gecko/dom/media/MediaManager.cpp

/* 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/. */

#include "MediaManager.h"

#include "MediaStreamGraph.h"
#include "nsIDOMFile.h"
#include "nsIEventTarget.h"
#include "nsIScriptGlobalObject.h"
#include "nsIPopupWindowManager.h"

#include "nsJSUtils.h"
#include "nsDOMFile.h"
#include "nsGlobalWindow.h"

/* Using WebRTC backend on Desktops (Mac, Windows, Linux), otherwise default */
#include "MediaEngineDefault.h"
#if defined(MOZ_WEBRTC)
#include "MediaEngineWebRTC.h"
#endif

namespace mozilla {

/**
 * Send an error back to content. The error is the form a string.
 * Do this only on the main thread. The success callback is also passed here
 * so it can be released correctly.
 */
class ErrorCallbackRunnable : public nsRunnable
{
public:
  ErrorCallbackRunnable(
    already_AddRefed<nsIDOMGetUserMediaSuccessCallback> aSuccess,
    already_AddRefed<nsIDOMGetUserMediaErrorCallback> aError,
    const nsString& aErrorMsg, uint64_t aWindowID)
    : mSuccess(aSuccess)
    , mError(aError)
    , mErrorMsg(aErrorMsg)
    , mWindowID(aWindowID) {}

  NS_IMETHOD
  Run()
  {
    // Only run if the window is still active.
    NS_ASSERTION(NS_IsMainThread(), "Only call on main thread");

    nsCOMPtr<nsIDOMGetUserMediaSuccessCallback> success(mSuccess);
    nsCOMPtr<nsIDOMGetUserMediaErrorCallback> error(mError);

    WindowTable* activeWindows = MediaManager::Get()->GetActiveWindows();
    if (activeWindows->Get(mWindowID)) {
      error->OnError(mErrorMsg);
    }
    return NS_OK;
  }

private:
  already_AddRefed<nsIDOMGetUserMediaSuccessCallback> mSuccess;
  already_AddRefed<nsIDOMGetUserMediaErrorCallback> mError;
  const nsString mErrorMsg;
  uint64_t mWindowID;
};

/**
 * Invoke the "onSuccess" callback in content. The callback will take a
 * DOMBlob in the case of {picture:true}, and a MediaStream in the case of
 * {audio:true} or {video:true}. There is a constructor available for each
 * form. Do this only on the main thread.
 */
class SuccessCallbackRunnable : public nsRunnable
{
public:
  SuccessCallbackRunnable(
    already_AddRefed<nsIDOMGetUserMediaSuccessCallback> aSuccess,
    already_AddRefed<nsIDOMGetUserMediaErrorCallback> aError,
    nsIDOMFile* aFile, uint64_t aWindowID)
    : mSuccess(aSuccess)
    , mError(aError)
    , mFile(aFile)
    , mWindowID(aWindowID) {}

  NS_IMETHOD
  Run()
  {
    // Only run if the window is still active.
    NS_ASSERTION(NS_IsMainThread(), "Only call on main thread");

    nsCOMPtr<nsIDOMGetUserMediaSuccessCallback> success(mSuccess);
    nsCOMPtr<nsIDOMGetUserMediaErrorCallback> error(mError);

    WindowTable* activeWindows = MediaManager::Get()->GetActiveWindows();
    if (activeWindows->Get(mWindowID)) {
      // XPConnect is a magical unicorn.
      success->OnSuccess(mFile);
    }
    return NS_OK;
  }

private:
  already_AddRefed<nsIDOMGetUserMediaSuccessCallback> mSuccess;
  already_AddRefed<nsIDOMGetUserMediaErrorCallback> mError;
  nsCOMPtr<nsIDOMFile> mFile;
  uint64_t mWindowID;
};

/**
 * Invoke the GetUserMediaDevices success callback. Wrapped in a runnable
 * so that it may be called on the main thread. The error callback is also
 * passed so it can be released correctly.
 */
class DeviceSuccessCallbackRunnable: public nsRunnable
{
public:
  DeviceSuccessCallbackRunnable(
    already_AddRefed<nsIGetUserMediaDevicesSuccessCallback> aSuccess,
    already_AddRefed<nsIDOMGetUserMediaErrorCallback> aError,
    const nsTArray<nsCOMPtr<nsIMediaDevice> >& aDevices)
    : mSuccess(aSuccess)
    , mError(aError)
    , mDevices(aDevices) {}

  NS_IMETHOD
  Run()
  {
    NS_ASSERTION(NS_IsMainThread(), "Only call on main thread");

    nsCOMPtr<nsIGetUserMediaDevicesSuccessCallback> success(mSuccess);
    nsCOMPtr<nsIDOMGetUserMediaErrorCallback> error(mError);

    nsCOMPtr<nsIWritableVariant> devices =
      do_CreateInstance("@mozilla.org/variant;1");

    int32_t len = mDevices.Length();
    if (len == 0) {
      devices->SetAsEmptyArray();
      success->OnSuccess(devices);
      return NS_OK;
    }

    nsTArray<nsIMediaDevice*> tmp(len);
    for (int32_t i = 0; i < len; i++) {
      tmp.AppendElement(mDevices.ElementAt(i));
    }

    devices->SetAsArray(nsIDataType::VTYPE_INTERFACE,
                        &NS_GET_IID(nsIMediaDevice),
                        mDevices.Length(),
                        const_cast<void*>(
                          static_cast<const void*>(tmp.Elements())
                        ));

    success->OnSuccess(devices);
    return NS_OK;
  }

private:
  already_AddRefed<nsIGetUserMediaDevicesSuccessCallback> mSuccess;
  already_AddRefed<nsIDOMGetUserMediaErrorCallback> mError;
  nsTArray<nsCOMPtr<nsIMediaDevice> > mDevices;
};

/**
 * nsIMediaDevice implementation.
 */
NS_IMPL_THREADSAFE_ISUPPORTS1(MediaDevice, nsIMediaDevice)

NS_IMETHODIMP
MediaDevice::GetName(nsAString& aName)
{
  aName.Assign(mName);
  return NS_OK;
}

NS_IMETHODIMP
MediaDevice::GetType(nsAString& aType)
{
  aType.Assign(mType);
  return NS_OK;
}

MediaEngineSource*
MediaDevice::GetSource()
{
  return mSource;
}

/**
 * Creates a MediaStream, attaches a listener and fires off a success callback
 * to the DOM with the stream. We also pass in the error callback so it can
 * be released correctly.
 *
 * All of this must be done on the main thread!
 */
class GetUserMediaStreamRunnable : public nsRunnable
{
public:
  GetUserMediaStreamRunnable(
    already_AddRefed<nsIDOMGetUserMediaSuccessCallback> aSuccess,
    already_AddRefed<nsIDOMGetUserMediaErrorCallback> aError,
    MediaEngineSource* aSource, StreamListeners* aListeners,
    uint64_t aWindowID, TrackID aTrackID)
    : mSuccess(aSuccess)
    , mError(aError)
    , mSource(aSource)
    , mListeners(aListeners)
    , mWindowID(aWindowID)
    , mTrackID(aTrackID) {}

  ~GetUserMediaStreamRunnable() {}

  NS_IMETHOD
  Run()
  {
    NS_ASSERTION(NS_IsMainThread(), "Only call on main thread");

    // Create a media stream.
    nsCOMPtr<nsDOMMediaStream> stream = nsDOMMediaStream::CreateInputStream();

    nsPIDOMWindow *window = static_cast<nsPIDOMWindow*>
      (nsGlobalWindow::GetInnerWindowWithId(mWindowID));

    if (window && window->GetExtantDoc()) {
      stream->CombineWithPrincipal(window->GetExtantDoc()->NodePrincipal());
    }

    // Add our listener. We'll call Start() on the source when get a callback
    // that the MediaStream has started consuming. The listener is freed
    // when the page is invalidated (on navigation or close).
    GetUserMediaCallbackMediaStreamListener* listener =
      new GetUserMediaCallbackMediaStreamListener(mSource, stream, mTrackID);
    stream->GetStream()->AddListener(listener);

    // No need for locking because we always do this in the main thread.
    mListeners->AppendElement(listener);

    // We're in the main thread, so no worries here either.
    nsCOMPtr<nsIDOMGetUserMediaSuccessCallback> success(mSuccess);
    nsCOMPtr<nsIDOMGetUserMediaErrorCallback> error(mError);

    WindowTable* activeWindows = MediaManager::Get()->GetActiveWindows();
    if (activeWindows->Get(mWindowID)) {
      success->OnSuccess(stream);
    }

    return NS_OK;
  }

private:
  already_AddRefed<nsIDOMGetUserMediaSuccessCallback> mSuccess;
  already_AddRefed<nsIDOMGetUserMediaErrorCallback> mError;
  nsRefPtr<MediaEngineSource> mSource;
  StreamListeners* mListeners;
  uint64_t mWindowID;
  TrackID mTrackID;
};

/**
 * Runs on a seperate thread and is responsible for enumerating devices.
 * Depending on whether a picture or stream was asked for, either
 * ProcessGetUserMedia or ProcessGetUserMediaSnapshot is called, and the results
 * are sent back to the DOM.
 *
 * Do not run this on the main thread. The success and error callbacks *MUST*
 * be dispatched on the main thread!
 */
class GetUserMediaRunnable : public nsRunnable
{
public:
  /**
   * The caller can choose to provide a MediaDevice as the last argument,
   * if one is not provided, a default device is automatically chosen.
   */
  GetUserMediaRunnable(bool aAudio, bool aVideo, bool aPicture,
    already_AddRefed<nsIDOMGetUserMediaSuccessCallback> aSuccess,
    already_AddRefed<nsIDOMGetUserMediaErrorCallback> aError,
    StreamListeners* aListeners, uint64_t aWindowID, MediaDevice* aDevice)
    : mAudio(aAudio)
    , mVideo(aVideo)
    , mPicture(aPicture)
    , mSuccess(aSuccess)
    , mError(aError)
    , mListeners(aListeners)
    , mWindowID(aWindowID)
    , mDevice(aDevice)
    , mDeviceChosen(true)
    , mBackendChosen(false) {}

  GetUserMediaRunnable(bool aAudio, bool aVideo, bool aPicture,
    already_AddRefed<nsIDOMGetUserMediaSuccessCallback> aSuccess,
    already_AddRefed<nsIDOMGetUserMediaErrorCallback> aError,
    StreamListeners* aListeners, uint64_t aWindowID)
    : mAudio(aAudio)
    , mVideo(aVideo)
    , mPicture(aPicture)
    , mSuccess(aSuccess)
    , mError(aError)
    , mListeners(aListeners)
    , mWindowID(aWindowID)
    , mDeviceChosen(false)
    , mBackendChosen(false) {}

  /**
   * The caller can also choose to provide their own backend instead of
   * using the one provided by MediaManager::GetBackend.
   */
  GetUserMediaRunnable(bool aAudio, bool aVideo,
    already_AddRefed<nsIDOMGetUserMediaSuccessCallback> aSuccess,
    already_AddRefed<nsIDOMGetUserMediaErrorCallback> aError,
    StreamListeners* aListeners, uint64_t aWindowID, MediaEngine* aBackend)
    : mAudio(aAudio)
    , mVideo(aVideo)
    , mPicture(false)
    , mSuccess(aSuccess)
    , mError(aError)
    , mListeners(aListeners)
    , mWindowID(aWindowID)
    , mDeviceChosen(false)
    , mBackendChosen(true)
    , mBackend(aBackend) {}

  ~GetUserMediaRunnable() {
    if (mBackendChosen) {
      delete mBackend;
    }
  }

  // We only support 1 audio and 1 video track for now.
  enum {
    kVideoTrack = 1,
    kAudioTrack = 2
  };

  NS_IMETHOD
  Run()
  {
    NS_ASSERTION(!NS_IsMainThread(), "Don't call on main thread");

    mManager = MediaManager::Get();

    // Was a backend provided?
    if (!mBackendChosen) {
      mBackend = mManager->GetBackend();
    }

    // Was a device provided?
    if (!mDeviceChosen) {
      nsresult rv = SelectDevice();
      if (rv != NS_OK) {
        return rv;
      }
    }

    // It is an error if audio or video are requested along with picture.
    if (mPicture && (mAudio || mVideo)) {
      NS_DispatchToMainThread(new ErrorCallbackRunnable(
        mSuccess, mError, NS_LITERAL_STRING("NOT_SUPPORTED_ERR"), mWindowID
      ));
      return NS_OK;
    }

    // XXX: Implement merging two streams (See bug 758391).
    if (mAudio && mVideo) {
      NS_DispatchToMainThread(new ErrorCallbackRunnable(
        mSuccess, mError, NS_LITERAL_STRING("NOT_IMPLEMENTED"), mWindowID
      ));
      return NS_OK;
    }

    if (mPicture) {
      ProcessGetUserMediaSnapshot(mDevice->GetSource(), 0);
      return NS_OK;
    }

    if (mVideo) {
      ProcessGetUserMedia(mDevice->GetSource(), kVideoTrack);
      return NS_OK;
    }

    if (mAudio) {
      ProcessGetUserMedia(mDevice->GetSource(), kAudioTrack);
      return NS_OK;
    }

    return NS_OK;
  }

  nsresult
  SelectDevice()
  {
    uint32_t count;
    if (mPicture || mVideo) {
      nsTArray<nsRefPtr<MediaEngineVideoSource> > videoSources;
      mBackend->EnumerateVideoDevices(&videoSources);

      count = videoSources.Length();
      if (count <= 0) {
        NS_DispatchToMainThread(new ErrorCallbackRunnable(
          mSuccess, mError, NS_LITERAL_STRING("NO_DEVICES_FOUND"), mWindowID
        ));
        return NS_ERROR_FAILURE;
      }
      mDevice = new MediaDevice(videoSources[0]);
    } else {
      nsTArray<nsRefPtr<MediaEngineAudioSource> > audioSources;
      mBackend->EnumerateAudioDevices(&audioSources);

      count = audioSources.Length();
      if (count <= 0) {
        NS_DispatchToMainThread(new ErrorCallbackRunnable(
          mSuccess, mError, NS_LITERAL_STRING("NO_DEVICES_FOUND"), mWindowID
        ));
        return NS_ERROR_FAILURE;
      }
      mDevice = new MediaDevice(audioSources[0]);
    }

    return NS_OK;
  }

  /**
   * Allocates a video or audio device and returns a MediaStream via
   * a GetUserMediaStreamRunnable. Runs off the main thread.
   */
  void
  ProcessGetUserMedia(MediaEngineSource* aSource, TrackID aTrackID)
  {
    nsresult rv = aSource->Allocate();
    if (NS_FAILED(rv)) {
      NS_DispatchToMainThread(new ErrorCallbackRunnable(
        mSuccess, mError, NS_LITERAL_STRING("HARDWARE_UNAVAILABLE"), mWindowID
      ));
      return;
    }

    NS_DispatchToMainThread(new GetUserMediaStreamRunnable(
      mSuccess, mError, aSource, mListeners, mWindowID, aTrackID
    ));
    return;
  }

  /**
   * Allocates a video device, takes a snapshot and returns a DOMFile via
   * a SuccessRunnable or an error via the ErrorRunnable. Off the main thread.
   */
  void
  ProcessGetUserMediaSnapshot(MediaEngineSource* aSource, int aDuration)
  {
    nsresult rv = aSource->Allocate();
    if (NS_FAILED(rv)) {
      NS_DispatchToMainThread(new ErrorCallbackRunnable(
        mSuccess, mError, NS_LITERAL_STRING("HARDWARE_UNAVAILABLE"), mWindowID
      ));
      return;
    }

    /**
     * Display picture capture UI here before calling Snapshot() - Bug 748835.
     */
    nsCOMPtr<nsIDOMFile> file;
    aSource->Snapshot(aDuration, getter_AddRefs(file));
    aSource->Deallocate();

    NS_DispatchToMainThread(new SuccessCallbackRunnable(
      mSuccess, mError, file, mWindowID
    ));
    return;
  }

private:
  bool mAudio;
  bool mVideo;
  bool mPicture;

  already_AddRefed<nsIDOMGetUserMediaSuccessCallback> mSuccess;
  already_AddRefed<nsIDOMGetUserMediaErrorCallback> mError;
  StreamListeners* mListeners;
  uint64_t mWindowID;
  nsRefPtr<MediaDevice> mDevice;

  bool mDeviceChosen;
  bool mBackendChosen;

  MediaEngine* mBackend;
  MediaManager* mManager;
};

/**
 * Similar to GetUserMediaRunnable, but used for the chrome-only
 * GetUserMediaDevices function. Enumerates a list of audio & video devices,
 * wraps them up in nsIMediaDevice objects and returns it to the success
 * callback.
 */
class GetUserMediaDevicesRunnable : public nsRunnable
{
public:
  GetUserMediaDevicesRunnable(
    already_AddRefed<nsIGetUserMediaDevicesSuccessCallback> aSuccess,
    already_AddRefed<nsIDOMGetUserMediaErrorCallback> aError)
    : mSuccess(aSuccess)
    , mError(aError) {}
  ~GetUserMediaDevicesRunnable() {}

  NS_IMETHOD
  Run()
  {
    NS_ASSERTION(!NS_IsMainThread(), "Don't call on main thread");

    uint32_t audioCount, videoCount, i;
    MediaManager* manager = MediaManager::Get();

    nsTArray<nsRefPtr<MediaEngineVideoSource> > videoSources;
    manager->GetBackend()->EnumerateVideoDevices(&videoSources);
    videoCount = videoSources.Length();

    nsTArray<nsRefPtr<MediaEngineAudioSource> > audioSources;
    manager->GetBackend()->EnumerateAudioDevices(&audioSources);
    audioCount = videoSources.Length();

    nsTArray<nsCOMPtr<nsIMediaDevice> > *devices =
      new nsTArray<nsCOMPtr<nsIMediaDevice> >;

    for (i = 0; i < videoCount; i++) {
      devices->AppendElement(new MediaDevice(videoSources[i]));
    }
    for (i = 0; i < audioCount; i++) {
      devices->AppendElement(new MediaDevice(audioSources[i]));
    }

    NS_DispatchToMainThread(new DeviceSuccessCallbackRunnable(
      mSuccess, mError, *devices
    ));
    return NS_OK;
  }

private:
  already_AddRefed<nsIGetUserMediaDevicesSuccessCallback> mSuccess;
  already_AddRefed<nsIDOMGetUserMediaErrorCallback> mError;
};

nsRefPtr<MediaManager> MediaManager::sSingleton;

NS_IMPL_THREADSAFE_ISUPPORTS1(MediaManager, nsIObserver)

/**
 * The entry point for this file. A call from Navigator::mozGetUserMedia
 * will end up here. MediaManager is a singleton that is responsible
 * for handling all incoming getUserMedia calls from every window.
 */
nsresult
MediaManager::GetUserMedia(bool aPrivileged, nsPIDOMWindow* aWindow,
  nsIMediaStreamOptions* aParams,
  nsIDOMGetUserMediaSuccessCallback* aOnSuccess,
  nsIDOMGetUserMediaErrorCallback* aOnError)
{
  NS_ASSERTION(NS_IsMainThread(), "Only call on main thread");

  NS_ENSURE_TRUE(aParams, NS_ERROR_NULL_POINTER);
  NS_ENSURE_TRUE(aWindow, NS_ERROR_NULL_POINTER);

  nsCOMPtr<nsIDOMGetUserMediaSuccessCallback> onSuccess(aOnSuccess);
  nsCOMPtr<nsIDOMGetUserMediaErrorCallback> onError(aOnError);

  /* Get options */
  nsresult rv;
  bool fake, audio, video, picture;

  rv = aParams->GetFake(&fake);
  NS_ENSURE_SUCCESS(rv, rv);

  rv = aParams->GetPicture(&picture);
  NS_ENSURE_SUCCESS(rv, rv);

  rv = aParams->GetAudio(&audio);
  NS_ENSURE_SUCCESS(rv, rv);

  rv = aParams->GetVideo(&video);
  NS_ENSURE_SUCCESS(rv, rv);

  nsCOMPtr<nsIMediaDevice> device;
  rv = aParams->GetDevice(getter_AddRefs(device));
  NS_ENSURE_SUCCESS(rv, rv);

  // If a device was provided, make sure it support the type of stream requested.
  if (device) {
    nsString type;
    device->GetType(type);
    if ((picture || video) && !type.EqualsLiteral("video")) {
      return NS_ERROR_FAILURE;
    }
    if (audio && !type.EqualsLiteral("audio")) {
      return NS_ERROR_FAILURE;
    }
  }

  // We only support "front" or "back". TBD: Send to GetUserMediaRunnable.
  nsString cameraType;
  rv = aParams->GetCamera(cameraType);
  NS_ENSURE_SUCCESS(rv, rv);

  /**
   * If we were asked to get a picture, before getting a snapshot, we check if
   * the calling page is allowed to open a popup. We do this because
   * {picture:true} will open a new "window" to let the user preview or select
   * an image, on Android. The desktop UI for {picture:true} is TBD, at which
   * may point we can decide whether to extend this test there as well.
   */
#if !defined(MOZ_WEBRTC)
  if (picture && !aPrivileged) {
    if (aWindow->GetPopupControlState() > openControlled) {
      nsCOMPtr<nsIPopupWindowManager> pm =
        do_GetService(NS_POPUPWINDOWMANAGER_CONTRACTID);
      if (!pm) {
        return NS_OK;
      }
      uint32_t permission;
      nsCOMPtr<nsIDocument> doc = aWindow->GetExtantDoc();
      pm->TestPermission(doc->NodePrincipal(), &permission);
      if ((permission == nsIPopupWindowManager::DENY_POPUP)) {
        nsCOMPtr<nsIDOMDocument> domDoc = aWindow->GetExtantDocument();
        nsGlobalWindow::FirePopupBlockedEvent(
          domDoc, aWindow, nullptr, EmptyString(), EmptyString()
        );
        return NS_OK;
      }
    }
  }
#endif

  /**
   * UI integration point. Check for permission with the user!
   * No UI for picture:true here, since user permission is implied by the
   * preview dialog that will be shown by GetUserMediaRunnable in SendPicture.
   */
  if (!aPrivileged && !picture) {
    // To be filled in by code from bug 729522. If permission is denied, call
    // onError, and do not continue.
  }

  // Store the WindowID in a hash table and mark as active. The entry is removed
  // when this window is closed or navigated away from.
  uint64_t windowID = aWindow->WindowID();
  StreamListeners* listeners = mActiveWindows.Get(windowID);
  if (!listeners) {
    listeners = new StreamListeners;
    mActiveWindows.Put(windowID, listeners);
  }

  /**
   * Pass runnables along to GetUserMediaRunnable so it can add the
   * MediaStreamListener to the runnable list. The last argument can
   * optionally be a MediaDevice object, which should provided if one was
   * selected by the user via the UI, or was provided by privileged code
   * via the device: attribute via nsIMediaStreamOptions.
   *
   * If a fake stream was requested, we force the use of the default backend.
   */
  nsCOMPtr<nsIRunnable> gUMRunnable;
  if (fake) {
    // Fake stream from default backend.
    gUMRunnable = new GetUserMediaRunnable(
      audio, video, onSuccess.forget(), onError.forget(), listeners,
      windowID, new MediaEngineDefault()
    );
  } else if (device) {
    // Stream from provided device.
    gUMRunnable = new GetUserMediaRunnable(
      audio, video, picture, onSuccess.forget(), onError.forget(), listeners,
      windowID, static_cast<MediaDevice*>(device.get())
    );
  } else {
    // Stream from default device from WebRTC backend.
    gUMRunnable = new GetUserMediaRunnable(
      audio, video, picture, onSuccess.forget(), onError.forget(), listeners,
      windowID
    );
  }

  if (picture) {
    // ShowFilePickerForMimeType() must run on the Main Thread! (on Android)
    NS_DispatchToMainThread(gUMRunnable);
  } else {
    // Reuse the same thread to save memory.
    if (!mMediaThread) {
      rv = NS_NewThread(getter_AddRefs(mMediaThread));
      NS_ENSURE_SUCCESS(rv, rv);
    }

    mMediaThread->Dispatch(gUMRunnable, NS_DISPATCH_NORMAL);
  }
  return NS_OK;
}

nsresult
MediaManager::GetUserMediaDevices(nsPIDOMWindow* aWindow,
  nsIGetUserMediaDevicesSuccessCallback* aOnSuccess,
  nsIDOMGetUserMediaErrorCallback* aOnError)
{
  NS_ASSERTION(NS_IsMainThread(), "Only call on main thread");

  nsCOMPtr<nsIGetUserMediaDevicesSuccessCallback> onSuccess(aOnSuccess);
  nsCOMPtr<nsIDOMGetUserMediaErrorCallback> onError(aOnError);

  nsCOMPtr<nsIRunnable> gUMDRunnable = new GetUserMediaDevicesRunnable(
    onSuccess.forget(), onError.forget()
  );

  nsCOMPtr<nsIThread> deviceThread;
  nsresult rv = NS_NewThread(getter_AddRefs(deviceThread));
  NS_ENSURE_SUCCESS(rv, rv);


  deviceThread->Dispatch(gUMDRunnable, NS_DISPATCH_NORMAL);
  return NS_OK;
}

MediaEngine*
MediaManager::GetBackend()
{
  // Plugin backends as appropriate. The default engine also currently
  // includes picture support for Android.
  if (!mBackend) {
#if defined(MOZ_WEBRTC)
    mBackend = new MediaEngineWebRTC();
#else
    mBackend = new MediaEngineDefault();
#endif
  }

  return mBackend;
}

WindowTable*
MediaManager::GetActiveWindows()
{
  return &mActiveWindows;
}

void
MediaManager::OnNavigation(uint64_t aWindowID)
{
  // Invalidate this window. The runnables check this value before making
  // a call to content.
  StreamListeners* listeners = mActiveWindows.Get(aWindowID);
  if (!listeners) {
    return;
  }

  uint32_t length = listeners->Length();
  for (uint32_t i = 0; i < length; i++) {
    nsRefPtr<GetUserMediaCallbackMediaStreamListener> listener =
      listeners->ElementAt(i);
    listener->Invalidate();
    listener = nullptr;
  }
  listeners->Clear();

  mActiveWindows.Remove(aWindowID);
}

nsresult
MediaManager::Observe(nsISupports* aSubject, const char* aTopic,
  const PRUnichar* aData)
{
  if (strcmp(aTopic, "xpcom-shutdown")) {
    return NS_OK;
  }

  nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
  obs->RemoveObserver(this, "xpcom-shutdown");

  // Close off any remaining active windows.
  mActiveWindows.Clear();
  sSingleton = nullptr;

  return NS_OK;
}

} // namespace mozilla