Use seq instead of rawmidi for MidiManagerAlsa

media/midi/midi_manager_alsa.cc

 // Copyright 2014 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_alsa.h"
 
 #include <alsa/asoundlib.h>
 #include <stdlib.h>
 #include <algorithm>
 #include <string>
 
 #include "base/bind.h"
 #include "base/logging.h"
 #include "base/memory/ref_counted.h"
 #include "base/message_loop/message_loop.h"
 #include "base/posix/eintr_wrapper.h"
 #include "base/strings/stringprintf.h"
 #include "base/threading/thread.h"
 #include "base/time/time.h"
 #include "media/midi/midi_port_info.h"
 
 namespace media {
 
 namespace {
 
-const size_t kReceiveBufferSize = 4096;
-const unsigned short kPollEventMask = POLLIN | POLLERR | POLLNVAL;
+// Per-output buffer. This can be smaller, but then large sysex messages
+// will be (harmlessly) split across multiple seq events. This should
+// not have any real practical effect, except perhaps to slightly reorder
+// realtime messages with respect to sysex.
+const size_t kSendBufferSize = 256;
+
+// Constants for the capabilities we search for in inputs and outputs.
+// See http://www.alsa-project.org/alsa-doc/alsa-lib/seq.html.
+const unsigned int kRequiredInputPortCaps =
+    SND_SEQ_PORT_CAP_READ | SND_SEQ_PORT_CAP_SUBS_READ;
+const unsigned int kRequiredOutputPortCaps =
+    SND_SEQ_PORT_CAP_WRITE | SND_SEQ_PORT_CAP_SUBS_WRITE;
+
+int AddrToInt(const snd_seq_addr_t* addr) {
+  return (addr->client << 8) | addr->port;
+}
+
+class CardInfo {
+ public:
+  CardInfo(std::string name, std::string manufacturer,

[Takashi Toyoshima, 2014/06/04 20:28:17]

can't we make these arguments const?

[Adam Goode, 2014/06/08 02:52:58]

Yes, by changing to ScopedVector below.

+           std::string driver)
+      : name_(name), manufacturer_(manufacturer), driver_(driver) {
+  }
+  std::string name_;
+  std::string manufacturer_;
+  std::string driver_;
+};
 
 }  // namespace
 
-class MidiManagerAlsa::MidiDeviceInfo
-    : public base::RefCounted<MidiDeviceInfo> {
- public:
-  MidiDeviceInfo(MidiManagerAlsa* manager,
-                 const std::string& bus_id,
-                 snd_ctl_card_info_t* card,
-                 const snd_rawmidi_info_t* midi,
-                 int device) {
-    opened_ = !snd_rawmidi_open(&midi_in_, &midi_out_, bus_id.c_str(), 0);
-    if (!opened_)
-      return;
-
-    const std::string id = base::StringPrintf("%s:%d", bus_id.c_str(), device);
-    const std::string name = snd_rawmidi_info_get_name(midi);
-    // We assume that card longname is in the format of
-    // "<manufacturer> <name> at <bus>". Otherwise, we give up to detect
-    // a manufacturer name here.
-    std::string manufacturer;
-    const std::string card_name = snd_ctl_card_info_get_longname(card);
-    size_t name_index = card_name.find(name);
-    if (std::string::npos != name_index)
-      manufacturer = card_name.substr(0, name_index - 1);
-    const std::string version =
-        base::StringPrintf("%s / ALSA library version %d.%d.%d",
-                           snd_ctl_card_info_get_driver(card),
-                           SND_LIB_MAJOR, SND_LIB_MINOR, SND_LIB_SUBMINOR);
-    port_info_ = MidiPortInfo(id, manufacturer, name, version);
-  }
-
-  void Send(MidiManagerClient* client, const std::vector<uint8>& data) {
-    ssize_t result = snd_rawmidi_write(
-        midi_out_, reinterpret_cast<const void*>(&data[0]), data.size());
-    if (static_cast<size_t>(result) != data.size()) {
-      // TODO(toyoshim): Handle device disconnection.
-      VLOG(1) << "snd_rawmidi_write fails: " << strerror(-result);
-    }
-    base::MessageLoop::current()->PostTask(
-        FROM_HERE,
-        base::Bind(&MidiManagerClient::AccumulateMidiBytesSent,
-                   base::Unretained(client), data.size()));
-  }
-
-  // Read input data from a MIDI input device which is ready to read through
-  // the ALSA library. Called from EventLoop() and read data will be sent to
-  // blink through MIDIManager base class.
-  size_t Receive(uint8* data, size_t length) {
-    return snd_rawmidi_read(midi_in_, reinterpret_cast<void*>(data), length);
-  }
-
-  const MidiPortInfo& GetMidiPortInfo() const { return port_info_; }
-
-  // Get the number of descriptors which is required to call poll() on the
-  // device. The ALSA library always returns 1 here now, but it may be changed
-  // in the future.
-  int GetPollDescriptorsCount() {
-    return snd_rawmidi_poll_descriptors_count(midi_in_);
-  }
-
-  // Following API initializes pollfds for polling the device, and returns the
-  // number of descriptors they are initialized. It must be the same value with
-  // snd_rawmidi_poll_descriptors_count().
-  int SetupPollDescriptors(struct pollfd* pfds, unsigned int count) {
-    return snd_rawmidi_poll_descriptors(midi_in_, pfds, count);
-  }
-
-  unsigned short GetPollDescriptorsRevents(struct pollfd* pfds) {
-    unsigned short revents;
-    snd_rawmidi_poll_descriptors_revents(midi_in_,
-                                         pfds,
-                                         GetPollDescriptorsCount(),
-                                         &revents);
-    return revents;
-  }
-
-  bool IsOpened() const { return opened_; }
-
- private:
-  friend class base::RefCounted<MidiDeviceInfo>;
-  virtual ~MidiDeviceInfo() {
-    if (opened_) {
-      snd_rawmidi_close(midi_in_);
-      snd_rawmidi_close(midi_out_);
-    }
-  }
-
-  bool opened_;
-  MidiPortInfo port_info_;
-  snd_rawmidi_t* midi_in_;
-  snd_rawmidi_t* midi_out_;
-
-  DISALLOW_COPY_AND_ASSIGN(MidiDeviceInfo);
-};
-
 MidiManagerAlsa::MidiManagerAlsa()
-    : send_thread_("MidiSendThread"),
-      event_thread_("MidiEventThread") {
-  for (size_t i = 0; i < arraysize(pipe_fd_); ++i)
-    pipe_fd_[i] = -1;
+    : in_client_(NULL),
+      out_client_(NULL),
+      out_client_id_(-1),
+      in_port_(-1),
+      decoder_(NULL),
+      send_thread_("MidiSendThread"),
+      event_thread_("MidiEventThread"),
+      event_thread_shutdown_(false) {
+  // Initialize decoder.
+  snd_midi_event_new(0, &decoder_);
+  snd_midi_event_no_status(decoder_, 1);
 }
 
 void MidiManagerAlsa::StartInitialization() {
-  // Enumerate only hardware MIDI devices because software MIDIs running in
-  // the browser process is not secure.
+  // TODO(agoode): Move off I/O thread. See http://crbug.com/374341.
+
+  // Create client handles.
+  int err = snd_seq_open(&in_client_, "hw", SND_SEQ_OPEN_INPUT, 0);
+  if (err != 0) {
+    VLOG(1) << "snd_seq_open fails: " << snd_strerror(err);
+    return CompleteInitialization(MIDI_INITIALIZATION_ERROR);
+  }
+  int in_client_id = snd_seq_client_id(in_client_);
+  err = snd_seq_open(&out_client_, "hw", SND_SEQ_OPEN_OUTPUT, 0);
+  if (err != 0) {
+    VLOG(1) << "snd_seq_open fails: " << snd_strerror(err);
+    return CompleteInitialization(MIDI_INITIALIZATION_ERROR);
+  }
+  out_client_id_ = snd_seq_client_id(out_client_);
+
+  // Name the clients.
+  err = snd_seq_set_client_name(in_client_, "Chrome (input)");
+  if (err != 0) {
+    VLOG(1) << "snd_seq_set_client_name fails: " << snd_strerror(err);
+    return CompleteInitialization(MIDI_INITIALIZATION_ERROR);
+  }
+  err = snd_seq_set_client_name(out_client_, "Chrome (output)");
+  if (err != 0) {
+    VLOG(1) << "snd_seq_set_client_name fails: " << snd_strerror(err);
+    return CompleteInitialization(MIDI_INITIALIZATION_ERROR);
+  }
+
+  // Create input port.
+  in_port_ = snd_seq_create_simple_port(in_client_, NULL,
+                                        SND_SEQ_PORT_CAP_WRITE |
+                                        SND_SEQ_PORT_CAP_NO_EXPORT,
+                                        SND_SEQ_PORT_TYPE_MIDI_GENERIC |
+                                        SND_SEQ_PORT_TYPE_APPLICATION);
+  if (in_port_ < 0) {
+    VLOG(1) << "snd_seq_create_simple_port fails: " << snd_strerror(in_port_);
+    return CompleteInitialization(MIDI_INITIALIZATION_ERROR);
+  }
+
+  // Subscribe to the announce port.
+  snd_seq_port_subscribe_t* subs;
+  snd_seq_port_subscribe_alloca(&subs);
+  snd_seq_addr_t announce_sender;
+  snd_seq_addr_t announce_dest;
+  announce_sender.client = SND_SEQ_CLIENT_SYSTEM;
+  announce_sender.port = SND_SEQ_PORT_SYSTEM_ANNOUNCE;
+  announce_dest.client = in_client_id;
+  announce_dest.port = in_port_;
+  snd_seq_port_subscribe_set_sender(subs, &announce_sender);
+  snd_seq_port_subscribe_set_dest(subs, &announce_dest);
+  err = snd_seq_subscribe_port(in_client_, subs);
+  if (err != 0) {
+    VLOG(1) << "snd_seq_subscribe_port on the announce port fails: "
+            << snd_strerror(err);
+    return CompleteInitialization(MIDI_INITIALIZATION_ERROR);
+  }
+
+  // Use a heuristic to extract the list of manufacturers for the hardware MIDI
+  // devices. This won't work for all devices. It is also brittle until
+  // hotplug is implemented. (See http://crbug.com/279097.)
+  // TODO(agoode): Make manufacturer extraction simple and reliable.
+  // http://crbug.com/377250.
+  std::vector<CardInfo> cards;
   snd_ctl_card_info_t* card;
   snd_rawmidi_info_t* midi_out;
   snd_rawmidi_info_t* midi_in;
   snd_ctl_card_info_alloca(&card);
   snd_rawmidi_info_alloca(&midi_out);
   snd_rawmidi_info_alloca(&midi_in);
   for (int index = -1; !snd_card_next(&index) && index >= 0; ) {
     const std::string id = base::StringPrintf("hw:CARD=%i", index);
     snd_ctl_t* handle;
     int err = snd_ctl_open(&handle, id.c_str(), 0);
     if (err != 0) {
       VLOG(1) << "snd_ctl_open fails: " << snd_strerror(err);
       continue;
     }
     err = snd_ctl_card_info(handle, card);
     if (err != 0) {
       VLOG(1) << "snd_ctl_card_info fails: " << snd_strerror(err);
       snd_ctl_close(handle);
       continue;
     }
+    // Enumerate any rawmidi devices (not subdevices) and extract CardInfo.
     for (int device = -1;
-        !snd_ctl_rawmidi_next_device(handle, &device) && device >= 0; ) {
+         !snd_ctl_rawmidi_next_device(handle, &device) && device >= 0; ) {
       bool output;
       bool input;
       snd_rawmidi_info_set_device(midi_out, device);
       snd_rawmidi_info_set_subdevice(midi_out, 0);
       snd_rawmidi_info_set_stream(midi_out, SND_RAWMIDI_STREAM_OUTPUT);
       output = snd_ctl_rawmidi_info(handle, midi_out) == 0;
       snd_rawmidi_info_set_device(midi_in, device);
       snd_rawmidi_info_set_subdevice(midi_in, 0);
       snd_rawmidi_info_set_stream(midi_in, SND_RAWMIDI_STREAM_INPUT);
       input = snd_ctl_rawmidi_info(handle, midi_in) == 0;
       if (!output && !input)
         continue;
-      scoped_refptr<MidiDeviceInfo> port = new MidiDeviceInfo(
-          this, id, card, output ? midi_out : midi_in, device);
-      if (!port->IsOpened()) {
-        VLOG(1) << "MidiDeviceInfo open fails";
-        continue;
+
+      snd_rawmidi_info_t* midi = midi_out ? midi_out : midi_in;
+      const std::string name = snd_rawmidi_info_get_name(midi);
+      // We assume that card longname is in the format of
+      // "<manufacturer> <name> at <bus>". Otherwise, we give up to detect
+      // a manufacturer name here.
+      std::string manufacturer;
+      const std::string card_name = snd_ctl_card_info_get_longname(card);
+      size_t at_index = card_name.rfind(" at ");
+      if (std::string::npos != at_index) {
+        size_t name_index = card_name.rfind(name, at_index - 1);
+        if (std::string::npos != name_index)
+          manufacturer = card_name.substr(0, name_index - 1);
       }
-      if (input) {
-        in_devices_.push_back(port);
-        AddInputPort(port->GetMidiPortInfo());
+      const std::string driver = snd_ctl_card_info_get_driver(card);
+      cards.push_back(CardInfo(name, manufacturer, driver));
+    }
+  }
+
+  // Enumerate all ports in all clients.
+  snd_seq_client_info_t* client_info;
+  snd_seq_client_info_alloca(&client_info);
+  snd_seq_port_info_t* port_info;
+  snd_seq_port_info_alloca(&port_info);
+
+  snd_seq_client_info_set_client(client_info, -1);
+  // Enumerate clients.
+  uint32 current_input = 0;
+  unsigned int current_card = 0;
+  while (!snd_seq_query_next_client(in_client_, client_info)) {
+    int client_id = snd_seq_client_info_get_client(client_info);
+    if ((client_id == in_client_id) || (client_id == out_client_id_)) {
+      // Skip our own clients.
+      continue;
+    }
+    const std::string client_name = snd_seq_client_info_get_name(client_info);
+    snd_seq_port_info_set_client(port_info, client_id);
+    snd_seq_port_info_set_port(port_info, -1);
+
+    std::string manufacturer;
+    std::string driver;
+    // In the current Alsa kernel implementation, hardware clients match the
+    // cards in the same order.
+    if ((snd_seq_client_info_get_type(client_info) == SND_SEQ_KERNEL_CLIENT) &&
+        (current_card < cards.size())) {
+      CardInfo info = cards[current_card];

[Takashi Toyoshima, 2014/06/04 20:28:17]

const CardInfo

[Adam Goode, 2014/06/08 02:52:58]

Done.

+      if (info.name_ == client_name) {
+        manufacturer = info.manufacturer_;
+        driver = info.driver_;
+        current_card++;
       }
-      if (output) {
-        out_devices_.push_back(port);
-        AddOutputPort(port->GetMidiPortInfo());
+    }
+    // Enumerate ports.
+    while (!snd_seq_query_next_port(in_client_, port_info)) {
+      unsigned int port_type = snd_seq_port_info_get_type(port_info);
+      if (port_type & SND_SEQ_PORT_TYPE_MIDI_GENERIC) {
+        const snd_seq_addr_t* addr = snd_seq_port_info_get_addr(port_info);
+        const std::string name = snd_seq_port_info_get_name(port_info);
+        const std::string id = base::StringPrintf("%d:%d %s",
+                                                  addr->client,
+                                                  addr->port,
+                                                  name.c_str());
+        std::string version;
+        if (driver != "") {
+          version = driver + " / ";
+        }
+        version += base::StringPrintf("ALSA library version %d.%d.%d",
+                                      SND_LIB_MAJOR,
+                                      SND_LIB_MINOR,
+                                      SND_LIB_SUBMINOR);
+        unsigned int caps = snd_seq_port_info_get_capability(port_info);
+        if ((caps & kRequiredInputPortCaps) == kRequiredInputPortCaps) {
+          // Subscribe to this port.
+          const snd_seq_addr_t* sender = snd_seq_port_info_get_addr(port_info);
+          snd_seq_addr_t dest;
+          dest.client = snd_seq_client_id(in_client_);
+          dest.port = in_port_;
+          snd_seq_port_subscribe_set_sender(subs, sender);
+          snd_seq_port_subscribe_set_dest(subs, &dest);
+          err = snd_seq_subscribe_port(in_client_, subs);
+          if (err != 0) {
+            VLOG(1) << "snd_seq_subscribe_port fails: " << snd_strerror(err);
+          } else {
+            source_map_[AddrToInt(sender)] = current_input++;
+            AddInputPort(MidiPortInfo(id, manufacturer, name, version));
+          }
+        }
+        if ((caps & kRequiredOutputPortCaps) == kRequiredOutputPortCaps) {
+          // Create a port for us to send on.
+          int out_port =
+              snd_seq_create_simple_port(out_client_, NULL,
+                                         SND_SEQ_PORT_CAP_READ |
+                                         SND_SEQ_PORT_CAP_NO_EXPORT,
+                                         SND_SEQ_PORT_TYPE_MIDI_GENERIC |
+                                         SND_SEQ_PORT_TYPE_APPLICATION);
+          if (out_port < 0) {
+            VLOG(1) << "snd_seq_create_simple_port fails: "
+                    << snd_strerror(out_port);
+            // Skip this output port for now.
+            continue;
+          }
+
+          // Activate port subscription.
+          snd_seq_addr_t sender;
+          const snd_seq_addr_t* dest = snd_seq_port_info_get_addr(port_info);
+          sender.client = snd_seq_client_id(out_client_);
+          sender.port = out_port;
+          snd_seq_port_subscribe_set_sender(subs, &sender);
+          snd_seq_port_subscribe_set_dest(subs, dest);
+          err = snd_seq_subscribe_port(out_client_, subs);
+          if (err != 0) {
+            VLOG(1) << "snd_seq_subscribe_port fails: " << snd_strerror(err);
+            snd_seq_delete_simple_port(out_client_, out_port);
+          } else {
+            snd_midi_event_t* encoder;
+            snd_midi_event_new(kSendBufferSize, &encoder);
+            encoders_.push_back(encoder);
+            out_ports_.push_back(out_port);
+            AddOutputPort(MidiPortInfo(id, manufacturer, name, version));
+          }
+        }
       }
     }
-    snd_ctl_close(handle);
-  }
-
-  if (pipe(pipe_fd_) < 0) {
-    VPLOG(1) << "pipe() failed";
-    CompleteInitialization(MIDI_INITIALIZATION_ERROR);
-  } else {
-    event_thread_.Start();
-    event_thread_.message_loop()->PostTask(
-        FROM_HERE,
-        base::Bind(&MidiManagerAlsa::EventReset, base::Unretained(this)));
-    CompleteInitialization(MIDI_OK);
-  }
+  }
+
+  event_thread_.Start();
+  event_thread_.message_loop()->PostTask(
+      FROM_HERE,
+      base::Bind(&MidiManagerAlsa::EventReset, base::Unretained(this)));
+
+  CompleteInitialization(MIDI_OK);
 }
 
 MidiManagerAlsa::~MidiManagerAlsa() {
-  // Send a shutdown message to awake |event_thread_| from poll().
-  if (pipe_fd_[1] >= 0)
-    HANDLE_EINTR(write(pipe_fd_[1], "Q", 1));
-
-  // Stop receiving messages.
+  // Tell the event thread it will soon be time to shut down. This gives
+  // us assurance the thread will stop in case the SND_SEQ_EVENT_CLIENT_EXIT
+  // message is lost.
+  {
+    base::AutoLock lock(shutdown_lock_);
+    event_thread_shutdown_ = true;
+  }
+
+  // Stop the send thread.
+  send_thread_.Stop();
+
+  // Close the out client. This will trigger the event thread to stop,
+  // because of SND_SEQ_EVENT_CLIENT_EXIT.
+  if (out_client_)
+    snd_seq_close(out_client_);
+
+  // Wait for the event thread to stop.
   event_thread_.Stop();
 
-  for (int i = 0; i < 2; ++i) {
-    if (pipe_fd_[i] >= 0)
-      close(pipe_fd_[i]);
-  }
-  send_thread_.Stop();
+  // Close the in client.
+  if (in_client_)
+    snd_seq_close(in_client_);
+
+  // Free the decoder.
+  snd_midi_event_free(decoder_);
+
+  // Free the encoders.
+  for (EncoderList::iterator i = encoders_.begin(); i != encoders_.end(); ++i)
+    snd_midi_event_free(*i);
+}
+
+void MidiManagerAlsa::SendMidiData(uint32 port_index,
+                                   const std::vector<uint8>& data) {
+  DCHECK(send_thread_.message_loop_proxy()->BelongsToCurrentThread());
+
+  snd_midi_event_t* encoder = encoders_[port_index];
+  for (unsigned int i = 0; i < data.size(); i++) {
+    snd_seq_event_t event;
+    int result = snd_midi_event_encode_byte(encoder, data[i], &event);
+    if (result == 1) {
+      // Full event, send it.
+      snd_seq_ev_set_source(&event, out_ports_[port_index]);
+      snd_seq_ev_set_subs(&event);
+      snd_seq_ev_set_direct(&event);
+      snd_seq_event_output_direct(out_client_, &event);
+    }
+  }
 }
 
 void MidiManagerAlsa::DispatchSendMidiData(MidiManagerClient* client,
                                            uint32 port_index,
                                            const std::vector<uint8>& data,
                                            double timestamp) {
-  if (out_devices_.size() <= port_index)
+  if (out_ports_.size() <= port_index)
     return;
 
+  // Not correct right now. http://crbug.com/374341.
+  if (!send_thread_.IsRunning())
+    send_thread_.Start();
+
   base::TimeDelta delay;
   if (timestamp != 0.0) {
     base::TimeTicks time_to_send =
         base::TimeTicks() + base::TimeDelta::FromMicroseconds(
             timestamp * base::Time::kMicrosecondsPerSecond);
     delay = std::max(time_to_send - base::TimeTicks::Now(), base::TimeDelta());
   }
 
-  if (!send_thread_.IsRunning())
-    send_thread_.Start();
-
-  scoped_refptr<MidiDeviceInfo> device = out_devices_[port_index];
   send_thread_.message_loop()->PostDelayedTask(
       FROM_HERE,
-      base::Bind(&MidiDeviceInfo::Send, device, client, data),
-      delay);
+      base::Bind(&MidiManagerAlsa::SendMidiData, base::Unretained(this),
+                 port_index, data), delay);
+
+  // Acknowledge send.
+  send_thread_.message_loop()->PostTask(
+      FROM_HERE,
+      base::Bind(&MidiManagerClient::AccumulateMidiBytesSent,
+                 base::Unretained(client), data.size()));
 }
 
 void MidiManagerAlsa::EventReset() {
-  CHECK_GE(pipe_fd_[0], 0);
-
-  // Sum up descriptors which are needed to poll input devices and a shutdown
-  // message.
-  // Keep the first one descriptor for a shutdown message.
-  size_t poll_fds_size = 1;
-  for (size_t i = 0; i < in_devices_.size(); ++i)
-    poll_fds_size += in_devices_[i]->GetPollDescriptorsCount();
-  poll_fds_.resize(poll_fds_size);
-
-  // Setup struct pollfd to poll input MIDI devices and a shutdown message.
-  // The first pollfd is for a shutdown message.
-  poll_fds_[0].fd = pipe_fd_[0];
-  poll_fds_[0].events = kPollEventMask;
-  int fds_index = 1;
-  for (size_t i = 0; i < in_devices_.size(); ++i) {
-    fds_index += in_devices_[i]->SetupPollDescriptors(
-        &poll_fds_[fds_index], poll_fds_.size() - fds_index);
-  }
-
   event_thread_.message_loop()->PostTask(
       FROM_HERE,
       base::Bind(&MidiManagerAlsa::EventLoop, base::Unretained(this)));
 }
 
 void MidiManagerAlsa::EventLoop() {
-  if (HANDLE_EINTR(poll(&poll_fds_[0], poll_fds_.size(), -1)) < 0) {
-    VPLOG(1) << "Couldn't poll(). Stop to poll input MIDI devices.";
-    // TODO(toyoshim): Handle device disconnection, and try to reconnect?
-    return;
-  }
+  // Read available incoming MIDI data.
+  snd_seq_event_t* event;
+  int err = snd_seq_event_input(in_client_, &event);
+  double timestamp =
+      (base::TimeTicks::HighResNow() - base::TimeTicks()).InSecondsF();
+  if (err == -ENOSPC) {
+    VLOG(1) << "snd_seq_event_input detected buffer overrun";
 
-  // Check timestamp as soon as possible because the API requires accurate
-  // timestamp as possible. It will be useful for recording MIDI events.
-  base::TimeTicks now = base::TimeTicks::HighResNow();
+      // We've lost events: check another way to see if we need to shut down.
+      base::AutoLock lock(shutdown_lock_);
+      if (event_thread_shutdown_) {
+        return;
+      }
+  } else if (err < 0) {
+      VLOG(1) << "snd_seq_event_input fails: " << snd_strerror(err);
+      return;
+  } else {
+    // Check for disconnection of out client. This means "shut down".
+    if (event->source.client == SND_SEQ_CLIENT_SYSTEM &&
+        event->source.port == SND_SEQ_PORT_SYSTEM_ANNOUNCE &&
+        event->type == SND_SEQ_EVENT_CLIENT_EXIT &&
+        event->data.addr.client == out_client_id_) {
+      return;
+    }
 
-  // Is this thread going to be shutdown?
-  if (poll_fds_[0].revents & kPollEventMask)
-    return;
-
-  // Read available incoming MIDI data.
-  int fds_index = 1;
-  uint8 buffer[kReceiveBufferSize];
-
-  for (size_t i = 0; i < in_devices_.size(); ++i) {
-    unsigned short revents =
-        in_devices_[i]->GetPollDescriptorsRevents(&poll_fds_[fds_index]);
-    if (revents & (POLLERR | POLLNVAL)) {
-      // TODO(toyoshim): Handle device disconnection.
-      VLOG(1) << "snd_rawmidi_descriptors_revents fails";
-      poll_fds_[fds_index].events = 0;
+    std::map<int, uint32>::iterator source_it =
+        source_map_.find(AddrToInt(&event->source));
+    if (source_it != source_map_.end()) {
+      uint32 source = source_it->second;
+      if (event->type == SND_SEQ_EVENT_SYSEX) {
+        // Special! Variable-length sysex.
+        ReceiveMidiData(source, static_cast<const uint8*>(event->data.ext.ptr),
+                        event->data.ext.len,
+                        timestamp);
+      } else {
+        // Otherwise, decode this and send that on.
+        unsigned char buf[12];
+        long count = snd_midi_event_decode(decoder_, buf, sizeof(buf), event);
+        if (count <= 0) {
+          if (count != -ENOENT) {
+            // ENOENT means that it's not a MIDI message, which is not an
+            // error, but other negative values are errors for us.
+            VLOG(1) << "snd_midi_event_decoder fails " << snd_strerror(count);
+          }
+        } else {
+          ReceiveMidiData(source, buf, count, timestamp);
+        }
+      }
     }
-    if (revents & POLLIN) {
-      size_t read_size = in_devices_[i]->Receive(buffer, kReceiveBufferSize);
-      ReceiveMidiData(i, buffer, read_size, now);
-    }
-    fds_index += in_devices_[i]->GetPollDescriptorsCount();
   }
 
   // Do again.
   event_thread_.message_loop()->PostTask(
       FROM_HERE,
       base::Bind(&MidiManagerAlsa::EventLoop, base::Unretained(this)));
 }
 
 MidiManager* MidiManager::Create() {
   return new MidiManagerAlsa();
 }
 
 }  // namespace media