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

chrome/common/net/url_fetcher_protect.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.
-//
-// This file implements backoff in the suggest system so that we don't
-// DOS the Suggest servers when using URLFetcher.
-
-#ifndef CHROME_COMMON_NET_URL_FETCHER_PROTECT_H_
-#define CHROME_COMMON_NET_URL_FETCHER_PROTECT_H_
-#pragma once
-
-#include <map>
-#include <queue>
-#include <string>
-
-#include "base/lock.h"
-#include "base/scoped_ptr.h"
-#include "base/time.h"
-
-
-// This class is used to manage one service's rate protection. It maintains
-// a queue of connection successes and failures and analyzes the requests
-// over some period of time, in order to deduce the backoff time of every
-// request.
-// The backoff algorithm consists of two parts. Firstly, avoid too many
-// send events in a sliding window. That will prevent traffic overload.
-// Secondly, exponential backoff is used when receiving an error message
-// from server. Exponential backoff period is calculated using the following
-// formula:
-//
-//             initial backoff time      (the first time to receive error)
-//  backoff =  k * current_backoff + c   (the second, third, ... error)
-//             maximum backoff time      (when backoff > maximum backoff time)
-//
-// where |k| is the multiplier, and |c| is the constant factor.
-class URLFetcherProtectEntry {
- public:
-  enum EventType {
-    SEND,      // request will be sent out
-    SUCCESS,   // successful response
-    FAILURE    // no response or error
-  };
-
-  URLFetcherProtectEntry();
-  URLFetcherProtectEntry(int sliding_window_period, int max_send_threshold,
-                         int max_retries, int initial_timeout,
-                         double multiplier, int constant_factor,
-                         int maximum_timeout);
-
-
-  virtual ~URLFetcherProtectEntry();
-
-  // When a connection event happens, log it to the queue, and recalculate
-  // the timeout period. It returns the backoff time, in milliseconds, that
-  // indicates to the sender how long should it wait before sending the request.
-  // If the request is allowed to be sent immediately, the backoff time is 0.
-  int64 UpdateBackoff(EventType event_type);
-
-  // Returns the max retries allowed.
-  int max_retries() const {
-    return max_retries_;
-  }
-
-  // Sets the max retries.
-  void SetMaxRetries(int max_retries) {
-    max_retries_ = max_retries;
-  }
-
- private:
-  // When a request comes, calculate the release time for it.
-  // Returns the backoff time before sending.
-  base::TimeDelta AntiOverload();
-  // Resets backoff when service is ok.
-  // Returns the backoff time before sending.
-  base::TimeDelta ResetBackoff();
-  // Calculates new backoff when encountering a failure.
-  // Returns the backoff time before sending.
-  base::TimeDelta IncreaseBackoff();
-
-  // Default parameters.  Time is in milliseconds.
-  static const int kDefaultSlidingWindowPeriod;
-  static const int kDefaultMaxSendThreshold;
-  static const int kDefaultMaxRetries;
-  static const int kDefaultInitialTimeout;
-  static const double kDefaultMultiplier;
-  static const int kDefaultConstantFactor;
-  static const int kDefaultMaximumTimeout;
-
-  // time to consider events when checking backoff
-  int sliding_window_period_;
-
-  // maximum number of requests allowed in sliding window period
-  int max_send_threshold_;
-  // maximum retris allowed
-  int max_retries_;
-
-  // initial timeout on first failure
-  int initial_timeout_;
-  // factor by which to multiply on exponential backoff (e.g., 2.0)
-  double multiplier_;
-  // constant time term to add to each attempt
-  int constant_factor_;
-  // maximum amount of time between requests
-  int maximum_timeout_;
-
-  // current exponential backoff period
-  int timeout_period_;
-  // time that protection is scheduled to end
-  base::TimeTicks release_time_;
-
-  // Sets up a lock to ensure thread safe.
-  Lock lock_;
-
-  // A list of the recent send events. We ues them to decide whether
-  // there are too many requests sent in sliding window.
-  std::queue<base::TimeTicks> send_log_;
-
-  DISALLOW_COPY_AND_ASSIGN(URLFetcherProtectEntry);
-};
-
-
-// This singleton class is used to manage all protect entries.
-// Now we use the host name as service id.
-class URLFetcherProtectManager {
- public:
-  ~URLFetcherProtectManager();
-
-  // Returns the global instance of this class.
-  static URLFetcherProtectManager* GetInstance();
-
-  // Registers a new entry in this service. If the entry already exists,
-  // just returns it. Ownership of the return object remains with the manager.
-  URLFetcherProtectEntry* Register(const std::string& id);
-  // Always registers the entry even when it exists; any existing entry for this
-  // id will be deleted and existing references to it will become invalid.
-  // Ownership of the return object remains with the manager.
-  URLFetcherProtectEntry* Register(const std::string& id,
-                                   URLFetcherProtectEntry* entry);
-
- private:
-  URLFetcherProtectManager();
-
-  typedef std::map<const std::string, URLFetcherProtectEntry*> ProtectService;
-
-  static Lock lock_;
-  static scoped_ptr<URLFetcherProtectManager> protect_manager_;
-  ProtectService services_;
-
-  DISALLOW_COPY_AND_ASSIGN(URLFetcherProtectManager);
-};
-
-#endif  // CHROME_COMMON_NET_URL_FETCHER_PROTECT_H_