Implement ResourceQueue, an object that makes it easy to delay starting

chrome/browser/renderer_host/resource_queue.h

+// Copyright (c) 2009 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 CHROME_BROWSER_RENDERER_HOST_RESOURCE_QUEUE_H_
+#define CHROME_BROWSER_RENDERER_HOST_RESOURCE_QUEUE_H_
+
+#include <map>
+#include <set>
+
+#include "base/basictypes.h"
+
+class ResourceDispatcherHostRequestInfo;
+class URLRequest;
+struct GlobalRequestID;
+
+// Makes decisions about delaying or not each URLRequest in the queue.
+// All methods are called on the IO thread.
+class ResourceQueueDelegate {
+ public:
+  // Should return true if it wants the |request| to not be started at this
+  // point. To start the delayed request, ResourceQueue::StartDelayedRequest
+  // should be used.
+  virtual bool ShouldDelayRequest(
+      URLRequest* request,
+      const ResourceDispatcherHostRequestInfo& request_info,
+      const GlobalRequestID& request_id) = 0;
+
+  // Called just before ResourceQueue shutdown. After that, the delegate
+  // should not use the ResourceQueue.
+  virtual void WillShutdownResourceQueue() = 0;
+
+ protected:
+  virtual ~ResourceQueueDelegate();
+};
+
+// Makes it easy to delay starting URL requests until specified conditions are
+// met.
+class ResourceQueue {
+ public:
+  typedef std::set<ResourceQueueDelegate*> DelegateSet;
+
+  // UI THREAD ONLY ------------------------------------------------------------
+
+  // Construct the queue. You must initialize it using Initialize.
+  ResourceQueue();
+  ~ResourceQueue();
+
+  // Initialize the queue with set of delegates it should ask for each incoming
+  // request.
+  void Initialize(const DelegateSet& delegates);
+
+  // IO THREAD ONLY ------------------------------------------------------------
+
+  // Must be called before destroying the queue. No other methods can be called
+  // after that.
+  void Shutdown();
+
+  // Takes care to start the |request| after all delegates allow that. If no
+  // delegate demands delaying the request it will be started immediately.
+  void AddRequest(URLRequest* request,
+                  const ResourceDispatcherHostRequestInfo& request_info);
+
+  // Tells the queue that the URLRequest object associated with |request_id|
+  // is no longer valid.
+  void RemoveRequest(const GlobalRequestID& request_id);
+
+  // A delegate should call StartDelayedRequest when it wants to allow the
+  // request to start. If it was the last delegate that demanded the request
+  // to be delayed, the request will be started.
+  void StartDelayedRequest(ResourceQueueDelegate* delegate,
+                           const GlobalRequestID& request_id);
+
+ private:
+  typedef std::map<GlobalRequestID, URLRequest*> RequestMap;
+  typedef std::map<GlobalRequestID, DelegateSet> InterestedDelegatesMap;
+
+  // The registered delegates. Will not change after the queue has been
+  // initialized.
+  DelegateSet delegates_;
+
+  // Stores URLRequest objects associated with each GlobalRequestID. This helps
+  // decoupling the queue from ResourceDispatcherHost.
+  RequestMap requests_;
+
+  // Maps a GlobalRequestID to the set of delegates that want to prevent the
+  // associated request from starting yet.
+  InterestedDelegatesMap interested_delegates_;
+
+  // True when we are shutting down.
+  bool shutdown_;
+
+  DISALLOW_COPY_AND_ASSIGN(ResourceQueue);
+};
+
+#endif  // CHROME_BROWSER_RENDERER_HOST_RESOURCE_QUEUE_H_