/* -*- 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_AbstractEventQueue_h

#define mozilla_AbstractEventQueue_h

#include "mozilla/AlreadyAddRefed.h"

#include "mozilla/MemoryReporting.h"

#include "mozilla/Mutex.h"

class nsIRunnable;

namespace mozilla {

enum class EventPriority

{

  High,

  Input,

  Normal,

  Idle,

  Count

};

// AbstractEventQueue is an abstract base class for all our unsynchronized event

// queue implementations:

// - EventQueue: A queue of runnables. Used for non-main threads.

// - PrioritizedEventQueue: Contains a queue for each priority level.

//       Has heuristics to decide which queue to pop from. Events are

//       pushed into the queue corresponding to their priority.

//       Used for the main thread.

//

// Since AbstractEventQueue implementations are unsynchronized, they should be

// wrapped in an outer SynchronizedEventQueue implementation (like

// ThreadEventQueue).

//

// Subclasses should also define a `static const bool SupportsPrioritization`

// member to indicate whether the subclass cares about runnable priorities

// implemented through nsIRunnablePriority.

class AbstractEventQueue

{

public:

  // Add an event to the end of the queue. Implementors are free to use

  // aPriority however they wish.  If the runnable supports nsIRunnablePriority

  // and the implementing class supports prioritization, aPriority represents

  // the result of calling nsIRunnablePriority::GetPriority().

  virtual void PutEvent(already_AddRefed<nsIRunnable>&& aEvent,

                        EventPriority aPriority,

                        const MutexAutoLock& aProofOfLock) = 0;

  // Get an event from the front of the queue. aPriority is an out param. If the

  // implementation supports priorities, then this should be the same priority

  // that the event was pushed with. aPriority may be null. This should return

  // null if the queue is non-empty but the event in front is not ready to run.

  virtual already_AddRefed<nsIRunnable> GetEvent(EventPriority* aPriority,

                                                 const MutexAutoLock& aProofOfLock) = 0;

  // Returns true if the queue is empty. Implies !HasReadyEvent().

  virtual bool IsEmpty(const MutexAutoLock& aProofOfLock) = 0;

  // Returns true if the queue is non-empty and if the event in front is ready

  // to run. Implies !IsEmpty(). This should return true iff GetEvent returns a

  // non-null value.

  virtual bool HasReadyEvent(const MutexAutoLock& aProofOfLock) = 0;

  // Returns the number of events in the queue.

  virtual size_t Count(const MutexAutoLock& aProofOfLock) const = 0;

  virtual void EnableInputEventPrioritization(const MutexAutoLock& aProofOfLock) = 0;

  virtual void FlushInputEventPrioritization(const MutexAutoLock& aProofOfLock) = 0;

  virtual void SuspendInputEventPrioritization(const MutexAutoLock& aProofOfLock) = 0;

  virtual void ResumeInputEventPrioritization(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;

  virtual ~AbstractEventQueue() {}

};

} // namespace mozilla

#endif // mozilla_AbstractEventQueue_h