Implement exponential back-off mechanism.

net/url_request/url_request_throttler_manager.h

Index: net/url_request/url_request_throttler_manager.h
diff --git a/net/url_request/url_request_throttler_manager.h b/net/url_request/url_request_throttler_manager.h
new file mode 100644
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+++ b/net/url_request/url_request_throttler_manager.h
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+// 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_URL_REQUEST_URL_REQUEST_THROTTLER_MANAGER_H_
+#define NET_URL_REQUEST_URL_REQUEST_THROTTLER_MANAGER_H_
+
+#include <map>
+#include <string>
+
+#include "base/basictypes.h"
+#include "base/scoped_ptr.h"
+#include "base/singleton.h"
+#include "googleurl/src/gurl.h"
+#include "net/url_request/url_request_throttler_entry.h"
+
+namespace net {
+
+// Class that registers URL request throttler entries for URLs being accessed in
+// order to supervise traffic. URL requests for HTTP contents should register
+// their URLs in this manager on each request.
+// URLRequestThrottlerManager maintains a map of URL IDs to URL request
+// throttler entries. It creates URL request throttler entries when new URLs are
+// registered, and does garbage collection from time to time in order to clean
+// out outdated entries. URL ID consists of lowercased scheme, host, port and
+// path. All URLs converted to the same ID will share the same entry.
+//
+// NOTE: All usage of the singleton object of this class should be on the same
+// thread.
+class URLRequestThrottlerManager {
+ public:
+  static URLRequestThrottlerManager* GetInstance();
+
+  // Must be called for every request, returns the URL request throttler entry
+  // associated with the URL. The caller must inform this entry of some events.
+  // Please refer to url_request_throttler_entry_interface.h for further
+  // informations.
+  scoped_refptr<URLRequestThrottlerEntryInterface> RegisterRequestUrl(
+      const GURL& url);
+
+  // Registers a new entry in this service and overrides the existing entry (if
+  // any) for the URL. The service will hold a reference to the entry.
+  // It is only used by unit tests.
+  void OverrideEntryForTests(const GURL& url, URLRequestThrottlerEntry* entry);
+
+  // Explicitly erases an entry.
+  // This is useful to remove those entries which have got infinite lifetime and
+  // thus won't be garbage collected.
+  // It is only used by unit tests.
+  void EraseEntryForTests(const GURL& url);
+
+ protected:
+  URLRequestThrottlerManager();
+  ~URLRequestThrottlerManager();
+
+  // Method that allows us to transform a URL into an ID that can be used in our
+  // map. Resulting IDs will be lowercase and consist of the scheme, host, port
+  // and path (without query string, fragment, etc.).
+  // If the URL is invalid, the invalid spec will be returned, without any
+  // transformation.
+  std::string GetIdFromUrl(const GURL& url) const;
+
+  // 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();
+
+  // Used by tests.
+  int GetNumberOfEntriesForTests() const { return url_entries_.size(); }
+
+ private:
+  friend struct DefaultSingletonTraits<URLRequestThrottlerManager>;
+
+  // From each URL we generate an ID composed of the scheme, host, port and path
+  // that allows us to uniquely map an entry to it.
+  typedef std::map<std::string, scoped_refptr<URLRequestThrottlerEntry> >
+      UrlEntryMap;
+
+  // 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;
+
+  // Map that contains a list of URL ID and their matching
+  // URLRequestThrottlerEntry.
+  UrlEntryMap url_entries_;
+
+  // This keeps track of how many requests have been made. Used with
+  // GarbageCollectEntries.
+  unsigned int requests_since_last_gc_;
+
+  mutable scoped_ptr<GURL::Replacements> url_id_replacements_;
+
+  DISALLOW_COPY_AND_ASSIGN(URLRequestThrottlerManager);
+};
+
+}  // namespace net
+
+#endif  // NET_URL_REQUEST_URL_REQUEST_THROTTLER_MANAGER_H_