Web MIDI backend for Windows 10

media/midi/midi_manager_winrt.cc

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "media/midi/midi_manager_winrt.h"
+
+#include <comdef.h>
+#include <robuffer.h>
+#include <windows.devices.enumeration.h>
+#include <windows.devices.midi.h>
+#include <wrl/event.h>
+
+#include <iomanip>
+#include <unordered_map>
+#include <unordered_set>
+
+#include "base/bind.h"
+#include "base/strings/utf_string_conversions.h"
+#include "base/threading/thread_checker.h"
+#include "base/threading/thread_task_runner_handle.h"
+#include "base/timer/timer.h"
+#include "base/win/scoped_comptr.h"
+#include "base/win/windows_version.h"
+#include "media/midi/midi_scheduler.h"
+
+namespace media {
+namespace midi {
+namespace {
+
+namespace WRL = Microsoft::WRL;
+
+using namespace ABI::Windows::Devices::Enumeration;
+using namespace ABI::Windows::Devices::Midi;
+using namespace ABI::Windows::Foundation;
+using namespace ABI::Windows::Storage::Streams;
+
+using base::win::ScopedComPtr;
+
+// Helpers for printing HRESULTs.
+struct PrintHr {
+  PrintHr(HRESULT hr) : hr_(hr) {}
+  HRESULT hr_;

[Takashi Toyoshima, 2016/08/29 16:20:17]

I overlooked this style nit, but we do not use underbar suffix for struct
members.

[Shao-Chuan Lee, 2016/08/30 02:37:48]

Done.

+};
+
+std::ostream& operator<<(std::ostream& os, const PrintHr& phr) {
+  std::ios_base::fmtflags ff = os.flags();
+  os << _com_error(phr.hr_).ErrorMessage() << " (0x" << std::hex
+     << std::uppercase << std::setfill('0') << std::setw(8) << phr.hr_ << ")";
+  os.flags(ff);
+  return os;
+}
+
+// Factory functions that activate and create WinRT components. The caller takes
+// ownership of the returning ComPtr.
+template <typename InterfaceType, base::char16 const* runtime_class_id>
+ScopedComPtr<InterfaceType> WrlStaticsFactory() {
+  ScopedComPtr<InterfaceType> com_ptr;
+
+  HRESULT hr = GetActivationFactory(
+      WRL::Wrappers::HStringReference(runtime_class_id).Get(),
+      com_ptr.Receive());
+  if (FAILED(hr)) {
+    VLOG(1) << "GetActivationFactory failed: " << PrintHr(hr);
+    com_ptr = nullptr;
+  }
+
+  return com_ptr;
+}
+
+template <typename T, HRESULT (T::*method)(HSTRING*)>
+std::string GetStringFromObjectMethod(T* obj) {
+  HSTRING result;
+  HRESULT hr = (obj->*method)(&result);
+  if (FAILED(hr)) {
+    VLOG(1) << "GetStringFromObjectMethod failed: " << PrintHr(hr);
+    return std::string();
+  }
+
+  // Note: empty HSTRINGs are represent as nullptr, and instantiating
+  // std::string with nullptr (in base::WideToUTF8) is undefined behavior.
+  const base::char16* buffer = WindowsGetStringRawBuffer(result, nullptr);
+  if (buffer)
+    return base::WideToUTF8(buffer);
+  return std::string();
+}
+
+template <typename T>
+std::string GetIdString(T* obj) {
+  return GetStringFromObjectMethod<T, &T::get_Id>(obj);
+}
+
+template <typename T>
+std::string GetDeviceIdString(T* obj) {
+  return GetStringFromObjectMethod<T, &T::get_DeviceId>(obj);
+}
+
+std::string GetNameString(IDeviceInformation* info) {
+  return GetStringFromObjectMethod<IDeviceInformation,
+                                   &IDeviceInformation::get_Name>(info);
+}
+
+HRESULT GetPointerToBufferData(IBuffer* buffer, uint8_t** out) {
+  ScopedComPtr<Windows::Storage::Streams::IBufferByteAccess> buffer_byte_access;
+
+  HRESULT hr = buffer_byte_access.QueryFrom(buffer);
+  if (FAILED(hr)) {
+    VLOG(1) << "QueryInterface failed: " << PrintHr(hr);
+    return hr;
+  }
+
+  // Lifetime of the pointing buffer is controlled by the buffer object.
+  hr = buffer_byte_access->Buffer(out);
+  if (FAILED(hr)) {
+    VLOG(1) << "Buffer failed: " << PrintHr(hr);
+    return hr;
+  }
+
+  return S_OK;
+}
+
+// Tokens with value = 0 are considered as invalid (as in <wrl/event.h>).

[Shao-Chuan Lee, 2016/08/30 02:37:48]

grammar

+const int64_t kInvalidTokenValue = 0;
+
+template <typename InterfaceType>
+struct MidiPort {
+  MidiPort() = default;
+
+  uint32_t index;
+  ScopedComPtr<InterfaceType> handle;
+  base::TimeTicks start_time;
+  EventRegistrationToken token_MessageReceived;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(MidiPort);
+};
+
+}  // namespace
+
+template <typename InterfaceType,
+          typename RuntimeType,
+          typename StaticsInterfaceType,
+          base::char16 const* runtime_class_id>
+class MidiManagerWinrt::MidiPortManager {
+ public:
+  // MidiPortManager instances should be constructed on the COM thread.
+  MidiPortManager(MidiManagerWinrt* midi_manager)
+      : midi_manager_(midi_manager),
+        task_runner_(base::ThreadTaskRunnerHandle::Get()) {}
+
+  bool StartWatcher() {
+    DCHECK(thread_checker_.CalledOnValidThread());
+
+    HRESULT hr;
+
+    midi_port_statics_ =
+        WrlStaticsFactory<StaticsInterfaceType, runtime_class_id>();
+    if (!midi_port_statics_)
+      return false;
+
+    HSTRING device_selector = nullptr;
+    hr = midi_port_statics_->GetDeviceSelector(&device_selector);
+    if (FAILED(hr)) {
+      VLOG(1) << "GetDeviceSelector failed: " << PrintHr(hr);
+      return false;
+    }
+
+    auto dev_info_statics = WrlStaticsFactory<
+        IDeviceInformationStatics,
+        RuntimeClass_Windows_Devices_Enumeration_DeviceInformation>();
+    if (!dev_info_statics)
+      return false;
+
+    hr = dev_info_statics->CreateWatcherAqsFilter(device_selector,
+                                                  watcher_.Receive());
+    if (FAILED(hr)) {
+      VLOG(1) << "CreateWatcherAqsFilter failed: " << PrintHr(hr);
+      return false;
+    }
+
+    // Register callbacks to WinRT that post state-modifying jobs back to COM
+    // thread. |weak_ptr| and |task_runner| are captured by lambda callbacks for
+    // posting jobs. Note that WinRT callback arguments should not be passed
+    // outside the callback since the pointers may be unavailable afterwards.
+    base::WeakPtr<MidiPortManager> weak_ptr = GetWeakPtrFromFactory();
+    scoped_refptr<base::SingleThreadTaskRunner> task_runner = task_runner_;
+
+    hr = watcher_->add_Added(
+        WRL::Callback<ITypedEventHandler<DeviceWatcher*, DeviceInformation*>>(
+            [weak_ptr, task_runner](IDeviceWatcher* watcher,
+                                    IDeviceInformation* info) {
+              std::string dev_id = GetIdString(info),
+                          dev_name = GetNameString(info);
+
+              task_runner->PostTask(
+                  FROM_HERE, base::Bind(&MidiPortManager::OnAdded, weak_ptr,
+                                        dev_id, dev_name));
+
+              return S_OK;
+            })
+            .Get(),
+        &token_Added_);
+    if (FAILED(hr)) {
+      VLOG(1) << "add_Added failed: " << PrintHr(hr);
+      return false;
+    }
+
+    hr = watcher_->add_EnumerationCompleted(
+        WRL::Callback<ITypedEventHandler<DeviceWatcher*, IInspectable*>>(
+            [weak_ptr, task_runner](IDeviceWatcher* watcher,
+                                    IInspectable* insp) {
+              task_runner->PostTask(
+                  FROM_HERE,
+                  base::Bind(&MidiPortManager::OnEnumerationCompleted,
+                             weak_ptr));
+
+              return S_OK;
+            })
+            .Get(),
+        &token_EnumerationCompleted_);
+    if (FAILED(hr)) {
+      VLOG(1) << "add_EnumerationCompleted failed: " << PrintHr(hr);
+      return false;
+    }
+
+    hr = watcher_->add_Removed(
+        WRL::Callback<
+            ITypedEventHandler<DeviceWatcher*, DeviceInformationUpdate*>>(
+            [weak_ptr, task_runner](IDeviceWatcher* watcher,
+                                    IDeviceInformationUpdate* update) {
+              std::string dev_id = GetIdString(update);
+
+              task_runner->PostTask(
+                  FROM_HERE,
+                  base::Bind(&MidiPortManager::OnRemoved, weak_ptr, dev_id));
+
+              return S_OK;
+            })
+            .Get(),
+        &token_Removed_);
+    if (FAILED(hr)) {
+      VLOG(1) << "add_Removed failed: " << PrintHr(hr);
+      return false;
+    }
+
+    hr = watcher_->add_Stopped(
+        WRL::Callback<ITypedEventHandler<DeviceWatcher*, IInspectable*>>(
+            [](IDeviceWatcher* watcher, IInspectable* insp) {
+              // Placeholder, does nothing for now.
+              return S_OK;
+            })
+            .Get(),
+        &token_Stopped_);
+    if (FAILED(hr)) {
+      VLOG(1) << "add_Stopped failed: " << PrintHr(hr);
+      return false;
+    }
+
+    hr = watcher_->add_Updated(
+        WRL::Callback<
+            ITypedEventHandler<DeviceWatcher*, DeviceInformationUpdate*>>(
+            [](IDeviceWatcher* watcher, IDeviceInformationUpdate* update) {
+              // TODO(shaochuan): Check for fields to be updated here.
+              return S_OK;
+            })
+            .Get(),
+        &token_Updated_);
+    if (FAILED(hr)) {
+      VLOG(1) << "add_Updated failed: " << PrintHr(hr);
+      return false;
+    }
+
+    hr = watcher_->Start();
+    if (FAILED(hr)) {
+      VLOG(1) << "Start failed: " << PrintHr(hr);
+      return false;
+    }
+
+    is_initialized_ = true;
+    return true;
+  }
+
+  void StopWatcher() {
+    DCHECK(thread_checker_.CalledOnValidThread());
+
+    HRESULT hr;
+
+    if (token_Added_.value != kInvalidTokenValue) {
+      hr = watcher_->remove_Added(token_Added_);
+      VLOG_IF(1, FAILED(hr)) << "remove_Added failed: " << PrintHr(hr);
+      token_Added_.value = kInvalidTokenValue;
+    }
+    if (token_EnumerationCompleted_.value != kInvalidTokenValue) {
+      hr = watcher_->remove_EnumerationCompleted(token_EnumerationCompleted_);
+      VLOG_IF(1, FAILED(hr)) << "remove_EnumerationCompleted failed: "
+                             << PrintHr(hr);
+      token_EnumerationCompleted_.value = kInvalidTokenValue;
+    }
+    if (token_Removed_.value != kInvalidTokenValue) {
+      hr = watcher_->remove_Removed(token_Removed_);
+      VLOG_IF(1, FAILED(hr)) << "remove_Removed failed: " << PrintHr(hr);
+      token_Removed_.value = kInvalidTokenValue;
+    }
+    if (token_Stopped_.value != kInvalidTokenValue) {
+      hr = watcher_->remove_Stopped(token_Stopped_);
+      VLOG_IF(1, FAILED(hr)) << "remove_Stopped failed: " << PrintHr(hr);
+      token_Stopped_.value = kInvalidTokenValue;
+    }
+    if (token_Updated_.value != kInvalidTokenValue) {
+      hr = watcher_->remove_Updated(token_Updated_);
+      VLOG_IF(1, FAILED(hr)) << "remove_Updated failed: " << PrintHr(hr);
+      token_Updated_.value = kInvalidTokenValue;
+    }
+
+    if (is_initialized_) {
+      hr = watcher_->Stop();
+      VLOG_IF(1, FAILED(hr)) << "Stop failed: " << PrintHr(hr);
+      is_initialized_ = false;
+    }
+  }
+
+  ~MidiPortManager() {
+    DCHECK(thread_checker_.CalledOnValidThread());
+
+    StopWatcher();
+  }
+
+  MidiPort<InterfaceType>* GetPortByDeviceId(std::string dev_id) {
+    DCHECK(thread_checker_.CalledOnValidThread());
+    CHECK(is_initialized_);
+
+    auto it = ports_.find(dev_id);
+    if (it == ports_.end())
+      return nullptr;
+    return it->second.get();
+  }
+
+  MidiPort<InterfaceType>* GetPortByIndex(uint32_t port_index) {
+    DCHECK(thread_checker_.CalledOnValidThread());
+    CHECK(is_initialized_);
+
+    return GetPortByDeviceId(port_ids_[port_index]);
+  }
+
+ protected:
+  // Points to the MidiManagerWinrt instance, which is expected to outlive the
+  // MidiPortManager instance.
+  MidiManagerWinrt* midi_manager_;
+
+  // Task runner of the COM thread.
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+
+  // Ensures all methods are called on the COM thread.
+  base::ThreadChecker thread_checker_;
+
+  // All manipulations to these fields should be done on COM thread.
+  std::unordered_map<std::string, std::unique_ptr<MidiPort<InterfaceType>>>
+      ports_;
+  std::vector<std::string> port_ids_;
+  std::unordered_map<std::string, std::string> port_names_;
+
+  // Set if the instance is initialized without error. Should be checked in all
+  // methods on COM thread except StartWatcher().
+  bool is_initialized_ = false;
+
+ private:
+  // DeviceWatcher callbacks:
+  void OnAdded(std::string dev_id, std::string dev_name) {
+    DCHECK(thread_checker_.CalledOnValidThread());
+    CHECK(is_initialized_);
+
+    // TODO(shaochuan): Disable Microsoft GS Wavetable Synth due to security
+    // reasons. http://crbug.com/499279
+
+    port_names_[dev_id] = dev_name;
+
+    WRL::Wrappers::HString dev_id_hstring;
+    HRESULT hr = dev_id_hstring.Set(base::UTF8ToWide(dev_id).c_str());
+    if (FAILED(hr)) {
+      VLOG(1) << "Set failed: " << PrintHr(hr);
+      return;
+    }
+
+    IAsyncOperation<RuntimeType*>* async_op;
+
+    hr = midi_port_statics_->FromIdAsync(dev_id_hstring.Get(), &async_op);
+    if (FAILED(hr)) {
+      VLOG(1) << "FromIdAsync failed: " << PrintHr(hr);
+      return;
+    }
+
+    base::WeakPtr<MidiPortManager> weak_ptr = GetWeakPtrFromFactory();
+    scoped_refptr<base::SingleThreadTaskRunner> task_runner = task_runner_;
+
+    hr = async_op->put_Completed(
+        WRL::Callback<IAsyncOperationCompletedHandler<RuntimeType*>>(
+            [weak_ptr, task_runner](IAsyncOperation<RuntimeType*>* async_op,
+                                    AsyncStatus status) {
+              // TODO(shaochuan): Check if port open time is accurate.
+              const auto now = base::TimeTicks::Now();
+
+              InterfaceType* handle;
+              HRESULT hr = async_op->GetResults(&handle);
+              if (FAILED(hr)) {
+                VLOG(1) << "GetResults failed: " << PrintHr(hr);
+                return hr;
+              }
+
+              // A reference to |async_op| is kept in |async_ops_|, safe to pass
+              // outside.
+              task_runner->PostTask(
+                  FROM_HERE,
+                  base::Bind(&MidiPortManager::OnCompletedGetPortFromIdAsync,
+                             weak_ptr, handle, now, async_op));
+
+              return S_OK;
+            })
+            .Get());
+    if (FAILED(hr)) {
+      VLOG(1) << "put_Completed failed: " << PrintHr(hr);
+      return;
+    }
+
+    // Keep a reference to incompleted |async_op| for releasing later.
+    async_ops_.insert(async_op);
+  }
+
+  void OnEnumerationCompleted() {
+    DCHECK(thread_checker_.CalledOnValidThread());
+    CHECK(is_initialized_);
+
+    if (async_ops_.empty())
+      midi_manager_->OnPortManagerReady();
+    else
+      enumeration_completed_not_ready_ = true;
+  }
+
+  void OnRemoved(std::string dev_id) {
+    DCHECK(thread_checker_.CalledOnValidThread());
+    CHECK(is_initialized_);
+
+    MidiPort<InterfaceType>* port = GetPortByDeviceId(dev_id);
+    if (!port) {
+      VLOG(1) << "Removing non-existent port " << dev_id;
+      return;
+    }
+
+    SetPortState(port->index, MIDI_PORT_DISCONNECTED);
+
+    RemovePortEventHandlers(port);
+    port->handle = nullptr;
+  }
+
+  void OnCompletedGetPortFromIdAsync(InterfaceType* handle,
+                                     base::TimeTicks start_time,
+                                     IAsyncOperation<RuntimeType*>* async_op) {
+    DCHECK(thread_checker_.CalledOnValidThread());
+    CHECK(is_initialized_);
+
+    EventRegistrationToken token = {kInvalidTokenValue};
+    if (!RegisterOnMessageReceived(handle, &token))
+      return;
+
+    std::string dev_id = GetDeviceIdString(handle);
+
+    MidiPort<InterfaceType>* port = GetPortByDeviceId(dev_id);
+
+    if (port == nullptr) {
+      // TODO(shaochuan): Fill in manufacturer and driver version.
+      AddPort(MidiPortInfo(dev_id, std::string("Manufacturer"),
+                           port_names_[dev_id], std::string("DriverVersion"),
+                           MIDI_PORT_OPENED));
+
+      port = new MidiPort<InterfaceType>;
+      port->index = static_cast<uint32_t>(port_ids_.size());
+
+      ports_[dev_id].reset(port);
+      port_ids_.push_back(dev_id);
+    } else {
+      SetPortState(port->index, MIDI_PORT_CONNECTED);
+    }
+
+    port->handle = handle;
+    port->start_time = start_time;
+    port->token_MessageReceived = token;
+
+    // Manually release COM interface to completed |async_op|.
+    auto it = async_ops_.find(async_op);
+    CHECK(it != async_ops_.end());
+    (*it)->Release();
+    async_ops_.erase(it);
+
+    if (enumeration_completed_not_ready_ && async_ops_.empty()) {
+      midi_manager_->OnPortManagerReady();
+      enumeration_completed_not_ready_ = false;
+    }
+  }
+
+  // Overrided by MidiInPortManager to listen to input ports.
+  virtual bool RegisterOnMessageReceived(InterfaceType* handle,
+                                         EventRegistrationToken* p_token) {
+    return true;
+  }
+
+  // Overrided by MidiInPortManager to remove MessageReceived event handler.
+  virtual void RemovePortEventHandlers(MidiPort<InterfaceType>* port) {}
+
+  // Calls midi_manager_->Add{Input,Output}Port.
+  virtual void AddPort(MidiPortInfo info) = 0;
+
+  // Calls midi_manager_->Set{Input,Output}PortState.
+  virtual void SetPortState(uint32_t port_index, MidiPortState state) = 0;
+
+  // WeakPtrFactory has to be declared in derived class, use this method to
+  // retrieve upcasted WeakPtr for posting tasks.
+  virtual base::WeakPtr<MidiPortManager> GetWeakPtrFromFactory() = 0;
+
+  // Midi{In,Out}PortStatics instance.
+  ScopedComPtr<StaticsInterfaceType> midi_port_statics_;
+
+  // DeviceWatcher instance and event registration tokens for unsubscribing
+  // events in destructor.
+  ScopedComPtr<IDeviceWatcher> watcher_;
+  EventRegistrationToken token_Added_ = {kInvalidTokenValue},
+                         token_EnumerationCompleted_ = {kInvalidTokenValue},
+                         token_Removed_ = {kInvalidTokenValue},
+                         token_Stopped_ = {kInvalidTokenValue},
+                         token_Updated_ = {kInvalidTokenValue};
+
+  // Keeps AsyncOperation references before the operation completes. Note that
+  // raw pointers are used here and the COM interfaces should be released
+  // manually.
+  std::unordered_set<IAsyncOperation<RuntimeType*>*> async_ops_;
+
+  // Set when device enumeration is completed but OnPortManagerReady() is not
+  // called since some ports are not yet ready (i.e. |async_ops_| is not empty).
+  // In such cases, OnPortManagerReady() will be called in
+  // OnCompletedGetPortFromIdAsync() when the last pending port is ready.
+  bool enumeration_completed_not_ready_ = false;
+};
+
+class MidiManagerWinrt::MidiInPortManager final
+    : public MidiPortManager<IMidiInPort,
+                             MidiInPort,
+                             IMidiInPortStatics,
+                             RuntimeClass_Windows_Devices_Midi_MidiInPort> {
+ public:
+  MidiInPortManager(MidiManagerWinrt* midi_manager)
+      : MidiPortManager(midi_manager), weak_factory_(this) {}
+
+  ~MidiInPortManager() {
+    DCHECK(thread_checker_.CalledOnValidThread());
+    if (!is_initialized_)
+      return;
+
+    for (const auto& entry : ports_)
+      RemovePortEventHandlers(entry.second.get());
+  }
+
+ private:
+  // MidiPortManager overrides:
+  bool RegisterOnMessageReceived(IMidiInPort* handle,
+                                 EventRegistrationToken* p_token) override {
+    DCHECK(thread_checker_.CalledOnValidThread());
+
+    base::WeakPtr<MidiInPortManager> weak_ptr = weak_factory_.GetWeakPtr();
+    scoped_refptr<base::SingleThreadTaskRunner> task_runner = task_runner_;
+
+    HRESULT hr = handle->add_MessageReceived(
+        WRL::Callback<
+            ITypedEventHandler<MidiInPort*, MidiMessageReceivedEventArgs*>>(
+            [weak_ptr, task_runner](IMidiInPort* handle,
+                                    IMidiMessageReceivedEventArgs* args) {
+              std::string dev_id = GetDeviceIdString(handle);
+
+              ScopedComPtr<IMidiMessage> message;
+              HRESULT hr = args->get_Message(message.Receive());
+              if (FAILED(hr)) {
+                VLOG(1) << "get_Message failed: " << PrintHr(hr);
+                return hr;
+              }
+
+              ScopedComPtr<IBuffer> buffer;
+              hr = message->get_RawData(buffer.Receive());
+              if (FAILED(hr)) {
+                VLOG(1) << "get_RawData failed: " << PrintHr(hr);
+                return hr;
+              }
+
+              uint8_t* p_buffer_data = nullptr;
+              hr = GetPointerToBufferData(buffer.get(), &p_buffer_data);
+              if (FAILED(hr))
+                return hr;
+
+              uint32_t data_length = 0;
+              hr = buffer->get_Length(&data_length);
+              if (FAILED(hr)) {
+                VLOG(1) << "get_Length failed: " << PrintHr(hr);
+                return hr;
+              }
+
+              std::vector<uint8_t> data(p_buffer_data,
+                                        p_buffer_data + data_length);
+
+              // Time since port opened in 100-nanosecond units.
+              TimeSpan time_span;
+              hr = message->get_Timestamp(&time_span);
+              if (FAILED(hr)) {
+                VLOG(1) << "get_Timestamp failed: " << PrintHr(hr);
+                return hr;
+              }
+
+              task_runner->PostTask(
+                  FROM_HERE,
+                  base::Bind(&MidiInPortManager::OnMessageReceived, weak_ptr,
+                             dev_id, data, base::TimeDelta::FromMicroseconds(
+                                               time_span.Duration / 10)));
+
+              return S_OK;
+            })
+            .Get(),
+        p_token);
+    if (FAILED(hr)) {
+      VLOG(1) << "add_MessageReceived failed: " << PrintHr(hr);
+      return false;
+    }
+
+    return true;
+  }
+
+  void RemovePortEventHandlers(MidiPort<IMidiInPort>* port) {
+    if (!(port->handle &&
+          port->token_MessageReceived.value != kInvalidTokenValue))
+      return;
+
+    HRESULT hr =
+        port->handle->remove_MessageReceived(port->token_MessageReceived);
+    VLOG_IF(1, FAILED(hr)) << "remove_MessageReceived failed: " << PrintHr(hr);
+  }
+
+  void AddPort(MidiPortInfo info) final { midi_manager_->AddInputPort(info); }
+
+  void SetPortState(uint32_t port_index, MidiPortState state) final {
+    midi_manager_->SetInputPortState(port_index, state);
+  }
+
+  base::WeakPtr<MidiPortManager> GetWeakPtrFromFactory() final {
+    DCHECK(thread_checker_.CalledOnValidThread());
+
+    return weak_factory_.GetWeakPtr();
+  }
+
+  // Callback on receiving MIDI input message.
+  void OnMessageReceived(std::string dev_id,
+                         std::vector<uint8_t> data,
+                         base::TimeDelta time_since_start) {
+    DCHECK(thread_checker_.CalledOnValidThread());
+
+    MidiPort<IMidiInPort>* port = GetPortByDeviceId(dev_id);
+    CHECK(port);
+
+    midi_manager_->ReceiveMidiData(port->index, &data[0], data.size(),
+                                   port->start_time + time_since_start);
+  }
+
+  // Last member to ensure destructed first.
+  base::WeakPtrFactory<MidiInPortManager> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(MidiInPortManager);
+};
+
+class MidiManagerWinrt::MidiOutPortManager final
+    : public MidiPortManager<IMidiOutPort,
+                             IMidiOutPort,
+                             IMidiOutPortStatics,
+                             RuntimeClass_Windows_Devices_Midi_MidiOutPort> {
+ public:
+  MidiOutPortManager(MidiManagerWinrt* midi_manager)
+      : MidiPortManager(midi_manager), weak_factory_(this) {}
+
+ private:
+  // MidiPortManager overrides:
+  void AddPort(MidiPortInfo info) final { midi_manager_->AddOutputPort(info); }
+
+  void SetPortState(uint32_t port_index, MidiPortState state) final {
+    midi_manager_->SetOutputPortState(port_index, state);
+  }
+
+  base::WeakPtr<MidiPortManager> GetWeakPtrFromFactory() final {
+    DCHECK(thread_checker_.CalledOnValidThread());
+
+    return weak_factory_.GetWeakPtr();
+  }
+
+  // Last member to ensure destructed first.
+  base::WeakPtrFactory<MidiOutPortManager> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(MidiOutPortManager);
+};
+
+MidiManagerWinrt::MidiManagerWinrt() : com_thread_("Windows MIDI COM Thread") {}
+
+MidiManagerWinrt::~MidiManagerWinrt() {
+  base::AutoLock auto_lock(lazy_init_member_lock_);
+
+  CHECK(!com_thread_checker_);
+  CHECK(!port_manager_in_);
+  CHECK(!port_manager_out_);
+  CHECK(!scheduler_);
+}
+
+void MidiManagerWinrt::StartInitialization() {
+  if (base::win::GetVersion() < base::win::VERSION_WIN10) {
+    VLOG(1) << "WinRT MIDI backend is only supported on Windows 10 or later.";
+    CompleteInitialization(Result::INITIALIZATION_ERROR);
+    return;
+  }
+
+  com_thread_.init_com_with_mta(true);
+  com_thread_.Start();
+
+  com_thread_.task_runner()->PostTask(
+      FROM_HERE, base::Bind(&MidiManagerWinrt::InitializeOnComThread,
+                            base::Unretained(this)));
+}
+
+void MidiManagerWinrt::Finalize() {
+  com_thread_.task_runner()->PostTask(
+      FROM_HERE, base::Bind(&MidiManagerWinrt::FinalizeOnComThread,
+                            base::Unretained(this)));
+
+  // Blocks until FinalizeOnComThread() returns. Delayed MIDI send data tasks
+  // will be ignored.
+  com_thread_.Stop();
+}
+
+void MidiManagerWinrt::DispatchSendMidiData(MidiManagerClient* client,
+                                            uint32_t port_index,
+                                            const std::vector<uint8_t>& data,
+                                            double timestamp) {
+  CHECK(scheduler_);
+
+  scheduler_->PostSendDataTask(
+      client, data.size(), timestamp,
+      base::Bind(&MidiManagerWinrt::SendOnComThread, base::Unretained(this),
+                 port_index, data));
+}
+
+void MidiManagerWinrt::InitializeOnComThread() {
+  base::AutoLock auto_lock(lazy_init_member_lock_);
+
+  com_thread_checker_.reset(new base::ThreadChecker);
+
+  port_manager_in_.reset(new MidiInPortManager(this));
+  port_manager_out_.reset(new MidiOutPortManager(this));
+
+  scheduler_.reset(new MidiScheduler(this));
+
+  if (!(port_manager_in_->StartWatcher() &&
+        port_manager_out_->StartWatcher())) {
+    CompleteInitialization(Result::INITIALIZATION_ERROR);

[Takashi Toyoshima, 2016/08/29 16:20:17]

It's natural and probably safe to call CompleteInitialization after calling
StopWatcher()s.

[Shao-Chuan Lee, 2016/08/30 02:37:48]

Done. This was actually a copy/paste mistake..

+    port_manager_in_->StopWatcher();
+    port_manager_out_->StopWatcher();
+  }
+}
+
+void MidiManagerWinrt::FinalizeOnComThread() {
+  base::AutoLock auto_lock(lazy_init_member_lock_);
+
+  DCHECK(com_thread_checker_->CalledOnValidThread());
+
+  scheduler_.reset();
+
+  port_manager_in_.reset();
+  port_manager_out_.reset();
+
+  com_thread_checker_.reset();
+}
+
+void MidiManagerWinrt::SendOnComThread(uint32_t port_index,
+                                       const std::vector<uint8_t>& data) {
+  DCHECK(com_thread_checker_->CalledOnValidThread());
+
+  MidiPort<IMidiOutPort>* port = port_manager_out_->GetPortByIndex(port_index);
+  if (!(port && port->handle)) {
+    VLOG(1) << "Port not available: " << port_index;
+    return;
+  }
+
+  auto buffer_factory =
+      WrlStaticsFactory<IBufferFactory,
+                        RuntimeClass_Windows_Storage_Streams_Buffer>();
+  if (!buffer_factory)
+    return;
+
+  ScopedComPtr<IBuffer> buffer;
+  HRESULT hr = buffer_factory->Create(static_cast<UINT32>(data.size()),
+                                      buffer.Receive());
+  if (FAILED(hr)) {
+    VLOG(1) << "Create failed: " << PrintHr(hr);
+    return;
+  }
+
+  hr = buffer->put_Length(static_cast<UINT32>(data.size()));
+  if (FAILED(hr)) {
+    VLOG(1) << "put_Length failed: " << PrintHr(hr);
+    return;
+  }
+
+  uint8_t* p_buffer_data = nullptr;
+  hr = GetPointerToBufferData(buffer.get(), &p_buffer_data);
+  if (FAILED(hr))
+    return;
+
+  std::copy(data.begin(), data.end(), p_buffer_data);
+
+  hr = port->handle->SendBuffer(buffer.get());
+  if (FAILED(hr)) {
+    VLOG(1) << "SendBuffer failed: " << PrintHr(hr);
+    return;
+  }
+}
+
+void MidiManagerWinrt::OnPortManagerReady() {
+  DCHECK(com_thread_checker_->CalledOnValidThread());
+  DCHECK(port_manager_ready_count_ < 2);
+
+  if (++port_manager_ready_count_ == 2)
+    CompleteInitialization(Result::OK);
+}
+
+MidiManager* MidiManager::Create() {
+  return new MidiManagerWinrt();
+}
+
+}  // namespace midi
+}  // namespace media