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..abd91bea7cc9ebc70e62622f8edc6e86524baee4 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 +61,20 @@ MidiManager* MidiManager::Create() {
 }
 #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);
 
@@ -242,5 +256,11 @@ void MidiManager::AddInitialPorts(MidiManagerClient* client) {
     client->AddOutputPort(info);
 }
 
+void MidiManager::ShutdownOnSessionThread() {
+  Finalize();
+  base::AutoLock auto_lock(lock_);
+  finalized_ = true;
+}
+
 }  // namespace midi
 }  // namespace media