components/keyed_service/core/refcounted_keyed_service.h

   1 // Copyright 2014 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_REFCOUNTED_KEYED_SERVICE_H_
   6 #define COMPONENTS_KEYED_SERVICE_CORE_REFCOUNTED_KEYED_SERVICE_H_
   7
   8 #include "base/memory/ref_counted.h"
   9 #include "base/sequenced_task_runner_helpers.h"
  10 #include "base/single_thread_task_runner.h"
  11 #include "components/keyed_service/core/keyed_service_export.h"
  12
  13 class RefcountedKeyedService;
  14
  15 namespace impl {
  16
  17 struct KEYED_SERVICE_EXPORT RefcountedKeyedServiceTraits {
  18   static void Destruct(const RefcountedKeyedService* obj);
  19 };
  20
  21 }  // namespace impl
  22
  23 // Base class for refcounted objects that hang off the BrowserContext.
  24 //
  25 // The two pass shutdown described in KeyedService works a bit differently
  26 // because there could be outstanding references on other threads.
  27 // ShutdownOnUIThread() will be called on the UI thread, and then the
  28 // destructor will run when the last reference is dropped, which may or may not
  29 // be after the corresponding BrowserContext has been destroyed.
  30 //
  31 // Optionally, if you initialize your service with the constructor that takes a
  32 // single thread task runner, your service will be deleted on that thread. We
  33 // can't use content::DeleteOnThread<> directly because RefcountedKeyedService
  34 // must not depend on //content.
  35 class KEYED_SERVICE_EXPORT RefcountedKeyedService
  36     : public base::RefCountedThreadSafe<RefcountedKeyedService,
  37                                         impl::RefcountedKeyedServiceTraits> {
  38  public:
  39   // Unlike KeyedService, ShutdownOnUI is not optional. You must do something
  40   // to drop references during the first pass Shutdown() because this is the
  41   // only point where you are guaranteed that something is running on the UI
  42   // thread. The PKSF framework will ensure that this is only called on the UI
  43   // thread; you do not need to check for that yourself.
  44   virtual void ShutdownOnUIThread() = 0;
  45
  46  protected:
  47   // If your service does not need to be deleted on a specific thread, use the
  48   // default constructor.
  49   RefcountedKeyedService();
  50
  51   // If you need your service to be deleted on a specific thread (for example,
  52   // you're converting a service that used content::DeleteOnThread<IO>), then
  53   // use this constructor with a reference to the SingleThreadTaskRunner (you
  54   // can get it from content::BrowserThread::GetMessageLoopProxyForThread).
  55   explicit RefcountedKeyedService(
  56       const scoped_refptr<base::SingleThreadTaskRunner>& task_runner);
  57
  58   // The second pass destruction can happen anywhere unless you specify which
  59   // thread this service must be destroyed on by using the second constructor.
  60   virtual ~RefcountedKeyedService();
  61
  62  private:
  63   friend struct impl::RefcountedKeyedServiceTraits;
  64   friend class base::DeleteHelper<RefcountedKeyedService>;
  65   friend class base::RefCountedThreadSafe<RefcountedKeyedService,
  66                                           impl::RefcountedKeyedServiceTraits>;
  67
  68   // Do we have to delete this object on a specific thread?
  69   scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
  70 };
  71
  72 #endif  // COMPONENTS_KEYED_SERVICE_CORE_REFCOUNTED_KEYED_SERVICE_H_