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diff --git a/dom/media/webrtc/CubebDeviceEnumerator.h b/dom/media/webrtc/CubebDeviceEnumerator.h
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+++ b/dom/media/webrtc/CubebDeviceEnumerator.h
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+/* 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 CUBEBDEVICEENUMERATOR_H_
+#define CUBEBDEVICEENUMERATOR_H_
+
+#include "AudioDeviceInfo.h"
+#include "cubeb/cubeb.h"
+#include "MediaEventSource.h"
+#include "mozilla/Mutex.h"
+#include "nsTArray.h"
+
+namespace mozilla {
+
+namespace media {
+template <typename T>
+class Refcountable;
+}
+
+// This class implements a cache for accessing the audio device list.
+// It can be accessed on any thread.
+class CubebDeviceEnumerator final {
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(CubebDeviceEnumerator)
+
+  static CubebDeviceEnumerator* GetInstance();
+  static void Shutdown();
+  using AudioDeviceSet = media::Refcountable<nsTArray<RefPtr<AudioDeviceInfo>>>;
+  // This method returns a list of all the input audio devices
+  // (sources) available on this machine.
+  // This method is safe to call from all threads.
+  RefPtr<const AudioDeviceSet> EnumerateAudioInputDevices();
+  // Similar for the audio audio devices (sinks). Also thread safe.
+  RefPtr<const AudioDeviceSet> EnumerateAudioOutputDevices();
+  // From a device name, return the info for this device, if it's a valid name,
+  // or nullptr otherwise.
+  // This method is safe to call from any thread.
+  enum class Side {
+    INPUT,
+    OUTPUT,
+  };
+  already_AddRefed<AudioDeviceInfo> DeviceInfoFromName(const nsString& aName,
+                                                       Side aSide);
+  // Event source to listen for changes to the audio input device list on.
+  MediaEventSource<void>& OnAudioInputDeviceListChange() {
+    return mOnInputDeviceListChange;
+  }
+
+  // Event source to listen for changes to the audio output device list on.
+  MediaEventSource<void>& OnAudioOutputDeviceListChange() {
+    return mOnOutputDeviceListChange;
+  }
+
+  // Return the default device for a particular side.
+  RefPtr<AudioDeviceInfo> DefaultDevice(Side aSide);
+
+ private:
+  CubebDeviceEnumerator();
+  ~CubebDeviceEnumerator();
+  // Static functions called by cubeb when the audio device list changes
+  // (i.e. when a new device is made available, or non-available). This
+  // simply calls `AudioDeviceListChanged` below.
+  static void InputAudioDeviceListChanged_s(cubeb* aContext, void* aUser);
+  static void OutputAudioDeviceListChanged_s(cubeb* aContext, void* aUser);
+  // Invalidates the cached audio input device list, can be called on any
+  // thread.
+  void AudioDeviceListChanged(Side aSide);
+  RefPtr<const AudioDeviceSet> EnumerateAudioDevices(Side aSide);
+  // Synchronize access to mInputDevices and mOutputDevices;
+  Mutex mMutex MOZ_UNANNOTATED;
+  RefPtr<const AudioDeviceSet> mInputDevices;
+  RefPtr<const AudioDeviceSet> mOutputDevices;
+  // If mManual*Invalidation is true, then it is necessary to query the device
+  // list each time instead of relying on automatic invalidation of the cache by
+  // cubeb itself. Set in the constructor and then can be access on any thread.
+  bool mManualInputInvalidation;
+  bool mManualOutputInvalidation;
+  MediaEventProducer<void> mOnInputDeviceListChange;
+  MediaEventProducer<void> mOnOutputDeviceListChange;
+};
+
+typedef CubebDeviceEnumerator Enumerator;
+typedef CubebDeviceEnumerator::Side EnumeratorSide;
+}  // namespace mozilla
+
+#endif  // CUBEBDEVICEENUMERATOR_H_