Web MIDI: introduce MidiManager::Shutdown to shutdown gracefully

media/midi/midi_manager.h

 // 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.
 
 #ifndef MEDIA_MIDI_MIDI_MANAGER_H_
 #define MEDIA_MIDI_MIDI_MANAGER_H_
 
 #include <set>
 #include <vector>
 
@@ skipping 42 matching lines @@
   // |timestamp| is the time the data was received, in seconds.
   virtual void ReceiveMidiData(uint32 port_index,
                                const uint8* data,
                                size_t length,
                                double timestamp) = 0;
 
   // AccumulateMidiBytesSent() is called to acknowledge when bytes have
   // successfully been sent to the hardware.
   // This happens as a result of the client having previously called
   // MidiManager::DispatchSendMidiData().
   virtual void AccumulateMidiBytesSent(size_t n) = 0;

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

Should we have Detach() which will be called in Finalize()?

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

Do you already have any real concerns in client side on shutdown?
Otherwise, let me just leave TODO here.

[yhirano, 2015/09/28 07:50:00]

0: A MidiManager m has a client c.
1: m->Shutdown is called on the main thread.
2: m->Finalize is called on the IO thread.
3: m->DispatchSendData is called on the IO thread by c.

Is this unrealistic?

[Takashi Toyoshima, 2015/10/02 15:19:24]

I see. Let me fix this.

 };
 
 // Manages access to all MIDI hardware.
 class MIDI_EXPORT MidiManager {
  public:
   static const size_t kMaxPendingClientCount = 128;
 
   MidiManager();
   virtual ~MidiManager();
 
   // The constructor and the destructor will be called on the CrBrowserMain
   // thread.
   static MidiManager* Create();
 
+  // Called on the CrBrowserMain thread to notify the Chrome_IOThread will stop
+  // and the instance will be destructed on the CrBrowserMain thread soon.
+  void Shutdown();
+
   // A client calls StartSession() to receive and send MIDI data.
   // If the session is ready to start, the MIDI system is lazily initialized
   // and the client is registered to receive MIDI data.
   // CompleteStartSession() is called with Result::OK if the session is started.
   // Otherwise CompleteStartSession() is called with proper Result code.
   // StartSession() and EndSession() can be called on the Chrome_IOThread.
   // CompleteStartSession() will be invoked on the same Chrome_IOThread.
   void StartSession(MidiManagerClient* client);
 
   // A client calls EndSession() to stop receiving MIDI data.
@@ skipping 24 matching lines @@
   // default implementation that synchronously calls CompleteInitialization()
   // with Result::NOT_SUPPORTED on the caller thread. A derived class for a
   // specific platform should override this method correctly.
   // This method is called on Chrome_IOThread thread inside StartSession().
   // Platform dependent initialization can be processed synchronously or
   // asynchronously. When the initialization is completed,
   // CompleteInitialization() should be called with |result|.
   // |result| should be Result::OK on success, otherwise a proper Result.
   virtual void StartInitialization();
 
+  // Finalizes the platform dependent MIDI system. Called on Chrome_IOThread
+  // thread and the thread will stop immediately after this call.
+  // Platform dependent resources that were allocated on the Chrome_IOThread
+  // should be disposed inside this method.
+  virtual void Finalize() {}
+
   // Called from a platform dependent implementation of StartInitialization().
   // It invokes CompleteInitializationInternal() on the thread that calls
   // StartSession() and distributes |result| to MIDIManagerClient objects in
   // |pending_clients_|.
   void CompleteInitialization(Result result);
 
   void AddInputPort(const MidiPortInfo& info);
   void AddOutputPort(const MidiPortInfo& info);
   void SetInputPortState(uint32 port_index, MidiPortState state);
   void SetOutputPortState(uint32 port_index, MidiPortState state);
@@ skipping 15 matching lines @@
   }
 
   size_t clients_size_for_testing() const { return clients_.size(); }
   size_t pending_clients_size_for_testing() const {
     return pending_clients_.size();
   }
 
  private:
   void CompleteInitializationInternal(Result result);
   void AddInitialPorts(MidiManagerClient* client);
+  void ShutdownOnSessionThread();
 
   // Keeps track of all clients who wish to receive MIDI data.
   typedef std::set<MidiManagerClient*> ClientSet;
   ClientSet clients_;
 
   // Keeps track of all clients who are waiting for CompleteStartSession().
   ClientSet pending_clients_;
 
   // Keeps a SingleThreadTaskRunner of the thread that calls StartSession in
   // order to invoke CompleteStartSession() on the thread.
   scoped_refptr<base::SingleThreadTaskRunner> session_thread_runner_;
 
   // Keeps true if platform dependent initialization is already completed.
   bool initialized_;
 
+  // Keeps false until Finalize() is called.
+  bool finalized_;
+
   // Keeps the platform dependent initialization result if initialization is
   // completed. Otherwise keeps Result::NOT_INITIALIZED.
   Result result_;
 
   // Keeps all MidiPortInfo.
   MidiPortInfoList input_ports_;
   MidiPortInfoList output_ports_;
 
-  // Protects access to |clients_|, |pending_clients_|, |initialized_|,
-  // |result_|, |input_ports_| and |output_ports_|.
+  // Protects access to |clients_|, |pending_clients_|,
+  // |session_thread_runner_|, |initialized_|, |finalize_|, |result_|,
+  // |input_ports_| and |output_ports_|.
   base::Lock lock_;
 
   DISALLOW_COPY_AND_ASSIGN(MidiManager);
 };
 
 }  // namespace midi
 }  // namespace media
 
 #endif  // MEDIA_MIDI_MIDI_MANAGER_H_