flutter_desktop_messenger.h

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// Copyright 2013 The Flutter 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 FLUTTER_SHELL_PLATFORM_WINDOWS_FLUTTER_DESKTOP_MESSENGER_H_
#define FLUTTER_SHELL_PLATFORM_WINDOWS_FLUTTER_DESKTOP_MESSENGER_H_
 
#include <atomic>
#include <mutex>
 
#include "flutter/fml/macros.h"
#include "flutter/shell/platform/common/public/flutter_messenger.h"
 
namespace flutter {
 
class FlutterWindowsEngine;
 
/// A messenger object used to invoke platform messages.
///
/// On Windows, the message handler is essentially the |FlutterWindowsEngine|,
/// this allows a handle to the |FlutterWindowsEngine| that will become
/// invalidated if the |FlutterWindowsEngine| is destroyed.
class FlutterDesktopMessenger {
 public:
  FlutterDesktopMessenger() = default;
 
  /// Convert to FlutterDesktopMessengerRef.
  FlutterDesktopMessengerRef ToRef() {
    return reinterpret_cast<FlutterDesktopMessengerRef>(this);
  }
 
  /// Convert from FlutterDesktopMessengerRef.
  static FlutterDesktopMessenger* FromRef(FlutterDesktopMessengerRef ref) {
    return reinterpret_cast<FlutterDesktopMessenger*>(ref);
  }
 
  /// Getter for the engine field.
  flutter::FlutterWindowsEngine* GetEngine() const { return engine; }
 
  /// Setter for the engine field.
  /// Thread-safe.
  void SetEngine(flutter::FlutterWindowsEngine* arg_engine) {
    std::scoped_lock lock(mutex_);
    engine = arg_engine;
  }
 
  /// Increments the reference count.
  ///
  /// Thread-safe.
  FlutterDesktopMessenger* AddRef() {
    ref_count_.fetch_add(1);
    return this;
  }
 
  /// Decrements the reference count and deletes the object if the count has
  /// gone to zero.
  ///
  /// Thread-safe.
  void Release() {
    int32_t old_count = ref_count_.fetch_sub(1);
    if (old_count <= 1) {
      delete this;
    }
  }
 
  /// Returns the mutex associated with the |FlutterDesktopMessenger|.
  ///
  /// This mutex is used to synchronize reading or writing state inside the
  /// |FlutterDesktopMessenger| (ie |engine|).
  std::mutex& GetMutex() { return mutex_; }
 
 private:
  // The engine that owns this state object.
  flutter::FlutterWindowsEngine* engine = nullptr;
  std::mutex mutex_;
  std::atomic<int32_t> ref_count_ = 0;
 
  FML_DISALLOW_COPY_AND_ASSIGN(FlutterDesktopMessenger);
};
 
}  // namespace flutter
 
#endif  // FLUTTER_SHELL_PLATFORM_WINDOWS_FLUTTER_DESKTOP_MESSENGER_H_