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/macros.h"
   9 #include "base/threading/non_thread_safe.h"
  10 #include "base/time/time.h"
  11 #include "net/base/net_export.h"
  12
  13 namespace base {
  14 class TickClock;
  15 }
  16
  17 namespace net {
  18
  19 // Provides the core logic needed for randomized exponential back-off
  20 // on requests to a given resource, given a back-off policy.
  21 //
  22 // This utility class knows nothing about network specifics; it is
  23 // intended for reuse in various networking scenarios.
  24 class NET_EXPORT BackoffEntry : NON_EXPORTED_BASE(public base::NonThreadSafe) {
  25  public:
  26   // The set of parameters that define a back-off policy. When modifying this,
  27   // increment SERIALIZATION_VERSION_NUMBER in backoff_entry_serializer.cc.
  28   struct Policy {
  29     // Number of initial errors (in sequence) to ignore before applying
  30     // exponential back-off rules.
  31     int num_errors_to_ignore;
  32
  33     // Initial delay.  The interpretation of this value depends on
  34     // always_use_initial_delay.  It's either how long we wait between
  35     // requests before backoff starts, or how much we delay the first request
  36     // after backoff starts.
  37     int initial_delay_ms;
  38
  39     // Factor by which the waiting time will be multiplied.
  40     double multiply_factor;
  41
  42     // Fuzzing percentage. ex: 10% will spread requests randomly
  43     // between 90%-100% of the calculated time.
  44     double jitter_factor;
  45
  46     // Maximum amount of time we are willing to delay our request, -1
  47     // for no maximum.
  48     int64 maximum_backoff_ms;
  49
  50     // Time to keep an entry from being discarded even when it
  51     // has no significant state, -1 to never discard.
  52     int64 entry_lifetime_ms;
  53
  54     // If true, we always use a delay of initial_delay_ms, even before
  55     // we've seen num_errors_to_ignore errors.  Otherwise, initial_delay_ms
  56     // is the first delay once we start exponential backoff.
  57     //
  58     // So if we're ignoring 1 error, we'll see (N, N, Nm, Nm^2, ...) if true,
  59     // and (0, 0, N, Nm, ...) when false, where N is initial_backoff_ms and
  60     // m is multiply_factor, assuming we've already seen one success.
  61     bool always_use_initial_delay;
  62   };
  63
  64   // Lifetime of policy must enclose lifetime of BackoffEntry. The
  65   // pointer must be valid but is not dereferenced during construction.
  66   explicit BackoffEntry(const Policy* policy);
  67   // Lifetime of policy and clock must enclose lifetime of BackoffEntry.
  68   // |policy| pointer must be valid but isn't dereferenced during construction.
  69   // |clock| pointer may be null.
  70   BackoffEntry(const Policy* policy, base::TickClock* clock);
  71   virtual ~BackoffEntry();
  72
  73   // Inform this item that a request for the network resource it is
  74   // tracking was made, and whether it failed or succeeded.
  75   void InformOfRequest(bool succeeded);
  76
  77   // Returns true if a request for the resource this item tracks should
  78   // be rejected at the present time due to exponential back-off policy.
  79   bool ShouldRejectRequest() const;
  80
  81   // Returns the absolute time after which this entry (given its present
  82   // state) will no longer reject requests.
  83   base::TimeTicks GetReleaseTime() const;
  84
  85   // Returns the time until a request can be sent (will be zero if the release
  86   // time is in the past).
  87   base::TimeDelta GetTimeUntilRelease() const;
  88
  89   // Converts |backoff_duration| to a release time, by adding it to
  90   // GetTimeTicksNow(), limited by maximum_backoff_ms.
  91   base::TimeTicks BackoffDurationToReleaseTime(
  92       base::TimeDelta backoff_duration) const;
  93
  94   // Causes this object reject requests until the specified absolute time.
  95   // This can be used to e.g. implement support for a Retry-After header.
  96   void SetCustomReleaseTime(const base::TimeTicks& release_time);
  97
  98   // Returns true if this object has no significant state (i.e. you could
  99   // just as well start with a fresh BackoffEntry object), and hasn't
 100   // had for Policy::entry_lifetime_ms.
 101   bool CanDiscard() const;
 102
 103   // Resets this entry to a fresh (as if just constructed) state.
 104   void Reset();
 105
 106   // Returns the failure count for this entry.
 107   int failure_count() const { return failure_count_; }
 108
 109   // Returns the TickClock passed in to the constructor. May be NULL.
 110   base::TickClock* tick_clock() const { return clock_; }
 111
 112  private:
 113   // Calculates when requests should again be allowed through.
 114   base::TimeTicks CalculateReleaseTime() const;
 115
 116   // Equivalent to TimeTicks::Now(), using clock_ if provided.
 117   base::TimeTicks GetTimeTicksNow() const;
 118
 119   // Timestamp calculated by the exponential back-off algorithm at which we are
 120   // allowed to start sending requests again.
 121   base::TimeTicks exponential_backoff_release_time_;
 122
 123   // Counts request errors; decremented on success.
 124   int failure_count_;
 125
 126   const Policy* const policy_;  // Not owned.
 127
 128   base::TickClock* const clock_;  // Not owned.
 129
 130   DISALLOW_COPY_AND_ASSIGN(BackoffEntry);
 131 };
 132
 133 }  // namespace net
 134
 135 #endif  // NET_BASE_BACKOFF_ENTRY_H_