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Backoff.h
1 /*
2  * This library is free software; you can redistribute it and/or
3  * modify it under the terms of the GNU Lesser General Public
4  * License as published by the Free Software Foundation; either
5  * version 2.1 of the License, or (at your option) any later version.
6  *
7  * This library is distributed in the hope that it will be useful,
8  * but WITHOUT ANY WARRANTY; without even the implied warranty of
9  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
10  * Lesser General Public License for more details.
11  *
12  * You should have received a copy of the GNU Lesser General Public
13  * License along with this library; if not, write to the Free Software
14  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
15  *
16  * Backoff.h
17  * Copyright (C) 2013 Simon Newton
18  */
19 
20 #ifndef INCLUDE_OLA_UTIL_BACKOFF_H_
21 #define INCLUDE_OLA_UTIL_BACKOFF_H_
22 
23 #include <math.h>
24 #include <ola/Clock.h>
25 #include <memory>
26 
27 namespace ola {
28 
34  public:
35  BackOffPolicy() {}
36  virtual ~BackOffPolicy() {}
37 
44  virtual TimeInterval BackOffTime(unsigned int failed_attempts) const = 0;
45 };
46 
47 
53  public:
54  explicit ConstantBackoffPolicy(const TimeInterval &duration)
55  : m_duration(duration) {
56  }
57 
58  TimeInterval BackOffTime(unsigned int) const {
59  return m_duration;
60  }
61 
62  private:
63  const TimeInterval m_duration;
64 };
65 
66 
74  public:
75  LinearBackoffPolicy(const TimeInterval &duration, const TimeInterval &max)
76  : m_duration(duration),
77  m_max(max) {
78  }
79 
80  TimeInterval BackOffTime(unsigned int failed_attempts) const {
81  TimeInterval interval = m_duration * failed_attempts;
82  if (interval > m_max)
83  interval = m_max;
84  return interval;
85  }
86 
87  private:
88  const TimeInterval m_duration;
89  const TimeInterval m_max;
90 };
91 
92 
99  public:
100  ExponentialBackoffPolicy(const TimeInterval &initial,
101  const TimeInterval &max)
102  : m_initial(initial),
103  m_max(max) {
104  }
105 
106  TimeInterval BackOffTime(unsigned int failed_attempts) const {
107  TimeInterval interval = (
108  m_initial * static_cast<int>(::pow(2, failed_attempts - 1)));
109  if (interval > m_max)
110  interval = m_max;
111  return interval;
112  }
113 
114  private:
115  const TimeInterval m_initial;
116  const TimeInterval m_max;
117 };
118 
119 
120 // TODO(simon): add an ExponentialJitterBackoffPolicy
121 
122 // Generates backoff times.
124  public:
125  explicit BackoffGenerator(const BackOffPolicy *policy)
126  : m_policy(policy),
127  m_failures(0) {
128  }
129 
130  TimeInterval Next() {
131  return m_policy->BackOffTime(++m_failures);
132  }
133 
134  void Reset() {
135  m_failures = 0;
136  }
137 
138  private:
139  std::auto_ptr<const BackOffPolicy> m_policy;
140  unsigned int m_failures;
141 };
142 } // namespace ola
143 #endif // INCLUDE_OLA_UTIL_BACKOFF_H_
A time interval, with usecond accuracy.
Definition: Clock.h:130
virtual TimeInterval BackOffTime(unsigned int failed_attempts) const =0
Calculate the backoff time.
TimeInterval BackOffTime(unsigned int) const
Calculate the backoff time.
Definition: Backoff.h:58
Definition: Backoff.h:73
Definition: Backoff.h:33
TimeInterval BackOffTime(unsigned int failed_attempts) const
Calculate the backoff time.
Definition: Backoff.h:80
Definition: Backoff.h:123
Definition: Backoff.h:98
Definition: Backoff.h:52
The namespace containing all OLA symbols.
Definition: Credentials.cpp:44
TimeInterval BackOffTime(unsigned int failed_attempts) const
Calculate the backoff time.
Definition: Backoff.h:106