...);
+ }
+ }
+
+ private:
+ Mutex mMutex MOZ_UNANNOTATED;
+ nsTArray<RefPtr<Listener>> mListeners;
+};
+
+template <typename... Es>
+using MediaEventSource =
+ MediaEventSourceImpl<ListenerPolicy::NonExclusive, Es...>;
+
+template <typename... Es>
+using MediaEventSourceExc =
+ MediaEventSourceImpl<ListenerPolicy::Exclusive, Es...>;
+
+/**
+ * A class to separate the interface of event subject (MediaEventSource)
+ * and event publisher. Mostly used as a member variable to publish events
+ * to the listeners.
+ */
+template <typename... Es>
+class MediaEventProducer : public MediaEventSource<Es...> {
+ public:
+ template <typename... Ts>
+ void Notify(Ts&&... aEvents) {
+ // Pass lvalues to prevent move in NonExclusive mode.
+ this->NotifyInternal(aEvents...);
+ }
+};
+
+/**
+ * Specialization for void type. A dummy bool is passed to NotifyInternal
+ * since there is no way to pass a void value.
+ */
+template <>
+class MediaEventProducer<void> : public MediaEventSource<void> {
+ public:
+ void Notify() { this->NotifyInternal(true /* dummy */); }
+};
+
+/**
+ * A producer allowing at most one listener.
+ */
+template <typename... Es>
+class MediaEventProducerExc : public MediaEventSourceExc<Es...> {
+ public:
+ template <typename... Ts>
+ void Notify(Ts&&... aEvents) {
+ this->NotifyInternal(std::forward<Ts>(aEvents)...);
+ }
+};
+
+/**
+ * A class that facilitates forwarding MediaEvents from multiple sources of the
+ * same type into a single source.
+ *
+ * Lifetimes are convenient. A forwarded source is disconnected either by
+ * the source itself going away, or the forwarder being destroyed.
+ *
+ * Not threadsafe. The caller is responsible for calling Forward() in a
+ * threadsafe manner.
+ */
+template <typename... Es>
+class MediaEventForwarder : public MediaEventSource<Es...> {
+ public:
+ template <typename T>
+ using ArgType = typename detail::EventTypeTraits<T>::ArgType;
+
+ explicit MediaEventForwarder(nsCOMPtr<nsISerialEventTarget> aEventTarget)
+ : mEventTarget(std::move(aEventTarget)) {}
+
+ MediaEventForwarder(MediaEventForwarder&& aOther)
+ : mEventTarget(aOther.mEventTarget),
+ mListeners(std::move(aOther.mListeners)) {}
+
+ ~MediaEventForwarder() { MOZ_ASSERT(mListeners.IsEmpty()); }
+
+ MediaEventForwarder& operator=(MediaEventForwarder&& aOther) {
+ MOZ_RELEASE_ASSERT(mEventTarget == aOther.mEventTarget);
+ MOZ_ASSERT(mListeners.IsEmpty());
+ mListeners = std::move(aOther.mListeners);
+ }
+
+ void Forward(MediaEventSource<Es...>& aSource) {
+ // Forwarding a rawptr `this` here is fine, since DisconnectAll disconnect
+ // all mListeners synchronously and prevents this handler from running.
+ mListeners.AppendElement(
+ aSource.Connect(mEventTarget, [this](ArgType<Es>&&... aEvents) {
+ this->NotifyInternal(std::forward<ArgType<Es>...>(aEvents)...);
+ }));
+ }
+
+ template <typename Function>
+ void ForwardIf(MediaEventSource<Es...>& aSource, Function&& aFunction) {
+ // Forwarding a rawptr `this` here is fine, since DisconnectAll disconnect
+ // all mListeners synchronously and prevents this handler from running.
+ mListeners.AppendElement(aSource.Connect(
+ mEventTarget, [this, func = aFunction](ArgType<Es>&&... aEvents) {
+ if (!func()) {
+ return;
+ }
+ this->NotifyInternal(std::forward<ArgType<Es>...>(aEvents)...);
+ }));
+ }
+
+ void DisconnectAll() {
+ for (auto& l : mListeners) {
+ l.Disconnect();
+ }
+ mListeners.Clear();
+ }
+
+ private:
+ const nsCOMPtr<nsISerialEventTarget> mEventTarget;
+ nsTArray<MediaEventListener> mListeners;
+};
+
+} // namespace mozilla
+
+#endif // MediaEventSource_h_