1 files changed, 119 insertions, 0 deletions
diff --git a/xpcom/threads/SynchronizedEventQueue.h b/xpcom/threads/SynchronizedEventQueue.h
new file mode 100644
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+++ b/xpcom/threads/SynchronizedEventQueue.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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_SynchronizedEventQueue_h
+#define mozilla_SynchronizedEventQueue_h
+
+#include "mozilla/AlreadyAddRefed.h"
+#include "mozilla/EventQueue.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/Mutex.h"
+#include "nsIThreadInternal.h"
+#include "nsCOMPtr.h"
+#include "nsTObserverArray.h"
+
+class nsIEventTarget;
+class nsISerialEventTarget;
+class nsIThreadObserver;
+
+namespace mozilla {
+
+// A SynchronizedEventQueue is an abstract class for event queues that can be
+// used across threads. A SynchronizedEventQueue implementation will typically
+// use locks and condition variables to guarantee consistency. The methods of
+// SynchronizedEventQueue are split between ThreadTargetSink (which contains
+// methods for posting events) and SynchronizedEventQueue (which contains
+// methods for getting events). This split allows event targets (specifically
+// ThreadEventTarget) to use a narrow interface, since they only need to post
+// events.
+//
+// ThreadEventQueue is the canonical implementation of
+// SynchronizedEventQueue. When Quantum DOM is implemented, we will use a
+// different synchronized queue on the main thread, SchedulerEventQueue, which
+// will handle the cooperative threading model.
+
+class ThreadTargetSink {
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(ThreadTargetSink)
+
+  virtual bool PutEvent(already_AddRefed<nsIRunnable>&& aEvent,
+                        EventQueuePriority aPriority) = 0;
+
+  // After this method is called, no more events can be posted.
+  virtual void Disconnect(const MutexAutoLock& aProofOfLock) = 0;
+
+  size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const {
+    return aMallocSizeOf(this) + SizeOfExcludingThis(aMallocSizeOf);
+  }
+
+  virtual size_t SizeOfExcludingThis(
+      mozilla::MallocSizeOf aMallocSizeOf) const = 0;
+
+ protected:
+  virtual ~ThreadTargetSink() = default;
+};
+
+class SynchronizedEventQueue : public ThreadTargetSink {
+ public:
+  virtual already_AddRefed<nsIRunnable> GetEvent(
+      bool aMayWait, mozilla::TimeDuration* aLastEventDelay = nullptr) = 0;
+  virtual bool HasPendingEvent() = 0;
+
+  // This method atomically checks if there are pending events and, if there are
+  // none, forbids future events from being posted. It returns true if there
+  // were no pending events.
+  virtual bool ShutdownIfNoPendingEvents() = 0;
+
+  // These methods provide access to an nsIThreadObserver, whose methods are
+  // called when posting and processing events. SetObserver should only be
+  // called on the thread that processes events. GetObserver can be called from
+  // any thread. GetObserverOnThread must be used from the thread that processes
+  // events; it does not acquire a lock.
+  virtual already_AddRefed<nsIThreadObserver> GetObserver() = 0;
+  virtual already_AddRefed<nsIThreadObserver> GetObserverOnThread() = 0;
+  virtual void SetObserver(nsIThreadObserver* aObserver) = 0;
+
+  void AddObserver(nsIThreadObserver* aObserver);
+  void RemoveObserver(nsIThreadObserver* aObserver);
+  const nsTObserverArray<nsCOMPtr<nsIThreadObserver>>& EventObservers();
+
+  size_t SizeOfExcludingThis(
+      mozilla::MallocSizeOf aMallocSizeOf) const override {
+    return mEventObservers.ShallowSizeOfExcludingThis(aMallocSizeOf);
+  }
+
+  /**
+   * This method causes any events currently enqueued on the thread to be
+   * suppressed until PopEventQueue is called, and any event dispatched to this
+   * thread's nsIEventTarget will queue as well. Calls to PushEventQueue may be
+   * nested and must each be paired with a call to PopEventQueue in order to
+   * restore the original state of the thread. The returned nsIEventTarget may
+   * be used to push events onto the nested queue. Dispatching will be disabled
+   * once the event queue is popped. The thread will only ever process pending
+   * events for the innermost event queue. Must only be called on the target
+   * thread.
+   */
+  virtual already_AddRefed<nsISerialEventTarget> PushEventQueue() = 0;
+
+  /**
+   * Revert a call to PushEventQueue. When an event queue is popped, any events
+   * remaining in the queue are appended to the elder queue. This also causes
+   * the nsIEventTarget returned from PushEventQueue to stop dispatching events.
+   * Must only be called on the target thread, and with the innermost event
+   * queue.
+   */
+  virtual void PopEventQueue(nsIEventTarget* aTarget) = 0;
+
+ protected:
+  virtual ~SynchronizedEventQueue() = default;
+
+ private:
+  nsTObserverArray<nsCOMPtr<nsIThreadObserver>> mEventObservers;
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_SynchronizedEventQueue_h