content/browser/webui/url_data_source_impl.h

   1 // Copyright (c) 2013 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 CONTENT_BROWSER_WEBUI_URL_DATA_SOURCE_IMPL_H_
   6 #define CONTENT_BROWSER_WEBUI_URL_DATA_SOURCE_IMPL_H_
   7
   8 #include "base/memory/ref_counted.h"
   9 #include "base/memory/scoped_ptr.h"
  10 #include "base/sequenced_task_runner_helpers.h"
  11 #include "content/browser/webui/url_data_manager.h"
  12 #include "content/common/content_export.h"
  13
  14 namespace base {
  15 class RefCountedMemory;
  16 }
  17
  18 namespace content {
  19 class URLDataManagerBackend;
  20 class URLDataSource;
  21 class URLDataSourceImpl;
  22
  23 // Trait used to handle deleting a URLDataSource. Deletion happens on the UI
  24 // thread.
  25 //
  26 // Implementation note: the normal shutdown sequence is for the UI loop to
  27 // stop pumping events then the IO loop and thread are stopped. When the
  28 // URLDataSources are no longer referenced (which happens when IO thread stops)
  29 // they get added to the UI message loop for deletion. But because the UI loop
  30 // has stopped by the time this happens the URLDataSources would be leaked.
  31 //
  32 // To make sure URLDataSources are properly deleted URLDataManager manages
  33 // deletion of the URLDataSources.  When a URLDataSource is no longer referenced
  34 // it is added to |data_sources_| and a task is posted to the UI thread to
  35 // handle the actual deletion. During shutdown |DeleteDataSources| is invoked so
  36 // that all pending URLDataSources are properly deleted.
  37 struct DeleteURLDataSource {
  38   static void Destruct(const URLDataSourceImpl* data_source) {
  39     URLDataManager::DeleteDataSource(data_source);
  40   }
  41 };
  42
  43 // A URLDataSource is an object that can answer requests for data
  44 // asynchronously. URLDataSources are collectively owned with refcounting smart
  45 // pointers and should never be deleted on the IO thread, since their calls
  46 // are handled almost always on the UI thread and there's a possibility of a
  47 // data race.  The |DeleteDataSource| trait above is used to enforce this.
  48 class URLDataSourceImpl : public base::RefCountedThreadSafe<
  49     URLDataSourceImpl, DeleteURLDataSource> {
  50  public:
  51   // See source_name_ below for docs on that parameter. Takes ownership of
  52   // |source|.
  53   URLDataSourceImpl(const std::string& source_name,
  54                     URLDataSource* source);
  55
  56   // Report that a request has resulted in the data |bytes|.
  57   // If the request can't be satisfied, pass NULL for |bytes| to indicate
  58   // the request is over.
  59   virtual void SendResponse(int request_id, base::RefCountedMemory* bytes);
  60
  61   const std::string& source_name() const { return source_name_; }
  62   URLDataSource* source() const { return source_.get(); }
  63
  64  protected:
  65   virtual ~URLDataSourceImpl();
  66
  67  private:
  68   friend class URLDataManager;
  69   friend class URLDataManagerBackend;
  70   friend class base::DeleteHelper<URLDataSourceImpl>;
  71
  72   // SendResponse invokes this on the IO thread. Notifies the backend to
  73   // handle the actual work of sending the data.
  74   virtual void SendResponseOnIOThread(
  75       int request_id,
  76       scoped_refptr<base::RefCountedMemory> bytes);
  77
  78   // The name of this source.
  79   // E.g., for favicons, this could be "favicon", which results in paths for
  80   // specific resources like "favicon/34" getting sent to this source.
  81   const std::string source_name_;
  82
  83   // This field is set and maintained by URLDataManagerBackend. It is set when
  84   // the DataSource is added, and unset if the DataSource is removed. A
  85   // DataSource can be removed in two ways: the URLDataManagerBackend is
  86   // deleted, or another DataSource is registered with the same name. backend_
  87   // should only be accessed on the IO thread. This reference can't be via a
  88   // scoped_refptr else there would be a cycle between the backend and data
  89   // source.
  90   URLDataManagerBackend* backend_;
  91
  92   scoped_ptr<URLDataSource> source_;
  93 };
  94
  95 }  // namespace content
  96
  97 #endif  // CONTENT_BROWSER_WEBUI_URL_DATA_SOURCE_IMPL_H_