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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set sw=2 ts=8 et tw=80 :
+ */
+/* 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 mozilla_net_ChannelEventQueue_h
+#define mozilla_net_ChannelEventQueue_h
+
+#include "nsTArray.h"
+#include "nsIEventTarget.h"
+#include "nsThreadUtils.h"
+#include "nsXULAppAPI.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/Mutex.h"
+#include "mozilla/RecursiveMutex.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/Unused.h"
+
+class nsISupports;
+
+namespace mozilla {
+namespace net {
+
+class ChannelEvent {
+ public:
+ MOZ_COUNTED_DEFAULT_CTOR(ChannelEvent)
+ MOZ_COUNTED_DTOR_VIRTUAL(ChannelEvent) virtual void Run() = 0;
+ virtual already_AddRefed<nsIEventTarget> GetEventTarget() = 0;
+};
+
+// Note that MainThreadChannelEvent should not be used in child process since
+// GetEventTarget() directly returns an unlabeled event target.
+class MainThreadChannelEvent : public ChannelEvent {
+ public:
+ MOZ_COUNTED_DEFAULT_CTOR(MainThreadChannelEvent)
+ MOZ_COUNTED_DTOR_OVERRIDE(MainThreadChannelEvent)
+
+ already_AddRefed<nsIEventTarget> GetEventTarget() override {
+ MOZ_ASSERT(XRE_IsParentProcess());
+
+ return do_AddRef(GetMainThreadSerialEventTarget());
+ }
+};
+
+class ChannelFunctionEvent : public ChannelEvent {
+ public:
+ ChannelFunctionEvent(
+ std::function<already_AddRefed<nsIEventTarget>()>&& aGetEventTarget,
+ std::function<void()>&& aCallback)
+ : mGetEventTarget(std::move(aGetEventTarget)),
+ mCallback(std::move(aCallback)) {}
+
+ void Run() override { mCallback(); }
+ already_AddRefed<nsIEventTarget> GetEventTarget() override {
+ return mGetEventTarget();
+ }
+
+ private:
+ const std::function<already_AddRefed<nsIEventTarget>()> mGetEventTarget;
+ const std::function<void()> mCallback;
+};
+
+// UnsafePtr is a work-around our static analyzer that requires all
+// ref-counted objects to be captured in lambda via a RefPtr
+// The ChannelEventQueue makes it safe to capture "this" by pointer only.
+// This is required as work-around to prevent cycles until bug 1596295
+// is resolved.
+template <typename T>
+class UnsafePtr {
+ public:
+ explicit UnsafePtr(T* aPtr) : mPtr(aPtr) {}
+
+ T& operator*() const { return *mPtr; }
+ T* operator->() const {
+ MOZ_ASSERT(mPtr, "dereferencing a null pointer");
+ return mPtr;
+ }
+ operator T*() const& { return mPtr; }
+ explicit operator bool() const { return mPtr != nullptr; }
+
+ private:
+ T* const mPtr;
+};
+
+class NeckoTargetChannelFunctionEvent : public ChannelFunctionEvent {
+ public:
+ template <typename T>
+ NeckoTargetChannelFunctionEvent(T* aChild, std::function<void()>&& aCallback)
+ : ChannelFunctionEvent(
+ [child = UnsafePtr<T>(aChild)]() {
+ MOZ_ASSERT(child);
+ return child->GetNeckoTarget();
+ },
+ std::move(aCallback)) {}
+};
+
+// Workaround for Necko re-entrancy dangers. We buffer IPDL messages in a
+// queue if still dispatching previous one(s) to listeners/observers.
+// Otherwise synchronous XMLHttpRequests and/or other code that spins the
+// event loop (ex: IPDL rpc) could cause listener->OnDataAvailable (for
+// instance) to be dispatched and called before mListener->OnStartRequest has
+// completed.
+
+class ChannelEventQueue final {
+ NS_INLINE_DECL_THREADSAFE_REFCOUNTING(ChannelEventQueue)
+
+ public:
+ explicit ChannelEventQueue(nsISupports* owner)
+ : mSuspendCount(0),
+ mSuspended(false),
+ mForcedCount(0),
+ mFlushing(false),
+ mHasCheckedForXMLHttpRequest(false),
+ mForXMLHttpRequest(false),
+ mOwner(owner),
+ mMutex("ChannelEventQueue::mMutex"),
+ mRunningMutex("ChannelEventQueue::mRunningMutex") {}
+
+ // Puts IPDL-generated channel event into queue, to be run later
+ // automatically when EndForcedQueueing and/or Resume is called.
+ //
+ // @param aCallback - the ChannelEvent
+ // @param aAssertionWhenNotQueued - this optional param will be used in an
+ // assertion when the event is executed directly.
+ inline void RunOrEnqueue(ChannelEvent* aCallback,
+ bool aAssertionWhenNotQueued = false);
+
+ // Append ChannelEvent in front of the event queue.
+ inline void PrependEvent(UniquePtr<ChannelEvent>&& aEvent);
+ inline void PrependEvents(nsTArray<UniquePtr<ChannelEvent>>& aEvents);
+
+ // After StartForcedQueueing is called, RunOrEnqueue() will start enqueuing
+ // events that will be run/flushed when EndForcedQueueing is called.
+ // - Note: queueing may still be required after EndForcedQueueing() (if the
+ // queue is suspended, etc): always call RunOrEnqueue() to avoid race
+ // conditions.
+ inline void StartForcedQueueing();
+ inline void EndForcedQueueing();
+
+ // Suspend/resume event queue. RunOrEnqueue() will start enqueuing
+ // events and they will be run/flushed when resume is called. These should be
+ // called when the channel owning the event queue is suspended/resumed.
+ void Suspend();
+ // Resume flushes the queue asynchronously, i.e. items in queue will be
+ // dispatched in a new event on the current thread.
+ void Resume();
+
+ void NotifyReleasingOwner() {
+ MutexAutoLock lock(mMutex);
+ mOwner = nullptr;
+ }
+
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+ bool IsEmpty() {
+ MutexAutoLock lock(mMutex);
+ return mEventQueue.IsEmpty();
+ }
+#endif
+
+ private:
+ // Private destructor, to discourage deletion outside of Release():
+ ~ChannelEventQueue() = default;
+
+ void SuspendInternal();
+ void ResumeInternal();
+
+ bool MaybeSuspendIfEventsAreSuppressed() MOZ_REQUIRES(mMutex);
+
+ inline void MaybeFlushQueue();
+ void FlushQueue();
+ inline void CompleteResume();
+
+ ChannelEvent* TakeEvent();
+
+ nsTArray<UniquePtr<ChannelEvent>> mEventQueue MOZ_GUARDED_BY(mMutex);
+
+ uint32_t mSuspendCount MOZ_GUARDED_BY(mMutex);
+ bool mSuspended MOZ_GUARDED_BY(mMutex);
+ uint32_t mForcedCount // Support ForcedQueueing on multiple thread.
+ MOZ_GUARDED_BY(mMutex);
+ bool mFlushing MOZ_GUARDED_BY(mMutex);
+
+ // Whether the queue is associated with an XHR. This is lazily instantiated
+ // the first time it is needed. These are MainThread-only.
+ bool mHasCheckedForXMLHttpRequest;
+ bool mForXMLHttpRequest;
+
+ // Keep ptr to avoid refcount cycle: only grab ref during flushing.
+ nsISupports* mOwner MOZ_GUARDED_BY(mMutex);
+
+ // For atomic mEventQueue operation and state update
+ Mutex mMutex;
+
+ // To guarantee event execution order among threads
+ RecursiveMutex mRunningMutex MOZ_ACQUIRED_BEFORE(mMutex);
+
+ friend class AutoEventEnqueuer;
+};
+
+inline void ChannelEventQueue::RunOrEnqueue(ChannelEvent* aCallback,
+ bool aAssertionWhenNotQueued) {
+ MOZ_ASSERT(aCallback);
+ // Events execution could be a destruction of the channel (and our own
+ // destructor) unless we make sure its refcount doesn't drop to 0 while this
+ // method is running.
+ nsCOMPtr<nsISupports> kungFuDeathGrip;
+
+ // To avoid leaks.
+ UniquePtr<ChannelEvent> event(aCallback);
+
+ // To guarantee that the running event and all the events generated within
+ // it will be finished before events on other threads.
+ RecursiveMutexAutoLock lock(mRunningMutex);
+ {
+ MutexAutoLock lock(mMutex);
+ kungFuDeathGrip = mOwner; // must be under the lock
+
+ bool enqueue = !!mForcedCount || mSuspended || mFlushing ||
+ !mEventQueue.IsEmpty() ||
+ MaybeSuspendIfEventsAreSuppressed();
+
+ if (enqueue) {
+ mEventQueue.AppendElement(std::move(event));
+ return;
+ }
+
+ nsCOMPtr<nsIEventTarget> target = event->GetEventTarget();
+ MOZ_ASSERT(target);
+
+ bool isCurrentThread = false;
+ DebugOnly<nsresult> rv = target->IsOnCurrentThread(&isCurrentThread);
+ MOZ_ASSERT(NS_SUCCEEDED(rv));
+
+ if (!isCurrentThread) {
+ // Leverage Suspend/Resume mechanism to trigger flush procedure without
+ // creating a new one.
+ SuspendInternal();
+ mEventQueue.AppendElement(std::move(event));
+ ResumeInternal();
+ return;
+ }
+ }
+
+ MOZ_RELEASE_ASSERT(!aAssertionWhenNotQueued);
+ event->Run();
+}
+
+inline void ChannelEventQueue::StartForcedQueueing() {
+ MutexAutoLock lock(mMutex);
+ ++mForcedCount;
+}
+
+inline void ChannelEventQueue::EndForcedQueueing() {
+ bool tryFlush = false;
+ {
+ MutexAutoLock lock(mMutex);
+ MOZ_ASSERT(mForcedCount > 0);
+ if (!--mForcedCount) {
+ tryFlush = true;
+ }
+ }
+
+ if (tryFlush) {
+ MaybeFlushQueue();
+ }
+}
+
+inline void ChannelEventQueue::PrependEvent(UniquePtr<ChannelEvent>&& aEvent) {
+ MutexAutoLock lock(mMutex);
+
+ // Prepending event while no queue flush foreseen might cause the following
+ // channel events not run. This assertion here guarantee there must be a
+ // queue flush, either triggered by Resume or EndForcedQueueing, to execute
+ // the added event.
+ MOZ_ASSERT(mSuspended || !!mForcedCount);
+
+ mEventQueue.InsertElementAt(0, std::move(aEvent));
+}
+
+inline void ChannelEventQueue::PrependEvents(
+ nsTArray<UniquePtr<ChannelEvent>>& aEvents) {
+ MutexAutoLock lock(mMutex);
+
+ // Prepending event while no queue flush foreseen might cause the following
+ // channel events not run. This assertion here guarantee there must be a
+ // queue flush, either triggered by Resume or EndForcedQueueing, to execute
+ // the added events.
+ MOZ_ASSERT(mSuspended || !!mForcedCount);
+
+ mEventQueue.InsertElementsAt(0, aEvents.Length());
+
+ for (uint32_t i = 0; i < aEvents.Length(); i++) {
+ mEventQueue[i] = std::move(aEvents[i]);
+ }
+}
+
+inline void ChannelEventQueue::CompleteResume() {
+ bool tryFlush = false;
+ {
+ MutexAutoLock lock(mMutex);
+
+ // channel may have been suspended again since Resume fired event to call
+ // this.
+ if (!mSuspendCount) {
+ // we need to remain logically suspended (for purposes of queuing incoming
+ // messages) until this point, else new incoming messages could run before
+ // queued ones.
+ mSuspended = false;
+ tryFlush = true;
+ }
+ }
+
+ if (tryFlush) {
+ MaybeFlushQueue();
+ }
+}
+
+inline void ChannelEventQueue::MaybeFlushQueue() {
+ // Don't flush if forced queuing on, we're already being flushed, or
+ // suspended, or there's nothing to flush
+ bool flushQueue = false;
+
+ {
+ MutexAutoLock lock(mMutex);
+ flushQueue = !mForcedCount && !mFlushing && !mSuspended &&
+ !mEventQueue.IsEmpty() && !MaybeSuspendIfEventsAreSuppressed();
+
+ // Only one thread is allowed to run FlushQueue at a time.
+ if (flushQueue) {
+ mFlushing = true;
+ }
+ }
+
+ if (flushQueue) {
+ FlushQueue();
+ }
+}
+
+// Ensures that RunOrEnqueue() will be collecting events during its lifetime
+// (letting caller know incoming IPDL msgs should be queued). Flushes the queue
+// when it goes out of scope.
+class MOZ_STACK_CLASS AutoEventEnqueuer {
+ public:
+ explicit AutoEventEnqueuer(ChannelEventQueue* queue) : mEventQueue(queue) {
+ {
+ // Probably not actually needed, since NotifyReleasingOwner should
+ // only happen after this, but safer to take it in case things change
+ MutexAutoLock lock(queue->mMutex);
+ mOwner = queue->mOwner;
+ }
+ mEventQueue->StartForcedQueueing();
+ }
+ ~AutoEventEnqueuer() { mEventQueue->EndForcedQueueing(); }
+
+ private:
+ RefPtr<ChannelEventQueue> mEventQueue;
+ // Ensure channel object lives longer than ChannelEventQueue.
+ nsCOMPtr<nsISupports> mOwner;
+};
+
+} // namespace net
+} // namespace mozilla
+
+#endif