MidiScheduler binds to task runner of constructing thread

media/midi/midi_manager_usb.h

 // Copyright 2014 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_USB_H_
 #define MEDIA_MIDI_MIDI_MANAGER_USB_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <memory>
 #include <utility>
 #include <vector>
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/compiler_specific.h"
 #include "base/containers/hash_tables.h"
 #include "base/macros.h"
+#include "base/synchronization/lock.h"
 #include "base/time/time.h"
 #include "media/midi/midi_manager.h"
 #include "media/midi/usb_midi_device.h"
 #include "media/midi/usb_midi_export.h"
 #include "media/midi/usb_midi_input_stream.h"
 #include "media/midi/usb_midi_jack.h"
 #include "media/midi/usb_midi_output_stream.h"
 
 namespace media {
 namespace midi {
 
 class MidiScheduler;
 
 // MidiManager for USB-MIDI.
 class USB_MIDI_EXPORT MidiManagerUsb
     : public MidiManager,
       public UsbMidiDeviceDelegate,
       NON_EXPORTED_BASE(public UsbMidiInputStream::Delegate) {
  public:
   explicit MidiManagerUsb(
       std::unique_ptr<UsbMidiDevice::Factory> device_factory);
   ~MidiManagerUsb() override;
 
   // MidiManager implementation.
   void StartInitialization() override;
+  void Finalize() override;
   void DispatchSendMidiData(MidiManagerClient* client,
                             uint32_t port_index,
                             const std::vector<uint8_t>& data,
                             double timestamp) override;
 
   // UsbMidiDeviceDelegate implementation.
   void ReceiveUsbMidiData(UsbMidiDevice* device,
                           int endpoint_number,
                           const uint8_t* data,
                           size_t size,
@@ skipping 28 matching lines @@
   std::unique_ptr<UsbMidiDevice::Factory> device_factory_;
   ScopedVector<UsbMidiDevice> devices_;
   ScopedVector<UsbMidiOutputStream> output_streams_;
   std::unique_ptr<UsbMidiInputStream> input_stream_;
 
   base::Callback<void(Result result)> initialize_callback_;
 
   // A map from <endpoint_number, cable_number> to the index of input jacks.
   base::hash_map<std::pair<int, int>, size_t> input_jack_dictionary_;
 
+  // Lock to ensure the MidiScheduler is being destructed only once in
+  // Finalize() on Chrome_IOThread.
+  base::Lock scheduler_lock_;
   std::unique_ptr<MidiScheduler> scheduler_;
 
   DISALLOW_COPY_AND_ASSIGN(MidiManagerUsb);
 };
 
 }  // namespace midi
 }  // namespace media
 
 #endif  // MEDIA_MIDI_MIDI_MANAGER_USB_H_