Clean up of url data manager classes in content: move URLDataSourceImpl to its own file, move all t…

content/browser/webui/url_data_source_impl.h

+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CONTENT_BROWSER_WEBUI_URL_DATA_SOURCE_IMPL_H_
+#define CONTENT_BROWSER_WEBUI_URL_DATA_SOURCE_IMPL_H_
+
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/sequenced_task_runner_helpers.h"
+#include "content/browser/webui/url_data_manager.h"
+#include "content/common/content_export.h"
+
+namespace base {
+class RefCountedMemory;
+}
+
+namespace content {
+class URLDataManagerBackend;
+class URLDataSource;
+class URLDataSourceImpl;
+
+// Trait used to handle deleting a URLDataSource. Deletion happens on the UI
+// thread.
+//
+// Implementation note: the normal shutdown sequence is for the UI loop to
+// stop pumping events then the IO loop and thread are stopped. When the
+// URLDataSources are no longer referenced (which happens when IO thread stops)
+// they get added to the UI message loop for deletion. But because the UI loop
+// has stopped by the time this happens the URLDataSources would be leaked.
+//
+// To make sure URLDataSources are properly deleted URLDataManager manages
+// deletion of the URLDataSources.  When a URLDataSource is no longer referenced
+// it is added to |data_sources_| and a task is posted to the UI thread to
+// handle the actual deletion. During shutdown |DeleteDataSources| is invoked so
+// that all pending URLDataSources are properly deleted.
+struct DeleteURLDataSource {
+  static void Destruct(const URLDataSourceImpl* data_source) {
+    URLDataManager::DeleteDataSource(data_source);
+  }
+};
+
+// A URLDataSource is an object that can answer requests for data
+// asynchronously. URLDataSources are collectively owned with refcounting smart
+// pointers and should never be deleted on the IO thread, since their calls
+// are handled almost always on the UI thread and there's a possibility of a
+// data race.  The |DeleteDataSource| trait above is used to enforce this.
+class URLDataSourceImpl : public base::RefCountedThreadSafe<
+    URLDataSourceImpl, DeleteURLDataSource> {
+ public:
+  // See source_name_ below for docs on that parameter. Takes ownership of
+  // |source|.
+  URLDataSourceImpl(const std::string& source_name,
+                    URLDataSource* source);
+
+  // Report that a request has resulted in the data |bytes|.
+  // If the request can't be satisfied, pass NULL for |bytes| to indicate
+  // the request is over.
+  virtual void SendResponse(int request_id, base::RefCountedMemory* bytes);
+
+  const std::string& source_name() const { return source_name_; }
+  URLDataSource* source() const { return source_.get(); }
+
+ protected:
+  virtual ~URLDataSourceImpl();
+
+ private:
+  friend class URLDataManager;
+  friend class URLDataManagerBackend;
+  friend class base::DeleteHelper<URLDataSourceImpl>;
+
+  // SendResponse invokes this on the IO thread. Notifies the backend to
+  // handle the actual work of sending the data.
+  virtual void SendResponseOnIOThread(
+      int request_id,
+      scoped_refptr<base::RefCountedMemory> bytes);
+
+  // The name of this source.
+  // E.g., for favicons, this could be "favicon", which results in paths for
+  // specific resources like "favicon/34" getting sent to this source.
+  const std::string source_name_;
+
+  // This field is set and maintained by URLDataManagerBackend. It is set when
+  // the DataSource is added, and unset if the DataSource is removed. A
+  // DataSource can be removed in two ways: the URLDataManagerBackend is
+  // deleted, or another DataSource is registered with the same name. backend_
+  // should only be accessed on the IO thread. This reference can't be via a
+  // scoped_refptr else there would be a cycle between the backend and data
+  // source.
+  URLDataManagerBackend* backend_;
+
+  scoped_ptr<URLDataSource> source_;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_WEBUI_URL_DATA_SOURCE_IMPL_H_