Implement exponential back-off mechanism and enforce it at the URLRequestHttpJob level.

net/request_throttler/request_throttler_manager.h

+// Copyright (c) 2010 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 NET_REQUEST_THROTTLER_REQUEST_THROTTLER_MANAGER_H_
+#define NET_REQUEST_THROTTLER_REQUEST_THROTTLER_MANAGER_H_
+
+#include <map>
+#include <string>
+
+#include "base/lock.h"
+#include "base/scoped_ptr.h"
+#include "base/singleton.h"
+#include "googleurl/src/gurl.h"
+#include "net/request_throttler/request_throttler_entry.h"
+
+// Class that registers a request throttler entry for each URL being accessed in
+// order to supervise traffic. URL requests for HTTP contents should register
+// their URLs in this request throttler manager on each request.
+class RequestThrottlerManager {
+ public:
+  // Must be called for every request, returns the request throttler entry
+  // associated with the URL. The caller must inform this entry of some events.
+  // Please refer to request_throttler_entry.h for further informations.
+  scoped_refptr<RequestThrottlerEntryInterface> RegisterRequestUrl(
+      const GURL& url);
+
+  // This method is used by higher level modules which can notify this class if
+  // the response they received was malformed. It is useful because
+  // in the case where the response header returned 200 response code but had
+  // a malformed content body we will categorize it as a success and so we
+  // defer this decision to the module that had requested the resource.
+  void NotifyRequestBodyWasMalformed(const GURL& url);
+
+  // Registers a new entry in this service and overrides the existing entry (if
+  // any) for the URL.
+  void OverrideEntry(const GURL& url,
+                     const scoped_refptr<RequestThrottlerEntry>& entry);
+
+  // Explicitly erases an entry.
+  // This is useful to remove those entries which have got infinite lifetime and
+  // thus won't be garbage collected.
+  void EraseEntry(const GURL& url);
+
+ protected:
+  RequestThrottlerManager();
+  virtual ~RequestThrottlerManager();
+
+  // Method that allows us to transform a URL into an ID that can be used in our
+  // map. Resulting IDs will be lowercase and be missing both the query string
+  // and fragment.
+  std::string GetIdFromUrl(const GURL& url);
+
+  // Method that ensures the map gets cleaned from time to time. The period at
+  // which garbage collecting happens is adjustable with the
+  // kRequestBetweenCollecting constant.
+  void GarbageCollectEntriesIfNecessary();
+  // Method that does the actual work of garbage collecting.
+  void GarbageCollectEntries();
+
+  // From each URL we generate an ID composed of the host and path
+  // that allows us to uniquely map an entry to it.
+  typedef std::map<std::string, scoped_refptr<RequestThrottlerEntry> >
+      UrlEntryMap;
+
+  friend struct DefaultSingletonTraits<RequestThrottlerManager>;
+
+  // Map that contains a list of URL ID and their matching
+  // RequestThrottlerEntry.
+  UrlEntryMap url_entries_;
+
+  // Lock to protect those non-static data members.
+  Lock lock_;
+
+ private:
+  // Maximum number of entries that we are willing to collect in our map.
+  static const unsigned int kMaximumNumberOfEntries;
+  // Number of requests that will be made between garbage collection.
+  static const unsigned int kRequestsBetweenCollecting;
+
+  // This keeps track of how many requests have been made. Used with
+  // GarbageCollectEntries.
+  unsigned int requests_since_last_gc_;
+
+  DISALLOW_COPY_AND_ASSIGN(RequestThrottlerManager);
+};
+
+#endif  // NET_REQUEST_THROTTLER_REQUEST_THROTTLER_MANAGER_H_