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include
ola
util
Backoff.h
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/*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*
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* Backoff.h
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* Copyright (C) 2013 Simon Newton
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*/
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#ifndef INCLUDE_OLA_UTIL_BACKOFF_H_
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#define INCLUDE_OLA_UTIL_BACKOFF_H_
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#include <math.h>
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#include <ola/Clock.h>
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#include <memory>
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namespace
ola {
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class
BackOffPolicy
{
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public
:
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BackOffPolicy
() {}
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virtual
~
BackOffPolicy
() {}
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virtual
TimeInterval
BackOffTime
(
unsigned
int
failed_attempts)
const
= 0;
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};
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class
ConstantBackoffPolicy
:
public
BackOffPolicy
{
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public
:
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explicit
ConstantBackoffPolicy
(
const
TimeInterval
&duration)
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: m_duration(duration) {
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}
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TimeInterval
BackOffTime
(
unsigned
int
)
const
{
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return
m_duration;
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}
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private
:
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const
TimeInterval
m_duration;
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};
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class
LinearBackoffPolicy
:
public
BackOffPolicy
{
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public
:
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LinearBackoffPolicy
(
const
TimeInterval
&duration,
const
TimeInterval
&max)
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: m_duration(duration),
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m_max(max) {
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}
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TimeInterval
BackOffTime
(
unsigned
int
failed_attempts)
const
{
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TimeInterval
interval = m_duration * failed_attempts;
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if
(interval > m_max)
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interval = m_max;
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return
interval;
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}
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private
:
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const
TimeInterval
m_duration;
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const
TimeInterval
m_max;
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};
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class
ExponentialBackoffPolicy
:
public
BackOffPolicy
{
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public
:
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ExponentialBackoffPolicy
(
const
TimeInterval
&initial,
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const
TimeInterval
&max)
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: m_initial(initial),
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m_max(max) {
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}
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TimeInterval
BackOffTime
(
unsigned
int
failed_attempts)
const
{
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TimeInterval
interval = (
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m_initial *
static_cast<
int
>
(::pow(2, failed_attempts - 1)));
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if
(interval > m_max)
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interval = m_max;
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return
interval;
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}
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private
:
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const
TimeInterval
m_initial;
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const
TimeInterval
m_max;
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};
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// TODO(simon): add an ExponentialJitterBackoffPolicy
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// Generates backoff times.
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class
BackoffGenerator
{
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public
:
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explicit
BackoffGenerator
(
const
BackOffPolicy
*policy)
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: m_policy(policy),
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m_failures(0) {
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}
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TimeInterval
Next() {
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return
m_policy->BackOffTime(++m_failures);
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}
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void
Reset() {
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m_failures = 0;
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}
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private
:
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std::auto_ptr<const BackOffPolicy> m_policy;
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unsigned
int
m_failures;
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};
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}
// namespace ola
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#endif // INCLUDE_OLA_UTIL_BACKOFF_H_
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