MidiScheduler binds to task runner of constructing thread

media/midi/midi_manager_android.h

 // Copyright 2015 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_ANDROID_H_
 #define MEDIA_MIDI_MIDI_MANAGER_ANDROID_H_
 
 #include <jni.h>
 #include <stddef.h>
 #include <stdint.h>
 
 #include <memory>
 #include <vector>
 
 #include "base/android/scoped_java_ref.h"
 #include "base/containers/hash_tables.h"
 #include "base/memory/scoped_vector.h"
+#include "base/synchronization/lock.h"
 #include "base/time/time.h"
 #include "media/midi/midi_input_port_android.h"
 #include "media/midi/midi_manager.h"
 #include "media/midi/midi_scheduler.h"
 
 namespace media {
 namespace midi {
 
 class MidiDeviceAndroid;
 class MidiOutputPortAndroid;
 
 // MidiManagerAndroid is a MidiManager subclass for Android M or newer. For
 // older android OSes, we use MidiManagerUsb.
 class MidiManagerAndroid final : public MidiManager,
                                  public MidiInputPortAndroid::Delegate {
  public:
   MidiManagerAndroid();
   ~MidiManagerAndroid() 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;
 
   // MidiInputPortAndroid::Delegate implementation.
   void OnReceivedData(MidiInputPortAndroid*,
                       const uint8_t* data,
                       size_t size,
                       base::TimeTicks timestamp) override;
@@ skipping 25 matching lines @@
   std::vector<MidiInputPortAndroid*> all_input_ports_;
   // A dictionary from a port to its index.
   // input_port_to_index_[all_input_ports_[i]] == i for each valid |i|.
   base::hash_map<MidiInputPortAndroid*, size_t> input_port_to_index_;
 
   // Ditto for output ports.
   std::vector<MidiOutputPortAndroid*> all_output_ports_;
   base::hash_map<MidiOutputPortAndroid*, size_t> output_port_to_index_;
 
   base::android::ScopedJavaGlobalRef<jobject> raw_manager_;
-  std::unique_ptr<MidiScheduler> scheduler_;
+
+  // Lock to ensure the MidiScheduler is being destructed only once in
+  // Finalize() on Chrome_IOThread.
+  base::Lock scheduler_lock_;
+  std::unique_ptr<MidiScheduler> scheduler_;  // GUARDED_BY(scheduler_lock_)
 };
 
 }  // namespace midi
 }  // namespace media
 
 #endif  // MEDIA_MIDI_MIDI_MANAGER_ANDROID_H_