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.
NON_EXPORTED_BASE(public base::NonThreadSafe)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_
116