net/base/backoff_entry.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef NET_BASE_BACKOFF_ENTRY_H_
   6 #define NET_BASE_BACKOFF_ENTRY_H_
   7
   8 #include "base/threading/non_thread_safe.h"
   9 #include "base/time/time.h"
  10 #include "net/base/net_export.h"
  11
  12 namespace net {
  13
  14 // Provides the core logic needed for randomized exponential back-off
  15 // on requests to a given resource, given a back-off policy.
  16 //
  17 // This utility class knows nothing about network specifics; it is
  18 // intended for reuse in various networking scenarios.
  19 class NET_EXPORT BackoffEntry : NON_EXPORTED_BASE(public base::NonThreadSafe) {
  20  public:
  21   // The set of parameters that define a back-off policy.
  22   struct Policy {
  23     // Number of initial errors (in sequence) to ignore before applying
  24     // exponential back-off rules.
  25     int num_errors_to_ignore;
  26
  27     // Initial delay.  The interpretation of this value depends on
  28     // always_use_initial_delay.  It's either how long we wait between
  29     // requests before backoff starts, or how much we delay the first request
  30     // after backoff starts.
  31     int initial_delay_ms;
  32
  33     // Factor by which the waiting time will be multiplied.
  34     double multiply_factor;
  35
  36     // Fuzzing percentage. ex: 10% will spread requests randomly
  37     // between 90%-100% of the calculated time.
  38     double jitter_factor;
  39
  40     // Maximum amount of time we are willing to delay our request, -1
  41     // for no maximum.
  42     int64 maximum_backoff_ms;
  43
  44     // Time to keep an entry from being discarded even when it
  45     // has no significant state, -1 to never discard.
  46     int64 entry_lifetime_ms;
  47
  48     // If true, we always use a delay of initial_delay_ms, even before
  49     // we've seen num_errors_to_ignore errors.  Otherwise, initial_delay_ms
  50     // is the first delay once we start exponential backoff.
  51     //
  52     // So if we're ignoring 1 error, we'll see (N, N, Nm, Nm^2, ...) if true,
  53     // and (0, 0, N, Nm, ...) when false, where N is initial_backoff_ms and
  54     // m is multiply_factor, assuming we've already seen one success.
  55     bool always_use_initial_delay;
  56   };
  57
  58   // Lifetime of policy must enclose lifetime of BackoffEntry. The
  59   // pointer must be valid but is not dereferenced during construction.
  60   explicit BackoffEntry(const Policy* const policy);
  61   virtual ~BackoffEntry();
  62
  63   // Inform this item that a request for the network resource it is
  64   // tracking was made, and whether it failed or succeeded.
  65   void InformOfRequest(bool succeeded);
  66
  67   // Returns true if a request for the resource this item tracks should
  68   // be rejected at the present time due to exponential back-off policy.
  69   bool ShouldRejectRequest() const;
  70
  71   // Returns the absolute time after which this entry (given its present
  72   // state) will no longer reject requests.
  73   base::TimeTicks GetReleaseTime() const;
  74
  75   // Returns the time until a request can be sent.
  76   base::TimeDelta GetTimeUntilRelease() const;
  77
  78   // Causes this object reject requests until the specified absolute time.
  79   // This can be used to e.g. implement support for a Retry-After header.
  80   void SetCustomReleaseTime(const base::TimeTicks& release_time);
  81
  82   // Returns true if this object has no significant state (i.e. you could
  83   // just as well start with a fresh BackoffEntry object), and hasn't
  84   // had for Policy::entry_lifetime_ms.
  85   bool CanDiscard() const;
  86
  87   // Resets this entry to a fresh (as if just constructed) state.
  88   void Reset();
  89
  90   // Returns the failure count for this entry.
  91   int failure_count() const { return failure_count_; }
  92
  93  protected:
  94   // Equivalent to TimeTicks::Now(), virtual so unit tests can override.
  95   virtual base::TimeTicks ImplGetTimeNow() const;
  96
  97  private:
  98   // Calculates when requests should again be allowed through.
  99   base::TimeTicks CalculateReleaseTime() const;
 100
 101   // Timestamp calculated by the exponential back-off algorithm at which we are
 102   // allowed to start sending requests again.
 103   base::TimeTicks exponential_backoff_release_time_;
 104
 105   // Counts request errors; decremented on success.
 106   int failure_count_;
 107
 108   const Policy* const policy_;
 109
 110   DISALLOW_COPY_AND_ASSIGN(BackoffEntry);
 111 };
 112
 113 }  // namespace net
 114
 115 #endif  // NET_BASE_BACKOFF_ENTRY_H_