1 files changed, 618 insertions, 0 deletions
diff --git a/dom/media/MediaEventSource.h b/dom/media/MediaEventSource.h
new file mode 100644
index 000000000..eb0451e49
--- /dev/null
+++ b/dom/media/MediaEventSource.h
@@ -0,0 +1,618 @@
+/* -*- 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 "mozilla/AbstractThread.h"
+#include "mozilla/Atomics.h"
+#include "mozilla/IndexSequence.h"
+#include "mozilla/Mutex.h"
+#include "mozilla/Tuple.h"
+#include "mozilla/TypeTraits.h"
+#include "mozilla/UniquePtr.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() : mRevoked(false) {}
+
+  void Revoke() {
+    mRevoked = true;
+  }
+
+  bool IsRevoked() const {
+    return mRevoked;
+  }
+
+private:
+  ~RevocableToken() {}
+  Atomic<bool> mRevoked;
+};
+
+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
+};
+
+enum class DispatchPolicy : int8_t {
+  Sync, // Events are passed synchronously to the listeners.
+  Async // Events are passed asynchronously to the listeners.
+};
+
+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 FalseType test(void(C::*)(), int);
+  template <typename C> static FalseType test(void(C::*)() const, int);
+  template <typename C> static FalseType test(void(C::*)() volatile, int);
+  template <typename C> static FalseType test(void(C::*)() const volatile, int);
+  template <typename F> static FalseType test(F&&, decltype(DeclVal<F>()(), 0));
+  static TrueType test(...);
+public:
+  typedef decltype(test(DeclVal<T>(), 0)) Type;
+};
+
+template <typename T>
+struct TakeArgs : public TakeArgsHelper<T>::Type {};
+
+template <DispatchPolicy Dp, typename T> struct EventTarget;
+
+template <>
+struct EventTarget<DispatchPolicy::Async, nsIEventTarget> {
+  static void
+  Dispatch(nsIEventTarget* aTarget, already_AddRefed<nsIRunnable> aTask) {
+    aTarget->Dispatch(Move(aTask), NS_DISPATCH_NORMAL);
+  }
+};
+
+template <>
+struct EventTarget<DispatchPolicy::Async, AbstractThread> {
+  static void
+  Dispatch(AbstractThread* aTarget, already_AddRefed<nsIRunnable> aTask) {
+    aTarget->Dispatch(Move(aTask), AbstractThread::DontAssertDispatchSuccess);
+  }
+};
+
+template <>
+struct EventTarget<DispatchPolicy::Sync, nsIEventTarget> {
+  static bool IsOnCurrentThread(nsIEventTarget* aTarget) {
+    bool current = false;
+    auto rv = aTarget->IsOnCurrentThread(&current);
+    return NS_SUCCEEDED(rv) && current;
+  }
+  static void
+  Dispatch(nsIEventTarget* aTarget, already_AddRefed<nsIRunnable> aTask) {
+    MOZ_ASSERT(IsOnCurrentThread(aTarget));
+    nsCOMPtr<nsIRunnable> r = aTask;
+    r->Run();
+  }
+};
+
+template <>
+struct EventTarget<DispatchPolicy::Sync, AbstractThread> {
+  static void
+  Dispatch(AbstractThread* aTarget, already_AddRefed<nsIRunnable> aTask) {
+    MOZ_ASSERT(aTarget->IsCurrentThreadIn());
+    nsCOMPtr<nsIRunnable> r = aTask;
+    r->Run();
+  }
+};
+
+/**
+ * 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;
+};
+
+/**
+ * A helper class to pass event data to the listeners. Optimized to save
+ * copy when Move is possible or |Function| takes no arguments.
+ */
+template<DispatchPolicy Dp, typename Target, typename Function>
+class ListenerHelper {
+  // Define our custom runnable to minimize copy of the event data.
+  // NS_NewRunnableFunction will result in 2 copies of the event data.
+  // One is captured by the lambda and the other is the copy of the lambda.
+  template <typename... Ts>
+  class R : public Runnable {
+  public:
+    template <typename... Us>
+    R(RevocableToken* aToken, const Function& aFunction, Us&&... aEvents)
+      : mToken(aToken)
+      , mFunction(aFunction)
+      , mEvents(Forward<Us>(aEvents)...) {}
+
+    template <typename... Vs, size_t... Is>
+    void Invoke(Tuple<Vs...>& aEvents, IndexSequence<Is...>) {
+      // Enable move whenever possible since mEvent won't be used anymore.
+      mFunction(Move(Get<Is>(aEvents))...);
+    }
+
+    NS_IMETHOD Run() override {
+      // Don't call the listener if it is disconnected.
+      if (!mToken->IsRevoked()) {
+        Invoke(mEvents, typename IndexSequenceFor<Ts...>::Type());
+      }
+      return NS_OK;
+    }
+
+  private:
+    RefPtr<RevocableToken> mToken;
+    Function mFunction;
+
+    template <typename T>
+    using ArgType = typename RemoveCV<typename RemoveReference<T>::Type>::Type;
+    Tuple<ArgType<Ts>...> mEvents;
+  };
+
+public:
+  ListenerHelper(RevocableToken* aToken, Target* aTarget, const Function& aFunc)
+    : mToken(aToken), mTarget(aTarget), mFunction(aFunc) {}
+
+  // |F| takes one or more arguments.
+  template <typename F, typename... Ts>
+  typename EnableIf<TakeArgs<F>::value, void>::Type
+  DispatchHelper(const F& aFunc, Ts&&... aEvents) {
+    nsCOMPtr<nsIRunnable> r =
+      new R<Ts...>(mToken, aFunc, Forward<Ts>(aEvents)...);
+    EventTarget<Dp, Target>::Dispatch(mTarget.get(), r.forget());
+  }
+
+  // |F| takes no arguments. Don't bother passing aEvent.
+  template <typename F, typename... Ts>
+  typename EnableIf<!TakeArgs<F>::value, void>::Type
+  DispatchHelper(const F& aFunc, Ts&&...) {
+    const RefPtr<RevocableToken>& token = mToken;
+    nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction([=] () {
+      // Don't call the listener if it is disconnected.
+      if (!token->IsRevoked()) {
+        aFunc();
+      }
+    });
+    EventTarget<Dp, Target>::Dispatch(mTarget.get(), r.forget());
+  }
+
+  template <typename... Ts>
+  void Dispatch(Ts&&... aEvents) {
+    DispatchHelper(mFunction, Forward<Ts>(aEvents)...);
+  }
+
+private:
+  RefPtr<RevocableToken> mToken;
+  const RefPtr<Target> mTarget;
+  Function mFunction;
+};
+
+/**
+ * Define whether an event data should be copied or moved to the listeners.
+ *
+ * @Copy Data will always be copied. Each listener gets a copy.
+ * @Move Data will always be moved.
+ */
+enum class EventPassMode : int8_t {
+  Copy,
+  Move
+};
+
+class ListenerBase {
+public:
+  ListenerBase() : mToken(new RevocableToken()) {}
+  ~ListenerBase() {
+    MOZ_ASSERT(Token()->IsRevoked(), "Must disconnect the listener.");
+  }
+  RevocableToken* Token() const {
+    return mToken;
+  }
+private:
+  const RefPtr<RevocableToken> mToken;
+};
+
+/**
+ * Stored by MediaEventSource to send notifications to the listener.
+ * Since virtual methods can not be templated, this class is specialized
+ * to provide different Dispatch() overloads depending on EventPassMode.
+ */
+template <EventPassMode Mode, typename... As>
+class Listener : public ListenerBase {
+public:
+  virtual ~Listener() {}
+  virtual void Dispatch(const As&... aEvents) = 0;
+};
+
+template <typename... As>
+class Listener<EventPassMode::Move, As...> : public ListenerBase {
+public:
+  virtual ~Listener() {}
+  virtual void Dispatch(As... aEvents) = 0;
+};
+
+/**
+ * Store the registered target thread and function so it knows where and to
+ * whom to send the event data.
+ */
+template <DispatchPolicy Dp, typename Target,
+          typename Function, EventPassMode, typename... As>
+class ListenerImpl : public Listener<EventPassMode::Copy, As...> {
+public:
+  ListenerImpl(Target* aTarget, const Function& aFunction)
+    : mHelper(ListenerBase::Token(), aTarget, aFunction) {}
+  void Dispatch(const As&... aEvents) override {
+    mHelper.Dispatch(aEvents...);
+  }
+private:
+  ListenerHelper<Dp, Target, Function> mHelper;
+};
+
+template <DispatchPolicy Dp, typename Target, typename Function, typename... As>
+class ListenerImpl<Dp, Target, Function, EventPassMode::Move, As...>
+  : public Listener<EventPassMode::Move, As...> {
+public:
+  ListenerImpl(Target* aTarget, const Function& aFunction)
+    : mHelper(ListenerBase::Token(), aTarget, aFunction) {}
+  void Dispatch(As... aEvents) override {
+    mHelper.Dispatch(Move(aEvents)...);
+  }
+private:
+  ListenerHelper<Dp, Target, Function> mHelper;
+};
+
+/**
+ * Select EventPassMode based on ListenerPolicy.
+ *
+ * @Copy Selected when ListenerPolicy is NonExclusive because each listener
+ * must get a copy.
+ *
+ * @Move Selected when ListenerPolicy is Exclusive. All types passed to
+ * MediaEventProducer::Notify() must be movable.
+ */
+template <ListenerPolicy Lp>
+struct PassModePicker {
+  static const EventPassMode Value =
+    Lp == ListenerPolicy::NonExclusive ?
+    EventPassMode::Copy : EventPassMode::Move;
+};
+
+/**
+ * Return true if any type is a reference type.
+ */
+template <typename Head, typename... Tails>
+struct IsAnyReference {
+  static const bool value = IsReference<Head>::value ||
+                            IsAnyReference<Tails...>::value;
+};
+
+template <typename T>
+struct IsAnyReference<T> {
+  static const bool value = IsReference<T>::value;
+};
+
+} // namespace detail
+
+template <DispatchPolicy, 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 <DispatchPolicy, ListenerPolicy, typename... Ts>
+  friend class MediaEventSourceImpl;
+
+public:
+  MediaEventListener() {}
+
+  MediaEventListener(MediaEventListener&& aOther)
+    : mToken(Move(aOther.mToken)) {}
+
+  MediaEventListener& operator=(MediaEventListener&& aOther) {
+    MOZ_ASSERT(!mToken, "Must disconnect the listener.");
+    mToken = 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 <DispatchPolicy Dp, 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;
+
+  static const detail::EventPassMode PassMode =
+    detail::PassModePicker<Lp>::Value;
+
+  typedef detail::Listener<PassMode, ArgType<Es>...> Listener;
+
+  template<typename Target, typename Func>
+  using ListenerImpl =
+    detail::ListenerImpl<Dp, Target, Func, PassMode, ArgType<Es>...>;
+
+  template <typename Method>
+  using TakeArgs = detail::TakeArgs<Method>;
+
+  void PruneListeners() {
+    int32_t last = static_cast<int32_t>(mListeners.Length()) - 1;
+    for (int32_t i = last; i >= 0; --i) {
+      if (mListeners[i]->Token()->IsRevoked()) {
+        mListeners.RemoveElementAt(i);
+      }
+    }
+  }
+
+  template<typename Target, typename Function>
+  MediaEventListener
+  ConnectInternal(Target* aTarget, const Function& aFunction) {
+    MutexAutoLock lock(mMutex);
+    PruneListeners();
+    MOZ_ASSERT(Lp == ListenerPolicy::NonExclusive || mListeners.IsEmpty());
+    auto l = mListeners.AppendElement();
+    l->reset(new ListenerImpl<Target, Function>(aTarget, aFunction));
+    return MediaEventListener((*l)->Token());
+  }
+
+  // |Method| takes one or more arguments.
+  template <typename Target, typename This, typename Method>
+  typename EnableIf<TakeArgs<Method>::value, MediaEventListener>::Type
+  ConnectInternal(Target* aTarget, This* aThis, Method aMethod) {
+    detail::RawPtr<This> thiz(aThis);
+    auto f = [=] (ArgType<Es>&&... aEvents) {
+      (thiz.get()->*aMethod)(Move(aEvents)...);
+    };
+    return ConnectInternal(aTarget, f);
+  }
+
+  // |Method| takes no arguments. Don't bother passing the event data.
+  template <typename Target, typename This, typename Method>
+  typename EnableIf<!TakeArgs<Method>::value, MediaEventListener>::Type
+  ConnectInternal(Target* aTarget, This* aThis, Method aMethod) {
+    detail::RawPtr<This> thiz(aThis);
+    auto f = [=] () {
+      (thiz.get()->*aMethod)();
+    };
+    return ConnectInternal(aTarget, f);
+  }
+
+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, const Function& aFunction) {
+    return ConnectInternal(aTarget, aFunction);
+  }
+
+  template<typename Function>
+  MediaEventListener
+  Connect(nsIEventTarget* aTarget, const Function& aFunction) {
+    return ConnectInternal(aTarget, 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 <DispatchPolicy P, typename... Ts>
+  typename EnableIf<P == DispatchPolicy::Async, void>::Type
+  NotifyInternal(IntegralConstant<DispatchPolicy, P>, 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->Token()->IsRevoked()) {
+        mListeners.RemoveElementAt(i);
+        continue;
+      }
+      l->Dispatch(Forward<Ts>(aEvents)...);
+    }
+  }
+
+  template <DispatchPolicy P, typename... Ts>
+  typename EnableIf<P == DispatchPolicy::Sync, void>::Type
+  NotifyInternal(IntegralConstant<DispatchPolicy, P>, Ts&&... aEvents) {
+    // Move |mListeners| to a new container before iteration to prevent
+    // |mListeners| from being disrupted if the listener calls Connect() to
+    // modify |mListeners| in the callback function.
+    nsTArray<UniquePtr<Listener>> listeners;
+    listeners.SwapElements(mListeners);
+    for (auto&& l : listeners) {
+      l->Dispatch(Forward<Ts>(aEvents)...);
+    }
+    PruneListeners();
+    // Move remaining listeners back to |mListeners|.
+    for (auto&& l : listeners) {
+      if (!l->Token()->IsRevoked()) {
+        mListeners.AppendElement(Move(l));
+      }
+    }
+    // Perform sanity checks.
+    MOZ_ASSERT(Lp == ListenerPolicy::NonExclusive || mListeners.Length() <= 1);
+  }
+
+  template <typename... Ts>
+  void Notify(Ts&&... aEvents) {
+    NotifyInternal(IntegralConstant<DispatchPolicy, Dp>(),
+                   Forward<Ts>(aEvents)...);
+  }
+
+private:
+  Mutex mMutex;
+  nsTArray<UniquePtr<Listener>> mListeners;
+};
+
+template <typename... Es>
+using MediaEventSource =
+  MediaEventSourceImpl<DispatchPolicy::Async,
+                       ListenerPolicy::NonExclusive, Es...>;
+
+template <typename... Es>
+using MediaEventSourceExc =
+  MediaEventSourceImpl<DispatchPolicy::Async, 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:
+  using MediaEventSource<Es...>::Notify;
+};
+
+/**
+ * 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() {
+    MediaEventSource<void>::Notify(false /* dummy */);
+  }
+};
+
+/**
+ * A producer allowing at most one listener.
+ */
+template <typename... Es>
+class MediaEventProducerExc : public MediaEventSourceExc<Es...> {
+public:
+  using MediaEventSourceExc<Es...>::Notify;
+};
+
+/**
+ * Events are passed directly to the callback function of the listeners without
+ * dispatching. Note this class is not thread-safe. Both Connect() and Notify()
+ * must be called on the same thread.
+ */
+template <typename... Es>
+class MediaCallback
+  : public MediaEventSourceImpl<DispatchPolicy::Sync,
+                                ListenerPolicy::NonExclusive, Es...> {
+public:
+  using MediaEventSourceImpl<DispatchPolicy::Sync,
+                             ListenerPolicy::NonExclusive, Es...>::Notify;
+};
+
+/**
+ * A special version of MediaCallback which allows at most one listener.
+ */
+template <typename... Es>
+class MediaCallbackExc
+  : public MediaEventSourceImpl<DispatchPolicy::Sync,
+                                ListenerPolicy::Exclusive, Es...> {
+public:
+  using MediaEventSourceImpl<DispatchPolicy::Sync,
+                             ListenerPolicy::Exclusive, Es...>::Notify;
+};
+
+} // namespace mozilla
+
+#endif //MediaEventSource_h_