Manage MIDI related objects and sessions' lifecycles correctly

content/browser/media/midi_host.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 CONTENT_BROWSER_MEDIA_MIDI_HOST_H_
 #define CONTENT_BROWSER_MEDIA_MIDI_HOST_H_
 
 #include <vector>
 
 #include "base/gtest_prod_util.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/scoped_vector.h"
+#include "base/synchronization/lock.h"
 #include "content/common/content_export.h"
 #include "content/public/browser/browser_message_filter.h"
 #include "content/public/browser/browser_thread.h"
 #include "media/midi/midi_manager.h"
 
 namespace media {
 class MidiManager;
 class MidiMessageQueue;
 }
 
 namespace content {
 
 class CONTENT_EXPORT MidiHost
     : public BrowserMessageFilter,
       public media::MidiManagerClient {
  public:
   // Called from UI thread from the owner of this object.
   MidiHost(int renderer_process_id, media::MidiManager* midi_manager);
 
   // BrowserMessageFilter implementation.
   void OnDestruct() const override;
   bool OnMessageReceived(const IPC::Message& message) override;
 
   // MidiManagerClient implementation.
-  void CompleteStartSession(int client_id, media::MidiResult result) override;
+  void CompleteStartSession(media::MidiResult result) override;
   void ReceiveMidiData(uint32 port,
                        const uint8* data,
                        size_t length,
                        double timestamp) override;
   void AccumulateMidiBytesSent(size_t n) override;
 
   // Start session to access MIDI hardware.
-  void OnStartSession(int client_id);
+  void OnStartSession();
 
   // Data to be sent to a MIDI output port.
   void OnSendData(uint32 port,
                   const std::vector<uint8>& data,
                   double timestamp);
 
+  void OnEndSession();
+
  private:
   FRIEND_TEST_ALL_PREFIXES(MidiHostTest, IsValidWebMIDIData);
   friend class base::DeleteHelper<MidiHost>;
   friend class BrowserThread;
 
   ~MidiHost() override;
 
   // Returns true if |data| fulfills the requirements of MidiOutput.send API
   // defined in the WebMIDI spec.
   // - |data| must be any number of complete MIDI messages (data abbreviation
   //    called "running status" is disallowed).
   // - 1-byte MIDI realtime messages can be placed at any position of |data|.
   static bool IsValidWebMIDIData(const std::vector<uint8>& data);
 
   int renderer_process_id_;
 
   // Represents if the renderer has a permission to send/receive MIDI SysEX
   // messages.
   bool has_sys_ex_permission_;
 
+  // Represents if a session is requested to start.
+  bool is_session_requested_;
+
   // |midi_manager_| talks to the platform-specific MIDI APIs.
   // It can be NULL if the platform (or our current implementation)
   // does not support MIDI.  If not supported then a call to
   // OnRequestAccess() will always refuse access and a call to
   // OnSendData() will do nothing.
   media::MidiManager* const midi_manager_;
 
   // Buffers where data sent from each MIDI input port is stored.
   ScopedVector<media::MidiMessageQueue> received_messages_queues_;
 
   // The number of bytes sent to the platform-specific MIDI sending
   // system, but not yet completed.
   size_t sent_bytes_in_flight_;
 
   // The number of bytes successfully sent since the last time
   // we've acknowledged back to the renderer.
   size_t bytes_sent_since_last_acknowledgement_;
 
   // Protects access to |sent_bytes_in_flight_|.
   base::Lock in_flight_lock_;
 
   DISALLOW_COPY_AND_ASSIGN(MidiHost);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_MEDIA_MIDI_HOST_H_