Web MIDI: introduce MidiManager::Shutdown to shutdown gracefully

media/midi/midi_manager.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.h"
 
 #include "base/bind.h"
 #include "base/message_loop/message_loop.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/trace_event/trace_event.h"
@@ skipping 25 matching lines @@
 
 void ReportUsage(Usage usage) {
   UMA_HISTOGRAM_ENUMERATION("Media.Midi.Usage",
                             static_cast<Sample>(usage),
                             static_cast<Sample>(Usage::MAX) + 1);
 }
 
 }  // namespace
 
 MidiManager::MidiManager()
-    : initialized_(false), result_(Result::NOT_INITIALIZED) {
+    : initialized_(false), finalized_(false), result_(Result::NOT_INITIALIZED) {
   ReportUsage(Usage::CREATED);
 }
 
 MidiManager::~MidiManager() {
-  UMA_HISTOGRAM_ENUMERATION("Media.Midi.ResultOnShutdown",
-                            static_cast<Sample>(result_),
-                            static_cast<Sample>(Result::MAX) + 1);
+  // Make sure that Finalize() is called to clean up resources allocated on
+  // the Chrome_IOThread.
+  DCHECK(finalized_);
 }
 
 #if !defined(OS_MACOSX) && !defined(OS_WIN) && \
     !(defined(USE_ALSA) && defined(USE_UDEV)) && !defined(OS_ANDROID)
 MidiManager* MidiManager::Create() {
   ReportUsage(Usage::CREATED_ON_UNSUPPORTED_PLATFORMS);
   return new MidiManager;
 }
 #endif
 
+void MidiManager::Shutdown() {
+  UMA_HISTOGRAM_ENUMERATION("Media.Midi.ResultOnShutdown",
+                            static_cast<int>(result_),
+                            static_cast<int>(Result::MAX) + 1);
+  if (session_thread_runner_) {

[yhirano, 2015/09/10 07:37:29]

We need to protect more code with lock in order to avoid
initialized-but-not-finalized situations.

With the current code, StartSession and Shutdown may run in the same time and
MiniManager will get confused then.

In addition to that, it seems possible to run StartSession after Shutdown is
called (or, even after Finalize is done).

[Takashi Toyoshima, 2015/09/10 08:19:15]

You are right. I change code to protect session_thread_runner and remove the
race situations around StartInitialization, CompleteInitialization, and
Finalize.

+    session_thread_runner_->PostTask(
+        FROM_HERE, base::Bind(&MidiManager::ShutdownOnSessionThread,
+                              base::Unretained(this)));
+  } else {
+    base::AutoLock auto_lock(lock_);
+    finalized_ = true;
+  }
+}
+
 void MidiManager::StartSession(MidiManagerClient* client) {
   ReportUsage(Usage::SESSION_STARTED);
 
   bool session_is_ready;
   bool session_needs_initialization = false;
   bool too_many_pending_clients_exist = false;
 
   {
     base::AutoLock auto_lock(lock_);
     session_is_ready = initialized_;
@@ skipping 161 matching lines @@
 
 void MidiManager::AddInitialPorts(MidiManagerClient* client) {
   lock_.AssertAcquired();
 
   for (const auto& info : input_ports_)
     client->AddInputPort(info);
   for (const auto& info : output_ports_)
     client->AddOutputPort(info);
 }
 
+void MidiManager::ShutdownOnSessionThread() {
+  Finalize();
+  base::AutoLock auto_lock(lock_);
+  finalized_ = true;
+}
+
 }  // namespace midi
 }  // namespace media