/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

/* 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/. */

/**

 * DecodePool manages the threads used for decoding raster images.

 */

#ifndef mozilla_image_DecodePool_h

#define mozilla_image_DecodePool_h

#include "mozilla/Mutex.h"

#include "mozilla/StaticPtr.h"

#include "nsCOMArray.h"

#include "nsCOMPtr.h"

#include "nsIEventTarget.h"

#include "nsIObserver.h"

#include "mozilla/RefPtr.h"

#include "nsStringFwd.h"

class nsIThread;

class nsIThreadPool;

namespace mozilla {

namespace image {

class Decoder;

class DecodePoolImpl;

class IDecodingTask;

/**

 * DecodePool is a singleton class that manages decoding of raster images. It

 * owns a pool of image decoding threads that are used for asynchronous

 * decoding.

 *

 * DecodePool allows callers to run a decoder, handling management of the

 * decoder's lifecycle and whether it executes on the main thread,

 * off-main-thread in the image decoding thread pool, or on some combination of

 * the two.

 */

class DecodePool final : public nsIObserver {

 public:

  NS_DECL_THREADSAFE_ISUPPORTS

  NS_DECL_NSIOBSERVER

  /// Initializes the singleton instance. Should be called from the main thread.

  static void Initialize();

  /// Returns the singleton instance.

  static DecodePool* Singleton();

  /// @return the number of processor cores we have available. This is not the

  /// same as the number of decoding threads we're actually using.

  static uint32_t NumberOfCores();

  /// True if the DecodePool is being shutdown. This may only be called by

  /// threads from the pool to check if they should keep working or not.

  bool IsShuttingDown() const;

  /// Ask the DecodePool to run @aTask asynchronously and return immediately.

  void AsyncRun(IDecodingTask* aTask);

  /**

   * Run @aTask synchronously if the task would prefer it. It's up to the task

   * itself to make this decision; @see IDecodingTask::ShouldPreferSyncRun(). If

   * @aTask doesn't prefer it, just run @aTask asynchronously and return

   * immediately.

   * @return true if the task was run sync, false otherwise.

   */

  bool SyncRunIfPreferred(IDecodingTask* aTask, const nsCString& aURI);

  /**

   * Run @aTask synchronously. This does not guarantee that @aTask will complete

   * synchronously. If, for example, @aTask doesn't yet have the data it needs

   * to run synchronously, it may recover by scheduling an async task to finish

   * up the work when the remaining data is available.

   */

  void SyncRunIfPossible(IDecodingTask* aTask, const nsCString& aURI);

  /**

   * Returns an event target interface to the DecodePool's I/O thread. Callers

   * who want to deliver data to workers on the DecodePool can use this event

   * target.

   *

   * @return An nsIEventTarget interface to the thread pool's I/O thread.

   */

  already_AddRefed<nsIEventTarget> GetIOEventTarget();

 private:

  friend class DecodePoolWorker;

  DecodePool();

  virtual ~DecodePool();

  static StaticRefPtr<DecodePool> sSingleton;

  static uint32_t sNumCores;

  RefPtr<DecodePoolImpl> mImpl;

  // mMutex protects mIOThread.

  Mutex mMutex;

  nsCOMPtr<nsIThread> mIOThread;

};

}  // namespace image

}  // namespace mozilla

#endif  // mozilla_image_DecodePool_h