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

net/url_request/request_throttler_entry.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_URL_REQUEST_REQUEST_THROTTLER_ENTRY_H_
+#define NET_URL_REQUEST_REQUEST_THROTTLER_ENTRY_H_
+
+#include "net/url_request/request_throttler_entry_interface.h"
+
+#include <queue>
+#include <string>
+
+#include "base/lock.h"
+
+// RequestThrottlerEntry represents an entry of RequestThrottlerManager.
+// It analyzes requests of a specific URL over some period of time, in order to
+// deduce the back-off time for every request.
+// The back-off algorithm consists of two parts. Firstly, exponential back-off
+// is used when receiving 5XX server errors or malformed response bodies.
+// The exponential back-off rule is enforced by URLRequestHttpJob. Any request
+// sent during the back-off period will be cancelled. Secondly, a sliding window

[Jói, 2010/11/12 00:12:08]

Secondly, a sliding... -> suggest replacement paragraph (and starting it as its
own paragraph):

A sliding window is used to count recent requests to a given destination and
provide guidance (to the application level only) on whether too many requests
have been sent and when a good time to send the next one would be. This is never
used to deny requests at the network level.

[yzshen, 2010/11/12 02:05:46]

Done.

+// is used to avoid too many send events in a short period of time.
+class RequestThrottlerEntry : public RequestThrottlerEntryInterface {
+ public:
+  // Sliding window period.
+  static const int kDefaultSlidingWindowPeriodMs;
+
+  // Maximum number of requests allowed in sliding window period.
+  static const int kDefaultMaxSendThreshold;
+
+  // Initial delay for exponential back-off.
+  static const int kDefaultInitialBackoffMs;
+
+  // Additional constant to adjust back-off.
+  static const int kDefaultAdditionalConstantMs;
+
+  // Factor by which the waiting time will be multiplied.
+  static const double kDefaultMultiplyFactor;
+
+  // Fuzzing percentage. ex: 10% will spread requests randomly
+  // between 90%-100% of the calculated time.
+  static const double kDefaultJitterFactor;
+
+  // Maximum amount of time we are willing to delay our request.
+  static const int kDefaultMaximumBackoffMs;
+
+  // Time after which the entry is considered outdated.
+  static const int kDefaultEntryLifetimeMs;
+
+  // Name of the header that servers can use to ask clients to delay their next
+  // request. ex: "X-Retry-After"
+  static const char kRetryHeaderName[];
+
+  RequestThrottlerEntry();
+
+  // The life span of instances created with this constructor is set to
+  // infinite.
+  RequestThrottlerEntry(int sliding_window_period_ms,
+                        int max_send_threshold,
+                        int initial_backoff_ms,
+                        int additional_constant_ms,
+                        double multiply_factor,
+                        double jitter_factor,
+                        int maximum_backoff_ms);
+
+  // Implementation of RequestThrottlerEntryInterface.
+  virtual bool IsDuringExponentialBackoff() const;
+  virtual int64 GetRecommendedDelayForNextRequest();
+  virtual void UpdateWithResponse(
+      const RequestThrottlerHeaderInterface* response);
+
+  // Used by the manager, returns true if the entry needs to be garbage
+  // collected.
+  bool IsEntryOutdated() const;
+
+  // Used by the manager, enables the manager to flag the last successful
+  // request as a failure.
+  void ReceivedContentWasMalformed();
+
+ protected:
+  // This struct is used to save the state of the entry each time we are updated
+  // with a response header so we can regenerate it if we are informed that one
+  // of our bodies was malformed.
+  struct OldValues {
+    base::TimeTicks exponential_backoff_release_time;
+    int failure_count;
+  };
+
+  virtual ~RequestThrottlerEntry();
+
+  void Initialize();
+
+  // Calculates the release time for exponential back-off.
+  base::TimeTicks CalculateExponentialBackoffReleaseTime();
+
+  // Equivalent to TimeTicks::Now(), virtual to be mockable for testing purpose.
+  virtual base::TimeTicks GetTimeNow() const;
+
+  // Used internally to increase release time following a retry-after header.
+  void HandleCustomRetryAfter(const std::string& header_value);
+
+  // Saves the state of the object to be able to regenerate it.
+  // Must be informed of the state of the response.
+  void SaveState();
+
+  // Timestamp calculated by the exponential back-off algorithm at which we are
+  // allowed to start sending requests again.
+  base::TimeTicks exponential_backoff_release_time_;
+
+  // Number of times we encounter server errors or malformed response bodies.
+  int failure_count_;
+
+  // Set to true if we are currently tracking requests with server errors or
+  // malformed response bodies, in order to calculate the exponential back-off
+  // release time.
+  bool tracking_exponential_backoff_;
+
+  OldValues old_values_;
+
+  // Timestamp calculated by the sliding window algorithm at which we are
+  // allowed to start sending requests again.
+  base::TimeTicks sliding_window_release_time_;
+
+  // A list of the recent send events. We use them to decide whether there are
+  // too many requests sent in sliding window.
+  std::queue<base::TimeTicks> send_log_;
+
+  const int sliding_window_period_ms_;
+  const int max_send_threshold_;
+  const int initial_backoff_ms_;
+  const int additional_constant_ms_;
+  const double multiply_factor_;
+  const double jitter_factor_;
+  const int maximum_backoff_ms_;
+  // Set to -1 if the entry never expires.
+  const int entry_lifetime_ms_;
+
+  // Lock to protect the non-static data members.
+  mutable Lock lock_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(RequestThrottlerEntry);
+};
+
+#endif  // NET_URL_REQUEST_REQUEST_THROTTLER_ENTRY_H_