Web MIDI: introduce MidiManager::Shutdown to shutdown gracefully

media/midi/midi_manager.cc

Index: media/midi/midi_manager.cc
diff --git a/media/midi/midi_manager.cc b/media/midi/midi_manager.cc
index 6e8c1a266fa86502407d929db218eb1e85afc1f5..90e0c91334b87d5f1e42cbcc85d7e2a60cfc65ce 100644
--- a/media/midi/midi_manager.cc
+++ b/media/midi/midi_manager.cc
@@ -43,14 +43,14 @@ void ReportUsage(Usage usage) {
 }  // 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) && \
@@ -61,6 +61,21 @@ MidiManager* MidiManager::Create() {
 }
 #endif
 
+void MidiManager::Shutdown() {
+  UMA_HISTOGRAM_ENUMERATION("Media.Midi.ResultOnShutdown",
+                            static_cast<int>(result_),
+                            static_cast<int>(Result::MAX) + 1);
+  base::AutoLock auto_lock(lock_);
+  if (session_thread_runner_) {
+    session_thread_runner_->PostTask(
+        FROM_HERE, base::Bind(&MidiManager::ShutdownOnSessionThread,
+                              base::Unretained(this)));
+    session_thread_runner_ = nullptr;
+  } else {
+    finalized_ = true;
+  }
+}
+
 void MidiManager::StartSession(MidiManagerClient* client) {
   ReportUsage(Usage::SESSION_STARTED);
 
@@ -95,8 +110,13 @@ void MidiManager::StartSession(MidiManagerClient* client) {
   if (!session_is_ready) {
     if (session_needs_initialization) {
       TRACE_EVENT0("midi", "MidiManager::StartInitialization");
-      session_thread_runner_ =
-          base::MessageLoop::current()->task_runner();
+      {
+        base::AutoLock auto_lock(lock_);
+        // Stop calling StartInitialization() if Shutdown() was already called.
+        if (finalized_)

[yhirano, 2015/09/11 15:59:47]

Should we call CompleteStartSession with INITIALIZATION_ERROR?

[Takashi Toyoshima, 2015/09/17 07:30:49]

This isn't easy because I do not want to call client callback inside a lock. Let
me clean up StartSession().

+          return;
+        session_thread_runner_ = base::MessageLoop::current()->task_runner();
+      }
       StartInitialization();
     }
     if (too_many_pending_clients_exist) {
@@ -154,14 +174,12 @@ void MidiManager::StartInitialization() {
 }
 
 void MidiManager::CompleteInitialization(Result result) {
-  DCHECK(session_thread_runner_.get());
-  // It is safe to post a task to the IO thread from here because the IO thread
-  // should have stopped if the MidiManager is going to be destructed.
-  session_thread_runner_->PostTask(
-      FROM_HERE,
-      base::Bind(&MidiManager::CompleteInitializationInternal,
-                 base::Unretained(this),
-                 result));
+  base::AutoLock auto_lock(lock_);
+  if (session_thread_runner_) {
+    session_thread_runner_->PostTask(
+        FROM_HERE, base::Bind(&MidiManager::CompleteInitializationInternal,
+                              base::Unretained(this), result));
+  }
 }
 
 void MidiManager::AddInputPort(const MidiPortInfo& info) {
@@ -242,5 +260,11 @@ void MidiManager::AddInitialPorts(MidiManagerClient* client) {
     client->AddOutputPort(info);
 }
 
+void MidiManager::ShutdownOnSessionThread() {
+  Finalize();
+  base::AutoLock auto_lock(lock_);
+  finalized_ = true;
+}
+
 }  // namespace midi
 }  // namespace media