Web MIDI: introduce MidiManager::Shutdown to shutdown gracefully

content/browser/media/midi_host.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 "content/browser/media/midi_host.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/process/process.h"
 #include "base/trace_event/trace_event.h"
@@ skipping 38 matching lines @@
 MidiHost::MidiHost(int renderer_process_id,
                    media::midi::MidiManager* midi_manager)
     : BrowserMessageFilter(MidiMsgStart),
       renderer_process_id_(renderer_process_id),
       has_sys_ex_permission_(false),
       is_session_requested_(false),
       midi_manager_(midi_manager),
       sent_bytes_in_flight_(0),
       bytes_sent_since_last_acknowledgement_(0),
       output_port_count_(0) {
-  CHECK(midi_manager_);
+  DCHECK(midi_manager_);
 }
 
 MidiHost::~MidiHost() {
   // Close an open session, or abort opening a session.
-  if (is_session_requested_)
+  if (is_session_requested_ && midi_manager_)
     midi_manager_->EndSession(this);
 }
 
 void MidiHost::OnDestruct() const {
   BrowserThread::DeleteOnIOThread::Destruct(this);
 }
 
 // IPC Messages handler
 bool MidiHost::OnMessageReceived(const IPC::Message& message) {
   bool handled = true;
   IPC_BEGIN_MESSAGE_MAP(MidiHost, message)
     IPC_MESSAGE_HANDLER(MidiHostMsg_StartSession, OnStartSession)
     IPC_MESSAGE_HANDLER(MidiHostMsg_SendData, OnSendData)
     IPC_MESSAGE_HANDLER(MidiHostMsg_EndSession, OnEndSession)
     IPC_MESSAGE_UNHANDLED(handled = false)
   IPC_END_MESSAGE_MAP()
 
   return handled;
 }
 
 void MidiHost::OnStartSession() {
   is_session_requested_ = true;
-  midi_manager_->StartSession(this);
+  if (midi_manager_)
+    midi_manager_->StartSession(this);
 }
 
 void MidiHost::OnSendData(uint32 port,
                           const std::vector<uint8>& data,
                           double timestamp) {
   {
     base::AutoLock auto_lock(output_port_count_lock_);
     if (output_port_count_ <= port) {
       bad_message::ReceivedBadMessage(this, bad_message::MH_INVALID_MIDI_PORT);
       return;
@@ skipping 17 matching lines @@
 
   {
     base::AutoLock auto_lock(in_flight_lock_);
     // Sanity check that we won't send too much data.
     // TODO(yukawa): Consider to send an error event back to the renderer
     // after some future discussion in W3C.
     if (data.size() + sent_bytes_in_flight_ > kMaxInFlightBytes)
       return;
     sent_bytes_in_flight_ += data.size();
   }
-  midi_manager_->DispatchSendMidiData(this, port, data, timestamp);
+  if (midi_manager_)
+    midi_manager_->DispatchSendMidiData(this, port, data, timestamp);
 }
 
 void MidiHost::OnEndSession() {
   is_session_requested_ = false;
-  midi_manager_->EndSession(this);
+  if (midi_manager_)
+    midi_manager_->EndSession(this);
 }
 
 void MidiHost::CompleteStartSession(media::midi::Result result) {
   DCHECK(is_session_requested_);
   if (result == media::midi::Result::OK) {
     // ChildSecurityPolicy is set just before OnStartSession by
     // MidiDispatcherHost. So we can safely cache the policy.
     has_sys_ex_permission_ = ChildProcessSecurityPolicyImpl::GetInstance()->
         CanSendMidiSysExMessage(renderer_process_id_);
   }
@@ skipping 68 matching lines @@
     bytes_sent_since_last_acknowledgement_ += n;
 
   if (bytes_sent_since_last_acknowledgement_ >=
       kAcknowledgementThresholdBytes) {
     Send(new MidiMsg_AcknowledgeSentData(
         bytes_sent_since_last_acknowledgement_));
     bytes_sent_since_last_acknowledgement_ = 0;
   }
 }
 
+void MidiHost::Detached() {
+  midi_manager_ = nullptr;
+}
+
 // static
 bool MidiHost::IsValidWebMIDIData(const std::vector<uint8>& data) {
   bool in_sysex = false;
   size_t waiting_data_length = 0;
   for (size_t i = 0; i < data.size(); ++i) {
     const uint8 current = data[i];
     if (IsSystemRealTimeMessage(current))
       continue;  // Real time message can be placed at any point.
     if (waiting_data_length > 0) {
       if (!IsDataByte(current))
@@ skipping 14 matching lines @@
     }
     waiting_data_length = media::midi::GetMidiMessageLength(current);
     if (waiting_data_length == 0)
       return false;  // Error: |current| should have been a valid status byte.
     --waiting_data_length;  // Found status byte
   }
   return waiting_data_length == 0 && !in_sysex;
 }
 
 }  // namespace content