components/browser_context_keyed_service/refcounted_browser_context_keyed_service.h

   1 // Copyright (c) 2012 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_BROWSER_CONTEXT_KEYED_SERVICE_REFCOUNTED_BROWSER_CONTEXT_KEYED_SERVICE_H_
   6 #define COMPONENTS_BROWSER_CONTEXT_KEYED_SERVICE_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/browser_context_keyed_service/browser_context_keyed_service_export.h"
  11 #include "content/public/browser/browser_thread.h"
  12
  13 class RefcountedBrowserContextKeyedService;
  14
  15 namespace impl {
  16
  17 struct BROWSER_CONTEXT_KEYED_SERVICE_EXPORT
  18     RefcountedBrowserContextKeyedServiceTraits {
  19   static void Destruct(const RefcountedBrowserContextKeyedService* obj);
  20 };
  21
  22 }  // namespace impl
  23
  24 // Base class for refcounted objects that hang off the BrowserContext.
  25 //
  26 // The two pass shutdown described in BrowserContextKeyedService works a bit
  27 // differently because there could be outstanding references on other
  28 // threads. ShutdownOnUIThread() will be called on the UI thread, and then the
  29 // destructor will run when the last reference is dropped, which may or may not
  30 // be after the corresponding BrowserContext has been destroyed.
  31 //
  32 // Optionally, if you initialize your service with the constructor that takes a
  33 // thread ID, your service will be deleted on that thread. We can't use
  34 // content::DeleteOnThread<> directly because
  35 // RefcountedBrowserContextKeyedService must be one type that
  36 // RefcountedBrowserContextKeyedServiceFactory can use.
  37 class BROWSER_CONTEXT_KEYED_SERVICE_EXPORT RefcountedBrowserContextKeyedService
  38     : public base::RefCountedThreadSafe<
  39           RefcountedBrowserContextKeyedService,
  40           impl::RefcountedBrowserContextKeyedServiceTraits> {
  41  public:
  42   // Unlike BrowserContextKeyedService, ShutdownOnUI is not optional. You must
  43   // do something to drop references during the first pass Shutdown() because
  44   // this is the only point where you are guaranteed that something is running
  45   // on the UI thread. The PKSF framework will ensure that this is only called
  46   // on the UI thread; you do not need to check for that yourself.
  47   virtual void ShutdownOnUIThread() = 0;
  48
  49  protected:
  50   // If your service does not need to be deleted on a specific thread, use the
  51   // default constructor.
  52   RefcountedBrowserContextKeyedService();
  53
  54   // If you need your service to be deleted on a specific thread (for example,
  55   // you're converting a service that used content::DeleteOnThread<IO>), then
  56   // use this constructor with the ID of the thread.
  57   explicit RefcountedBrowserContextKeyedService(
  58       const content::BrowserThread::ID thread_id);
  59
  60   // The second pass destruction can happen anywhere unless you specify which
  61   // thread this service must be destroyed on by using the second constructor.
  62   virtual ~RefcountedBrowserContextKeyedService();
  63
  64  private:
  65   friend struct impl::RefcountedBrowserContextKeyedServiceTraits;
  66   friend class base::DeleteHelper<RefcountedBrowserContextKeyedService>;
  67   friend class base::RefCountedThreadSafe<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_BROWSER_CONTEXT_KEYED_SERVICE_REFCOUNTED_BROWSER_CONTEXT_KEYED_SERVICE_H_