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      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_
     98