gecko-dev/dom/media/systemservices/CamerasChild.h

/* -*- 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 http://mozilla.org/MPL/2.0/. */

#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/Mutex.h"
#include "base/singleton.h"
#include "nsCOMPtr.h"

// conflicts with #include of scoped_ptr.h
#undef FF
#include "webrtc/common.h"
// Video Engine
#include "webrtc/video_engine/include/vie_base.h"
#include "webrtc/video_engine/include/vie_capture.h"
#include "webrtc/video_engine/include/vie_render.h"

namespace mozilla {

namespace ipc {
class BackgroundChildImpl;
}

namespace camera {

enum CaptureEngine : int {
  InvalidEngine = 0,
  ScreenEngine,
  BrowserEngine,
  WinEngine,
  AppEngine,
  CameraEngine,
  MaxEngine
};

struct CapturerElement {
  CaptureEngine engine;
  int id;
  webrtc::ExternalRenderer* 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 webrtc.org 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 {
public:
  CamerasSingleton();
  ~CamerasSingleton();

  static OffTheBooksMutex& Mutex() {
    return gTheInstance.get()->mCamerasMutex;
  }

  static CamerasChild*& Child() {
    Mutex().AssertCurrentThreadOwns();
    return gTheInstance.get()->mCameras;
  }

  static nsCOMPtr<nsIThread>& Thread() {
    Mutex().AssertCurrentThreadOwns();
    return gTheInstance.get()->mCamerasChildThread;
  }

private:
  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;
};

// 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();

// 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
{
  friend class mozilla::ipc::BackgroundChildImpl;
  template <class T> friend class mozilla::camera::LockAndDispatch;

public:
  // We are owned by the PBackground thread only. CamerasSingleton
  // takes a non-owning reference.
  NS_INLINE_DECL_REFCOUNTING(CamerasChild)

  // IPC messages recevied, received on the PBackground thread
  // these are the actual callbacks with data
  virtual bool RecvDeliverFrame(const int&, const int&, mozilla::ipc::Shmem&&,
                                const size_t&, const uint32_t&, const int64_t&,
                                const int64_t&) override;
  virtual bool RecvFrameSizeChange(const int&, const int&,
                                   const int& w, const int& h) override;

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

  // the webrtc.org 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::CaptureCapability& capability,
                   webrtc::ExternalRenderer* 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 nsACString& aOrigin);
  int GetCaptureCapability(CaptureEngine aCapEngine,
                           const char* unique_idUTF8,
                           const unsigned int capability_number,
                           webrtc::CaptureCapability& 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);
  void ShutdownAll();

  webrtc::ExternalRenderer* Callback(CaptureEngine aCapEngine, int capture_id);

private:
  CamerasChild();
  ~CamerasChild();
  // 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,
                   webrtc::ExternalRenderer* 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 webrtc.org 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;
  int mReplyInteger;
  webrtc::CaptureCapability mReplyCapability;
  nsCString mReplyDeviceName;
  nsCString mReplyDeviceID;
};

} // namespace camera
} // namespace mozilla

#endif  // mozilla_CamerasChild_h