components/keyed_service/content/refcounted_browser_context_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_CONTENT_REFCOUNTED_BROWSER_CONTEXT_KEYED_SERVICE_H_
   6 #define COMPONENTS_KEYED_SERVICE_CONTENT_REFCOUNTED_BROWSER_CONTEXT_KEYED_SERVICE_H_
   7
   8 #include "base/memory/ref_counted.h"
   9 #include "base/sequenced_task_runner_helpers.h"
  10 #include "components/keyed_service/core/keyed_service_export.h"
  11 #include "content/public/browser/browser_thread.h"
  12
  13 class RefcountedBrowserContextKeyedService;
  14
  15 namespace impl {
  16
  17 struct KEYED_SERVICE_EXPORT RefcountedBrowserContextKeyedServiceTraits {
  18   static void Destruct(const RefcountedBrowserContextKeyedService* 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 // thread ID, your service will be deleted on that thread. We can't use
  33 // content::DeleteOnThread<> directly because
  34 // RefcountedBrowserContextKeyedService must be one type that
  35 // RefcountedBrowserContextKeyedServiceFactory can use.
  36 class KEYED_SERVICE_EXPORT RefcountedBrowserContextKeyedService
  37     : public base::RefCountedThreadSafe<
  38           RefcountedBrowserContextKeyedService,
  39           impl::RefcountedBrowserContextKeyedServiceTraits> {
  40  public:
  41   // Unlike KeyedService, ShutdownOnUI is not optional. You must do something
  42   // to drop references during the first pass Shutdown() because this is the
  43   // only point where you are guaranteed that something is running on the UI
  44   // thread. The PKSF framework will ensure that this is only called on the UI
  45   // thread; you do not need to check for that yourself.
  46   virtual void ShutdownOnUIThread() = 0;
  47
  48  protected:
  49   // If your service does not need to be deleted on a specific thread, use the
  50   // default constructor.
  51   RefcountedBrowserContextKeyedService();
  52
  53   // If you need your service to be deleted on a specific thread (for example,
  54   // you're converting a service that used content::DeleteOnThread<IO>), then
  55   // use this constructor with the ID of the thread.
  56   explicit RefcountedBrowserContextKeyedService(
  57       const content::BrowserThread::ID thread_id);
  58
  59   // The second pass destruction can happen anywhere unless you specify which
  60   // thread this service must be destroyed on by using the second constructor.
  61   virtual ~RefcountedBrowserContextKeyedService();
  62
  63  private:
  64   friend struct impl::RefcountedBrowserContextKeyedServiceTraits;
  65   friend class base::DeleteHelper<RefcountedBrowserContextKeyedService>;
  66   friend class base::RefCountedThreadSafe<
  67       RefcountedBrowserContextKeyedService,
  68       impl::RefcountedBrowserContextKeyedServiceTraits>;
  69
  70   // Do we have to delete this object on a specific thread?
  71   bool requires_destruction_on_thread_;
  72   content::BrowserThread::ID thread_id_;
  73 };
  74
  75 #endif  // COMPONENTS_KEYED_SERVICE_CONTENT_REFCOUNTED_BROWSER_CONTEXT_KEYED_SERVICE_H_