components/keyed_service/core/keyed_service_shutdown_notifier.h

   1 // Copyright 2015 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef COMPONENTS_KEYED_SERVICE_CORE_KEYED_SERVICE_SHUTDOWN_NOTIFIER_H_
   6 #define COMPONENTS_KEYED_SERVICE_CORE_KEYED_SERVICE_SHUTDOWN_NOTIFIER_H_
   7
   8 #include "base/callback_list.h"
   9 #include "components/keyed_service/core/keyed_service.h"
  10
  11 // This is a helper class for objects that depend on one or more keyed services,
  12 // but which cannot be keyed services themselves, for example because they don't
  13 // correspond 1:1 to a context, or because they have a different lifetime.
  14 //
  15 // To use this class, add a factory class and declare the dependencies there.
  16 // This class (being a KeyedService itself) will be shut down before its
  17 // dependencies and notify its observers.
  18 class KEYED_SERVICE_EXPORT KeyedServiceShutdownNotifier : public KeyedService {
  19  public:
  20   using Subscription = base::CallbackList<void()>::Subscription;
  21
  22   KeyedServiceShutdownNotifier();
  23   ~KeyedServiceShutdownNotifier() override;
  24
  25   // Subscribe for a notification when the keyed services this object depends on
  26   // (as defined by its factory) are shut down. The subscription object can be
  27   // destroyed to unsubscribe.
  28   scoped_ptr<Subscription> Subscribe(const base::Closure& callback);
  29
  30  private:
  31   // KeyedService implementation:
  32   void Shutdown() override;
  33
  34   base::CallbackList<void()> callback_list_;
  35
  36   DISALLOW_COPY_AND_ASSIGN(KeyedServiceShutdownNotifier);
  37 };
  38
  39 #endif  // COMPONENTS_KEYED_SERVICE_CORE_KEYED_SERVICE_SHUTDOWN_NOTIFIER_H_