author Sylvestre Ledru <>
Mon, 05 Mar 2018 13:43:54 +0100
changeset 461635 53bdcd5937cdb1ccf4388ee7a0f3fee0c3675c52
parent 456145 246493ebf8627765eaa25e1ad4ce91c7acff8354
child 461641 b1117fa567eb9067f2816a813046a129406f20cf
permissions -rw-r--r--
Bug 1443080 - Use the static call for static methods (not instance) r=Ehsan MozReview-Commit-ID: JwHh4bzxuTR

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set sw=2 ts=8 et ft=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 */

#ifndef mozilla_CamerasChild_h
#define mozilla_CamerasChild_h

#include "mozilla/Move.h"
#include "mozilla/Pair.h"
#include "mozilla/dom/ContentChild.h"
#include "mozilla/camera/PCamerasChild.h"
#include "mozilla/camera/PCamerasParent.h"
#include "mozilla/media/DeviceChangeCallback.h"
#include "mozilla/Mutex.h"
#include "base/singleton.h"
#include "nsCOMPtr.h"

// conflicts with #include of scoped_ptr.h
#undef FF
#include "webrtc/modules/video_capture/video_capture_defines.h"

namespace mozilla {

namespace ipc {
class BackgroundChildImpl;
class PrincipalInfo;

namespace camera {

class FrameRelay {
  virtual int DeliverFrame(uint8_t* buffer,
    const mozilla::camera::VideoFrameProperties& props) = 0;

struct CapturerElement {
  CaptureEngine engine;
  int id;
  FrameRelay* callback;

// Forward declaration so we can work with pointers to it.
class CamerasChild;
// Helper class in impl that we friend.
template <class T> class LockAndDispatch;

// We emulate the sync API with the help of singleton
// CamerasSingleton, which manages a pointer to an IPC object, a thread
// where IPC operations should run on, and a mutex.
// The static function Cameras() will use that Singleton to set up,
// if needed, both the thread and the associated IPC objects and return
// a pointer to the IPC object. Users can then do IPC calls on that object
// after dispatching them to aforementioned thread.

// 2 Threads are involved in this code:
// - the MediaManager thread, which will call the (static, sync API) functions
//   through MediaEngineRemoteVideoSource
// - the Cameras IPC thread, which will be doing our IPC to the parent process
//   via PBackground

// Our main complication is that we emulate a sync API while (having to do)
// async messaging. We dispatch the messages to another thread to send them
// async and hold a Monitor to wait for the result to be asynchronously received
// again. The requirement for async messaging originates on the parent side:
// it's not reasonable to block all PBackground IPC there while waiting for
// something like device enumeration to complete.

class CamerasSingleton {

  static OffTheBooksMutex& Mutex() {
    return Singleton<mozilla::camera::CamerasSingleton>::get()->mCamerasMutex;

  static CamerasChild*& Child() {
    return Singleton<mozilla::camera::CamerasSingleton>::get()->mCameras;

  static nsCOMPtr<nsIThread>& Thread() {
    return Singleton<mozilla::camera::CamerasSingleton>::get()->mCamerasChildThread;

  static nsCOMPtr<nsIThread>& FakeDeviceChangeEventThread() {
    return Singleton<mozilla::camera::CamerasSingleton>::get()->mFakeDeviceChangeEventThread;

  static bool InShutdown() {
    return gTheInstance.get()->mInShutdown;

  static void StartShutdown() {
    gTheInstance.get()->mInShutdown = true;

  static Singleton<CamerasSingleton> gTheInstance;

  // Reinitializing CamerasChild will change the pointers below.
  // We don't want this to happen in the middle of preparing IPC.
  // We will be alive on destruction, so this needs to be off the books.
  mozilla::OffTheBooksMutex mCamerasMutex;

  // This is owned by the IPC code, and the same code controls the lifetime.
  // It will set and clear this pointer as appropriate in setup/teardown.
  // We'd normally make this a WeakPtr but unfortunately the IPC code already
  // uses the WeakPtr mixin in a protected base class of CamerasChild, and in
  // any case the object becomes unusable as soon as IPC is tearing down, which
  // will be before actual destruction.
  CamerasChild* mCameras;
  nsCOMPtr<nsIThread> mCamerasChildThread;
  nsCOMPtr<nsIThread> mFakeDeviceChangeEventThread;
  Atomic<bool> mInShutdown;

// Get a pointer to a CamerasChild object we can use to do IPC with.
// This does everything needed to set up, including starting the IPC
// channel with PBackground, blocking until thats done, and starting the
// thread to do IPC on. This will fail if we're in shutdown. On success
// it will set up the CamerasSingleton.
CamerasChild* GetCamerasChild();

CamerasChild* GetCamerasChildIfExists();

// Shut down the IPC channel and everything associated, like WebRTC.
// This is a static call because the CamerasChild object may not even
// be alive when we're called.
void Shutdown(void);

// Obtain the CamerasChild object (if possible, i.e. not shutting down),
// and maintain a grip on the object for the duration of the call.
template <class MEM_FUN, class... ARGS>
int GetChildAndCall(MEM_FUN&& f, ARGS&&... args)
  OffTheBooksMutexAutoLock lock(CamerasSingleton::Mutex());
  CamerasChild* child = GetCamerasChild();
  if (child) {
    return (child->*f)(mozilla::Forward<ARGS>(args)...);
  } else {
    return -1;

class CamerasChild final : public PCamerasChild
                          ,public DeviceChangeCallback
  friend class mozilla::ipc::BackgroundChildImpl;
  template <class T> friend class mozilla::camera::LockAndDispatch;

  // We are owned by the PBackground thread only. CamerasSingleton
  // takes a non-owning reference.

  // IPC messages recevied, received on the PBackground thread
  // these are the actual callbacks with data
  mozilla::ipc::IPCResult RecvDeliverFrame(const CaptureEngine&, const int&,
                                           const VideoFrameProperties & prop) override;

  mozilla::ipc::IPCResult RecvDeviceChange() override;
  int AddDeviceChangeCallback(DeviceChangeCallback* aCallback) override;
  int SetFakeDeviceChangeEvents();

  // these are response messages to our outgoing requests
  mozilla::ipc::IPCResult RecvReplyNumberOfCaptureDevices(const int&) override;
  mozilla::ipc::IPCResult RecvReplyNumberOfCapabilities(const int&) override;
  mozilla::ipc::IPCResult RecvReplyAllocateCaptureDevice(const int&) override;
  mozilla::ipc::IPCResult RecvReplyGetCaptureCapability(const VideoCaptureCapability& capability) override;
  mozilla::ipc::IPCResult RecvReplyGetCaptureDevice(const nsCString& device_name,
                                                            const nsCString& device_id,
                                                            const bool& scary) override;
  mozilla::ipc::IPCResult RecvReplyFailure(void) override;
  mozilla::ipc::IPCResult RecvReplySuccess(void) override;
  void ActorDestroy(ActorDestroyReason aWhy) override;

  // the ViECapture calls are mirrored here, but with access
  // to a specific PCameras instance to communicate over. These also
  // run on the MediaManager thread
  int NumberOfCaptureDevices(CaptureEngine aCapEngine);
  int NumberOfCapabilities(CaptureEngine aCapEngine,
                           const char* deviceUniqueIdUTF8);
  int ReleaseCaptureDevice(CaptureEngine aCapEngine,
                           const int capture_id);
  int StartCapture(CaptureEngine aCapEngine,
                   const int capture_id, webrtc::VideoCaptureCapability& capability,
                   FrameRelay* func);
  int StopCapture(CaptureEngine aCapEngine, const int capture_id);
  int AllocateCaptureDevice(CaptureEngine aCapEngine,
                            const char* unique_idUTF8,
                            const unsigned int unique_idUTF8Length,
                            int& capture_id,
                            const mozilla::ipc::PrincipalInfo& aPrincipalInfo);
  int GetCaptureCapability(CaptureEngine aCapEngine,
                           const char* unique_idUTF8,
                           const unsigned int capability_number,
                           webrtc::VideoCaptureCapability& capability);
  int GetCaptureDevice(CaptureEngine aCapEngine,
                       unsigned int list_number, char* device_nameUTF8,
                       const unsigned int device_nameUTF8Length,
                       char* unique_idUTF8,
                       const unsigned int unique_idUTF8Length,
                       bool* scary = nullptr);
  void ShutdownAll();
  int EnsureInitialized(CaptureEngine aCapEngine);

  FrameRelay* Callback(CaptureEngine aCapEngine, int capture_id);

  // Dispatch a Runnable to the PCamerasParent, by executing it on the
  // decidecated Cameras IPC/PBackground thread.
  bool DispatchToParent(nsIRunnable* aRunnable,
                        MonitorAutoLock& aMonitor);
  void AddCallback(const CaptureEngine aCapEngine, const int capture_id,
                   FrameRelay* render);
  void RemoveCallback(const CaptureEngine aCapEngine, const int capture_id);
  void ShutdownParent();
  void ShutdownChild();

  nsTArray<CapturerElement> mCallbacks;
  // Protects the callback arrays
  Mutex mCallbackMutex;

  bool mIPCIsAlive;

  // Hold to prevent multiple outstanding requests. We don't use
  // request IDs so we only support one at a time. Don't want try
  // to use the API from multiple threads simultanously.
  // The monitor below isn't sufficient for this, as it will drop
  // the lock when Wait-ing for a response, allowing us to send a new
  // request. The Notify on receiving the response will then unblock
  // both waiters and one will be guaranteed to get the wrong result.
  // Take this one before taking mReplyMonitor.
  Mutex mRequestMutex;
  // Hold to wait for an async response to our calls
  Monitor mReplyMonitor;
  // Async response valid?
  bool mReceivedReply;
  // Async responses data contents;
  bool mReplySuccess;
  const int mZero;
  int mReplyInteger;
  webrtc::VideoCaptureCapability mReplyCapability;
  nsCString mReplyDeviceName;
  nsCString mReplyDeviceID;
  bool mReplyScary;

} // namespace camera
} // namespace mozilla

#endif  // mozilla_CamerasChild_h