chromium/content/browser/webui/url_data_source_impl.h

// Copyright 2013 The Chromium Authors
// 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 <memory>
#include <string>

#include "base/memory/ref_counted.h"
#include "base/memory/weak_ptr.h"
#include "base/task/sequenced_task_runner_helpers.h"
#include "content/browser/webui/url_data_manager.h"

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 { … };

// 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> { … };

}  // namespace content

#endif  // CONTENT_BROWSER_WEBUI_URL_DATA_SOURCE_IMPL_H_