Enable WebMIDI for Windows behind the flag

media/midi/midi_manager_win.cc

+// Copyright (c) 2013 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_win.h"
+
+#include <Windows.h>

[scherkus (not reviewing), 2013/11/27 22:07:30]

Windows -> windows

[yukawa, 2013/12/04 17:51:22]

Done.

+
+// Prevent unnecessary functions from being included from <mmsystem.h>
+#define MMNODRV
+#define MMNOSOUND
+#define MMNOWAVE
+#define MMNOAUX
+#define MMNOMIXER
+#define MMNOTIMER
+#define MMNOJOY
+#define MMNOMCI
+#define MMNOMMIO
+#include <mmsystem.h>
+
+#include "base/bind.h"
+#include "base/message_loop/message_loop.h"
+#include "base/strings/string_number_conversions.h"
+#include "base/strings/utf_string_conversions.h"
+#include "base/threading/thread.h"
+#include "media/midi/midi_message_queue.h"
+#include "media/midi/midi_message_util.h"
+#include "media/midi/midi_port_info.h"
+
+namespace media {
+namespace {
+
+std::string GetInErrorMessage(MMRESULT result) {
+  wchar_t text[MAXERRORLENGTH];
+  MMRESULT get_result = midiInGetErrorText(result, text, arraysize(text));
+  if (get_result != MMSYSERR_NOERROR) {
+    DLOG(ERROR) << "Failed to get error message."
+                << " original error: " << result
+                << " midiInGetErrorText error: " << get_result;
+    return std::string();
+  }
+  return WideToUTF8(text);
+}
+
+std::string GetOutErrorMessage(MMRESULT result) {
+  wchar_t text[MAXERRORLENGTH];
+  MMRESULT get_result = midiOutGetErrorText(result, text, arraysize(text));
+  if (get_result != MMSYSERR_NOERROR) {
+    DLOG(ERROR) << "Failed to get error message."
+                << " original error: " << result
+                << " midiOutGetErrorText error: " << get_result;
+    return std::string();
+  }
+  return WideToUTF8(text);
+}
+
+class MIDIHDRDeleter {
+ public:
+  void operator()(MIDIHDR* header) {
+    if (!header)
+      return;
+    delete[] static_cast<char*>(header->lpData);
+    header->lpData = NULL;
+    header->dwBufferLength = 0;
+    delete header;
+  }
+};
+
+typedef scoped_ptr<MIDIHDR, MIDIHDRDeleter> ScopedMIDIHDR;
+
+ScopedMIDIHDR CreateMIDIHDR(size_t size) {
+  ScopedMIDIHDR header(new MIDIHDR);
+  ZeroMemory(header.get(), sizeof(*header));
+  header->lpData = new char[size];
+  header->dwBufferLength = size;
+  return header.Pass();
+}
+
+void SendShortMIDIMessageInternal(HMIDIOUT midi_out_handle,
+                                  const std::vector<uint8>& message) {
+  if (message.size() >= 4)
+    return;
+
+  DWORD packed_message = 0;
+  for (size_t i = 0; i < message.size(); ++i)
+    packed_message |= (static_cast<uint32>(message[i]) << (i * 8));
+  MMRESULT result = midiOutShortMsg(midi_out_handle, packed_message);
+  DLOG_IF(ERROR, result != MMSYSERR_NOERROR)
+      << "Failed to output short message: " << GetOutErrorMessage(result);
+}
+
+void SendLongMIDIMessageInternal(HMIDIOUT midi_out_handle,
+                                 const std::vector<uint8>& message) {
+  // Implementation note:
+  // Sending long MIDI message can be performed synchronously or asynchronously
+  // depending on the driver. There are 2 options to support both cases:
+  // 1) Call midiOutLongMsg API and wait for its completion within this

[scherkus (not reviewing), 2013/11/27 22:07:30]

nit: can you annotate function calls in comments with ()?

e.g., midiOutLongMsg()

it's a bit of a commenting convention we have to make it easier to distinguish
method names in comments from classes and types

[yukawa, 2013/12/04 17:51:22]

Done.

+  //   function. In this approach, we can avoid memory copy by directly pointing
+  //   |message| as the data buffer to be sent.
+  // 2) Allocate a buffer and copy |message| to it, then call midiOutLongMsg

[scherkus (not reviewing), 2013/11/27 22:07:30]

ditto here + on line 102

[yukawa, 2013/12/04 17:51:22]

Done.

+  //   API. The buffer will be freed in the MOM_DONE event hander, which tells
+  //   us that the task of midiOutLongMsg API is completed.
+  // Here we use option 2) in favor of asynchronous design.
+  //
+  // Open question:
+  // In the era of USB-MIDI, OS built-in driver seems to always perform
+  // synchronously. Thus option 1) still might be a good option.

[scherkus (not reviewing), 2013/11/27 22:07:30]

how long are these synchronous operations?

as you note, we can wedge the UI thread on shutdown while waiting for this task
to complete + send_thread_ to stop

[yukawa, 2013/12/04 17:51:22]

On my Windows environment with a certain USB-MIDI keyboard, the transfer rate is
roughly 75 KByte/sec at plateau region. Thus it can take very long time unless
we put some size limit.

I tentatively put 60 KB size limit so that the API is blocked at most 1 sec or
so. I also introduced a |quitting_| flag to prevent pending messages from being
passed to APIs. Now my guts feeling is that |send_thread_.Stop()| takes roughly
1 sec in the worst case, which sounds to be an acceptable duration to me.
What do you think?

+
+  ScopedMIDIHDR midi_header(CreateMIDIHDR(message.size()));
+  for (size_t i = 0; i < message.size(); ++i)
+    midi_header->lpData[i] = static_cast<char>(message[i]);
+
+  MMRESULT result = midiOutPrepareHeader(
+      midi_out_handle, midi_header.get(), sizeof(*midi_header));
+  if (result != MMSYSERR_NOERROR) {
+    DLOG(ERROR) << "Failed to prepare output buffer: "
+                << GetOutErrorMessage(result);
+    return;
+  }
+
+  result = midiOutLongMsg(
+      midi_out_handle, midi_header.get(), sizeof(*midi_header));
+  if (result != MMSYSERR_NOERROR) {
+    DLOG(ERROR) << "Failed to output long message: "
+                << GetOutErrorMessage(result);
+    result = midiOutUnprepareHeader(
+        midi_out_handle, midi_header.get(), sizeof(*midi_header));
+    DLOG_IF(ERROR, result != MMSYSERR_NOERROR)
+        << "Failed to uninitialize output buffer: "
+        << GetOutErrorMessage(result);
+    return;
+  }
+
+  // The ownership of |midi_header| is moved to MOM_DONE event handler.
+  midi_header.release();
+}
+
+void SendMIDIDataInternal(HMIDIOUT midi_out_handle,
+                          const std::vector<uint8>& data) {
+  // MIDI Running status must not be enabled for |data|.
+  MIDIMessageQueue message_queue(false);
+  message_queue.Add(data);
+  std::vector<uint8> message;
+  while (true) {
+    message_queue.Get(&message);
+    if (message.empty())
+      break;
+    // SendShortMIDIMessageInternal can send a MIDI message up to 3 bytes.
+    if (message.size() <= 3)
+      SendShortMIDIMessageInternal(midi_out_handle, message);
+    else
+      SendLongMIDIMessageInternal(midi_out_handle, message);
+  }
+}
+
+}  // namespace
+
+class MIDIManagerWin::InPortInfo {
+ public:
+  ~InPortInfo() {
+    Uninitialize();
+  }
+  void set_port_index(int index) {
+    port_index_ = index;
+  }
+  int port_index() const {
+    return port_index_;
+  }
+  bool device_to_be_closed() const {
+    return device_to_be_closed_;
+  }
+  HMIDIIN midi_handle() const {
+    return midi_handle_;
+  }
+  const base::TimeDelta& start_time_offset() const {
+    return start_time_offset_;
+  }
+
+  static scoped_ptr<InPortInfo> Create(MIDIManagerWin* manager,
+                                       UINT device_id) {
+    scoped_ptr<InPortInfo> obj(new InPortInfo(manager));
+    if (!obj->Initialize(device_id))
+      obj.reset(NULL);

[scherkus (not reviewing), 2013/11/27 22:07:30]

nit: no need for null

[yukawa, 2013/12/04 17:51:22]

Done.

+    return obj.Pass();
+  }
+
+ private:
+  static const int kInvalidPortIndex = -1;
+  static const size_t kBufferLength = 32 * 1024;
+
+  explicit InPortInfo(MIDIManagerWin* manager)
+      : manager_(manager),
+        port_index_(kInvalidPortIndex),
+        midi_handle_(NULL),
+        started_(false),
+        device_to_be_closed_(false) {
+  }
+
+  bool Initialize(DWORD device_id) {
+    Uninitialize();
+    midi_header_ = CreateMIDIHDR(kBufferLength);
+
+    // Here we use |CALLBACK_FUNCTION| to subscribe MIM_DATA, MIM_LONGDATA, and
+    // MIM_CLOSE events.
+    // - MIM_DATA: This is the only way to get a short MIDI message with
+    //     timestamp information.
+    // - MIM_LONGDATA: This is the only way to get a long MIDI message with
+    //     timestamp information.
+    // - MIN_CLOSE: This event is notified when the device is removed logically
+    //     or physically.
+    MMRESULT result = midiInOpen(&midi_handle_,
+                                 device_id,
+                                 reinterpret_cast<DWORD_PTR>(&HandleMessage),
+                                 reinterpret_cast<DWORD_PTR>(this),
+                                 CALLBACK_FUNCTION);
+    if (result != MMSYSERR_NOERROR) {
+      DLOG(ERROR) << "Failed to open output device. "
+                  << " id: " << device_id
+                  << " message: " << GetInErrorMessage(result);
+      return false;
+    }
+    result = midiInPrepareHeader(
+        midi_handle_, midi_header_.get(), sizeof(*midi_header_));
+    if (result != MMSYSERR_NOERROR) {
+      DLOG(ERROR) << "Failed to initialize input buffer: "
+                  << GetInErrorMessage(result);
+      return false;
+    }
+    result = midiInAddBuffer(
+        midi_handle_, midi_header_.get(), sizeof(*midi_header_));
+    if (result != MMSYSERR_NOERROR) {
+      DLOG(ERROR) << "Failed to attach input buffer: "
+                  << GetInErrorMessage(result);
+      return false;
+    }
+    result = midiInStart(midi_handle_);
+    if (result != MMSYSERR_NOERROR) {
+      DLOG(ERROR) << "Failed to start input port: "
+                  << GetInErrorMessage(result);
+      return false;
+    }
+    started_ = true;
+    start_time_offset_ = base::TimeTicks::Now() - base::TimeTicks();
+    return true;
+  }
+
+  void Uninitialize() {
+    MMRESULT result = MMSYSERR_NOERROR;
+    if (midi_handle_ && started_) {
+      result = midiInStop(midi_handle_);
+      DLOG_IF(ERROR, result != MMSYSERR_NOERROR)
+          << "Failed to stop input port: " << GetInErrorMessage(result);
+      started_ = false;
+      start_time_offset_ = base::TimeDelta();
+    }
+    if (midi_handle_) {
+      // midiInReset flushes pending messages. We ignore these messages.
+      device_to_be_closed_ = true;
+      result = midiInReset(midi_handle_);
+      DLOG_IF(ERROR, result != MMSYSERR_NOERROR)
+          << "Failed to reset input port: " << GetInErrorMessage(result);
+      result = midiInClose(midi_handle_);
+      DLOG_IF(ERROR, result != MMSYSERR_NOERROR)
+          << "Failed to close input port: " << GetInErrorMessage(result);
+    }
+    device_to_be_closed_ = false;
+  }
+
+  static void CALLBACK HandleMessage(HMIDIIN midi_in_handle,
+                                     UINT message,
+                                     DWORD_PTR instance,
+                                     DWORD_PTR param1,
+                                     DWORD_PTR param2) {
+    // This method is called back by Windows multimedia subsystem and not always
+    // in the UI thread.
+    InPortInfo* self = reinterpret_cast<InPortInfo*>(instance);
+    if (!self)
+      return;
+    if (self->midi_handle() != midi_in_handle)
+      return;
+    self->HandleMessageInternal(message, param1, param2);
+  }
+
+  void HandleMessageInternal(UINT message, DWORD_PTR param1, DWORD_PTR param2) {
+    // This method is called from HandleMessage method and not always in the UI
+    // thread.
+    switch (message) {
+      case MIM_DATA:
+        HandleShortMessageInternal(static_cast<uint8>(param1 & 0xff),
+                                   static_cast<uint8>((param1 >> 8) & 0xff),
+                                   static_cast<uint8>((param1 >> 16) & 0xff),
+                                   TickToTimeDelta(param2));
+        return;
+      case MIM_LONGDATA:
+        HandleLongMessageInternal(reinterpret_cast<MIDIHDR*>(param1),
+                                  TickToTimeDelta(param2));
+        return;
+      case MIM_CLOSE:
+        HandleCloseMessageInternal();
+    }
+  }
+
+  void HandleShortMessageInternal(uint8 status_byte,
+                                  uint8 first_data_byte,
+                                  uint8 second_data_byte,
+                                  base::TimeDelta timestamp) {
+    if (device_to_be_closed())
+      return;
+    const size_t len = GetMIDIMessageLength(status_byte);
+    if (len == 0 || port_index() == kInvalidPortIndex)
+      return;
+    const uint8 kData[] = { status_byte, first_data_byte, second_data_byte };
+    DCHECK_LE(len, arraysize(kData));
+    manager_->ReceiveMIDIData(port_index(), kData, len, timestamp.InSecondsF());
+  }
+
+  void HandleLongMessageInternal(MIDIHDR* header, base::TimeDelta timestamp) {
+    if (header != midi_header_.get())
+      return;
+    MMRESULT result = MMSYSERR_NOERROR;
+    if (device_to_be_closed()) {
+      if (midi_header_ &&
+          (midi_header_->dwFlags & MHDR_PREPARED) == MHDR_PREPARED) {
+        result = midiInUnprepareHeader(
+          midi_handle_, midi_header_.get(), sizeof(*midi_header_));
+        DLOG_IF(ERROR, result != MMSYSERR_NOERROR)
+            << "Failed to uninitialize input buffer: "
+            << GetInErrorMessage(result);
+      }
+      return;
+    }
+    if (header->dwBytesRecorded > 0 && port_index() != kInvalidPortIndex) {
+      manager_->ReceiveMIDIData(port_index_,
+                                reinterpret_cast<const uint8*>(header->lpData),
+                                header->dwBytesRecorded,
+                                timestamp.InSecondsF());
+    }
+    result = midiInAddBuffer(midi_handle(), header, sizeof(*header));
+    DLOG_IF(ERROR, result != MMSYSERR_NOERROR)
+        << "Failed to attach input port: " << GetInErrorMessage(result);
+  }
+
+  void HandleCloseMessageInternal() {
+    if (midi_handle_ && midi_header_ &&
+        (midi_header_->dwFlags & MHDR_PREPARED) == MHDR_PREPARED) {
+      MMRESULT result = midiInUnprepareHeader(
+          midi_handle_, midi_header_.get(), sizeof(*midi_header_));
+      DLOG_IF(ERROR, result != MMSYSERR_NOERROR)
+          << "Failed to uninitialize input buffer: "
+          << GetInErrorMessage(result);
+    }
+    midi_header_.reset();
+    midi_handle_ = NULL;
+    port_index_ = kInvalidPortIndex;
+    return;
+  }
+
+  base::TimeDelta TickToTimeDelta(DWORD tick) const {
+    const base::TimeDelta delta =
+        base::TimeDelta::FromMicroseconds(static_cast<uint32>(tick));
+    return start_time_offset_ + delta;
+  }
+
+  MIDIManagerWin* manager_;
+  int port_index_;
+  HMIDIIN midi_handle_;
+  ScopedMIDIHDR midi_header_;
+  base::TimeDelta start_time_offset_;
+  bool started_;
+  bool device_to_be_closed_;
+  DISALLOW_COPY_AND_ASSIGN(MIDIManagerWin::InPortInfo);
+};
+
+class MIDIManagerWin::OutPortInfo {
+ public:
+  ~OutPortInfo() {
+    Uninitialize();
+  }
+
+  HMIDIOUT midi_handle() const {
+    return midi_handle_;
+  }
+
+  static scoped_ptr<OutPortInfo> Create(UINT device_id) {
+    scoped_ptr<OutPortInfo> obj(new OutPortInfo);
+    if (!obj->Initialize(device_id))
+      obj.reset(NULL);

[scherkus (not reviewing), 2013/11/27 22:07:30]

nit: no need for NULL

[yukawa, 2013/12/04 17:51:22]

Done.

+    return obj.Pass();
+  }
+
+ private:
+  OutPortInfo()
+      : midi_handle_(NULL) {}
+
+  bool Initialize(DWORD device_id) {
+    Uninitialize();
+    // Here we use |CALLBACK_FUNCTION| to subscribe MOM_DONE and MOM_CLOSE
+    // events.
+    // - MOM_DONE: SendLongMIDIMessageInternal relies on this event to clean up

[scherkus (not reviewing), 2013/11/27 22:07:30]

ditto for function names in comments

[yukawa, 2013/12/04 17:51:22]

Done.

+    //     the backing store where a long MIDI message is stored.
+    // - MOM_CLOSE: This event is notified when the device is removed logically
+    //     or physically.
+    MMRESULT result = midiOutOpen(&midi_handle_,
+                                  device_id,
+                                  reinterpret_cast<DWORD_PTR>(&HandleMessage),
+                                  reinterpret_cast<DWORD_PTR>(this),
+                                  CALLBACK_FUNCTION);
+    if (result != MMSYSERR_NOERROR) {
+      DLOG(ERROR) << "Failed to open output device. "
+                  << " id: " << device_id
+                  << " message: "<< GetOutErrorMessage(result);
+      midi_handle_ = NULL;
+      return false;
+    }
+    return true;
+  }
+
+  void Uninitialize() {
+    if (midi_handle_ == NULL)

[scherkus (not reviewing), 2013/11/27 22:07:30]

nit: use !midi_handle_

[yukawa, 2013/12/04 17:51:22]

Done.

+      return;
+    MMRESULT result = midiOutReset(midi_handle_);
+    DLOG_IF(ERROR, result != MMSYSERR_NOERROR)
+        << "Failed to reset output port: " << GetOutErrorMessage(result);
+    result = midiOutClose(midi_handle_);
+    DLOG_IF(ERROR, result != MMSYSERR_NOERROR)
+        << "Failed to close output port: " << GetOutErrorMessage(result);
+    midi_handle_ = NULL;
+  }
+
+  static void CALLBACK HandleMessage(HMIDIIN midi_in_handle,
+                                     UINT message,
+                                     DWORD_PTR instance,
+                                     DWORD_PTR param1,
+                                     DWORD_PTR param2) {
+    // This method is called back by Windows multimedia subsystem and not always
+    // in the UI thread.

[scherkus (not reviewing), 2013/11/27 22:07:30]

s/in/on/

also what do you mean by "not always"?

do we know when it's called on UI vs. some other thread? if it's not the UI
thread ... which thread is it?

[yukawa, 2013/12/04 17:51:22]

Done and added comment.

+
+    OutPortInfo* self = reinterpret_cast<OutPortInfo*>(instance);
+    if (!self)
+      return;
+    switch (message) {
+      case MOM_DONE: {
+        // Take the ownership of the MIDIHDR object.
+        ScopedMIDIHDR header(reinterpret_cast<MIDIHDR*>(param1));
+        if (!header)
+          return;
+        MMRESULT result = midiOutUnprepareHeader(
+            self->midi_handle(), header.get(), sizeof(*header));
+        DLOG_IF(ERROR, result != MMSYSERR_NOERROR)
+            << "Failed to uninitialize output buffer: "
+            << GetOutErrorMessage(result);
+        return;
+      }
+      case MOM_CLOSE:
+        self->midi_handle_ = NULL;
+        return;
+    }
+  }
+
+  HMIDIOUT midi_handle_;
+  DISALLOW_COPY_AND_ASSIGN(MIDIManagerWin::OutPortInfo);
+};
+
+MIDIManagerWin::MIDIManagerWin() {
+}
+
+bool MIDIManagerWin::Initialize() {
+  {

[scherkus (not reviewing), 2013/11/27 22:07:30]

do we need the extra scope blocks?

I'm not seeing any variables that are declared that would benefit from the extra
level of scope

[yukawa, 2013/12/04 17:51:22]

OK. Removed these blocks.

+    const UINT num_in_devices = midiInGetNumDevs();
+    in_ports_.reserve(num_in_devices);
+    for (UINT device_id = 0; device_id < num_in_devices; ++device_id) {
+      MIDIINCAPS caps = {};
+      MMRESULT result = midiInGetDevCaps(device_id, &caps, sizeof(caps));
+      if (result != MMSYSERR_NOERROR) {
+        DLOG(ERROR) << "Failed to obtain input device info: "
+                    << GetInErrorMessage(result);
+        continue;
+      }
+      scoped_ptr<InPortInfo> in_port(InPortInfo::Create(this, device_id));
+      if (!in_port)
+        continue;
+      MIDIPortInfo info(
+          base::IntToString(static_cast<int>(device_id)),
+          "",
+          base::WideToUTF8(caps.szPname),
+          base::IntToString(static_cast<int>(caps.vDriverVersion)));
+      AddInputPort(info);
+      in_port->set_port_index(input_ports_.size() - 1);
+      in_ports_.push_back(in_port.Pass());
+    }
+  }
+  {
+    const UINT num_out_devices = midiOutGetNumDevs();
+    out_ports_.reserve(num_out_devices);
+    for (UINT device_id = 0; device_id < num_out_devices; ++device_id) {
+      MIDIOUTCAPS caps = {};
+      MMRESULT result = midiOutGetDevCaps(device_id, &caps, sizeof(caps));
+      if (result != MMSYSERR_NOERROR) {
+        DLOG(ERROR) << "Failed to obtain output device info: "
+                    << GetOutErrorMessage(result);
+        continue;
+      }
+      scoped_ptr<OutPortInfo> out_port(OutPortInfo::Create(device_id));
+      if (!out_port)
+        continue;
+      MIDIPortInfo info(
+          base::IntToString(static_cast<int>(device_id)),
+          "",
+          base::WideToUTF8(caps.szPname),
+          base::IntToString(static_cast<int>(caps.vDriverVersion)));
+      AddOutputPort(info);
+      out_ports_.push_back(out_port.Pass());
+    }
+  }
+  return true;
+}
+
+MIDIManagerWin::~MIDIManagerWin() {
+  // |send_thread_| must be terminated here to ensure that
+  // MIDIManagerWin::SendMIDIData will not be called any longer. A drawback

[scherkus (not reviewing), 2013/11/27 22:07:30]

ditto for function names in comments

[yukawa, 2013/12/04 17:51:22]

Done.

+  // of this approach is if |send_thread_| is somehow blocked forever,

[scherkus (not reviewing), 2013/11/27 22:07:30]

do you know how long does it take to run SendMIDIDataInternal()?

is it possible for the OS to block for a long time?

[yukawa, 2013/12/04 17:51:22]

It is supposed to be fast operation as long as there is no pending tasks. In the
worst case scenario, I estimate the upper limit as roughly 1 sec. See above
comment for details.

+  // the UI thread is also blocked forever.
+  send_thread_.reset(NULL);

[scherkus (not reviewing), 2013/11/27 22:07:30]

nit: NULL not needed

[yukawa, 2013/12/04 17:51:22]

Done.

+}
+
+void MIDIManagerWin::SendMIDIData(MIDIManagerClient* client,
+                                  uint32 port_index,
+                                  const std::vector<uint8>& data,
+                                  double timestamp) {
+  DCHECK(CurrentlyOnMIDISendThread());
+  // Caveat: Whether |this| is still valid or not is non-trivial question
+  // because this method is called back in a background thread that is owned by
+  // MIDIManager rather than MIDIManagerWin. Currently |this| is considered to
+  // be always valid because ~MIDIManagerWin() internally waits for the
+  // termination of this background thread.

[scherkus (not reviewing), 2013/11/27 22:07:30]

technically this comment would apply to MIDIManagerMac as well, but I don't see
it resetting send_thread_

are you worried about the PostDelayedTask()?

[yukawa, 2013/12/04 17:51:22]

Mas issue has been resolved. PostDelayedTask() is also fine in the latest patch.

+
+  if (out_ports_.size() <= port_index)
+    return;
+
+  // Check if the target device is still available. Note that |handle| can be
+  // NULL once the device is logically or physically removed.
+  const HMIDIOUT handle = out_ports_[port_index]->midi_handle();
+  if (!handle)
+    return;
+
+  base::TimeDelta delay;
+  if (timestamp != 0.0) {
+    base::TimeTicks time_to_send =
+        base::TimeTicks() + base::TimeDelta::FromMicroseconds(
+            timestamp * base::Time::kMicrosecondsPerSecond);
+    delay = time_to_send - base::TimeTicks::Now();
+  }
+
+  if (delay.InMilliseconds() <= 0) {
+    SendMIDIDataInternal(handle, data);
+  } else {
+    base::MessageLoop::current()->PostDelayedTask(
+        FROM_HERE,
+        base::Bind(&SendMIDIDataInternal, handle, data),

[scherkus (not reviewing), 2013/11/27 22:07:30]

since handle and data get copied, is it possible for handle to refer to invalid
midi device by time this task runs?

what will happen if SendMIDIDataInternal() runs w/ an invalid handle?

[yukawa, 2013/12/04 17:51:22]

Yeah, your concern was real, although Windows strictly verifies MIDI handles and
most of cases are supposed to cause nothing harmful.

I fixed that problem in the patch set 4.  In short, all we need to do is that to
make sure |send_thread_| is stopped before |out_devices_| is cleared.

Detailed background:
It turned out that MIDI handles will never be invalidated until
midiInClose()/midiOutClose() are called, even when a user has physically
unplugged the MIDI cable.  We actually receives MIM_CLOSE/MOM_CLOSE messages
when the cable is disconnected, but MIDI handles are still valid until we call
midiInClose()/midiOutClose().

+        delay);
+  }
+
+  client->AccumulateMIDIBytesSent(data.size());
+}
+
+MIDIManager* MIDIManager::Create() {
+  return new MIDIManagerWin();
+}
+
+}  // namespace media