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..89dd8c80aac8ac7f896596a1721fa87fdc508b1e 100644
--- a/media/midi/midi_manager.cc
+++ b/media/midi/midi_manager.cc
@@ -43,14 +43,16 @@ void ReportUsage(Usage usage) {
 }  // namespace
 
 MidiManager::MidiManager()
-    : initialized_(false), result_(Result::NOT_INITIALIZED) {
+    : initialized_(false),
+      shutted_down_(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 Shutdown() is called to clean up resources allocated on
+  // the Chrome_IOThread.
+  DCHECK(shutted_down_);

[yhirano, 2015/09/07 06:00:25]

Shouldn't we check that it is correctly finalized?
I'm not sure who ensures the condition, though.

[Takashi Toyoshima, 2015/09/07 19:04:39]

We can do nothing here to recover even if Shutdown() fails. So, I think making
Shutdown returning boolean result and checking it here does not make sense.
It would be easy and reasonable to add DCHECK directly for each operation in
Shutdown().

On the other hand, this shutdown check is useful to write unit tests correctly.

[yhirano, 2015/09/08 04:59:37]

What I'm worrying about is the case where the posted Finalize runs (on the IO
thread) after the MidiManager is destructed (on the main loop thread). Are you
sure there is no such case?

 }
 
 #if !defined(OS_MACOSX) && !defined(OS_WIN) && \
@@ -61,6 +63,17 @@ MidiManager* MidiManager::Create() {
 }
 #endif
 
+void MidiManager::Shutdown() {
+  shutted_down_ = true;
+  UMA_HISTOGRAM_ENUMERATION("Media.Midi.ResultOnShutdown",
+                            static_cast<int>(result_),
+                            static_cast<int>(Result::MAX) + 1);
+  if (session_thread_runner_) {
+    session_thread_runner_->PostTask(
+        FROM_HERE, base::Bind(&MidiManager::Finalize, base::Unretained(this)));
+  }
+}
+
 void MidiManager::StartSession(MidiManagerClient* client) {
   ReportUsage(Usage::SESSION_STARTED);