[not for review] Web MIDI: new backend to support dynamic instantiation on Windows

media/midi/dynamically_initialized_midi_manager_win.h

Index: media/midi/dynamically_initialized_midi_manager_win.h
diff --git a/media/midi/dynamically_initialized_midi_manager_win.h b/media/midi/dynamically_initialized_midi_manager_win.h
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+// Copyright 2017 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_DYNAMICALLY_INITIALIZED_MIDI_MANAGER_WIN_H_
+#define MEDIA_MIDI_DYNAMICALLY_INITIALIZED_MIDI_MANAGER_WIN_H_
+
+#include <memory>
+#include <vector>
+
+#include "base/callback_forward.h"
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/system_monitor/system_monitor.h"
+#include "media/midi/midi_manager.h"
+
+namespace base {
+class SingleThreadTaskRunner;
+class TimeDelta;
+}  // namespace base
+
+namespace midi {
+
+// New backend for legacy Windows that support dynamic instantiation.
+class DynamicallyInitializedMidiManagerWin final
+    : public MidiManager,
+      public base::SystemMonitor::DevicesChangedObserver {
+ public:
+  explicit DynamicallyInitializedMidiManagerWin(MidiService* service);
+  ~DynamicallyInitializedMidiManagerWin() override;
+
+  // Calculates event time from elapsed time that system provides.
+  base::TimeTicks CalculateInEventTime(size_t index, uint32_t elapsed_ms) const;
+
+  // Handles MIDI inport event posted from a thread system provides.
+  void ReceiveMidiData(uint32_t index,
+                       const std::vector<uint8_t>& data,
+                       base::TimeTicks time);
+
+  // Posts a reply task to the I/O thread that hosts MidiManager instance, runs
+  // it safely, and ensures that the instance keeps alive while the task is
+  // running.
+  void PostReplyTask(const base::Closure&);
+
+  // MidiManager overrides:
+  void StartInitialization() override;
+  void Finalize() override;
+  void DispatchSendMidiData(MidiManagerClient* client,
+                            uint32_t port_index,
+                            const std::vector<uint8_t>& data,
+                            double timestamp) override;
+
+  // base::SystemMonitor::DevicesChangedObserver overrides:
+  void OnDevicesChanged(base::SystemMonitor::DeviceType device_type) override;
+
+ private:
+  class InPort;
+  class OutPort;
+
+  // Posts a task to TaskRunner, and ensures that the instance keeps alive while
+  // the task is running.
+  void PostTask(const base::Closure&);
+  void PostDelayedTask(const base::Closure&, base::TimeDelta delay);
+
+  // Initializes instance asynchronously on TaskRunner.
+  void InitializeOnTaskRunner();
+
+  // Updates device lists on TaskRunner.
+  // Returns true if device lists were changed.
+  void UpdateDeviceListOnTaskRunner();
+
+  // Sends MIDI data on TaskRunner.
+  void SendOnTaskRunner(MidiManagerClient* client,
+                        uint32_t port_index,
+                        const std::vector<uint8_t>& data);
+
+  // Holds an unique instance ID.
+  int instance_id_;
+
+  // Keeps a TaskRunner for the I/O thread.
+  scoped_refptr<base::SingleThreadTaskRunner> thread_runner_;
+
+  // Following members should be accessed only on TaskRunner.
+
+  // Holds all MIDI input or output ports connected once.
+  std::vector<std::unique_ptr<InPort>> input_ports_;
+  std::vector<std::unique_ptr<OutPort>> output_ports_;
+
+  DISALLOW_COPY_AND_ASSIGN(DynamicallyInitializedMidiManagerWin);
+};
+
+}  // namespace midi
+
+#endif  // MEDIA_MIDI_DYNAMICALLY_INITIALIZED_MIDI_MANAGER_WIN_H_