/usr/include/ola/util/Backoff.h is in libola-dev 0.10.5.nojsmin-3.
This file is owned by root:root, with mode 0o644.
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* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*
* Backoff.h
* Copyright (C) 2013 Simon Newton
*/
#ifndef INCLUDE_OLA_UTIL_BACKOFF_H_
#define INCLUDE_OLA_UTIL_BACKOFF_H_
#include <math.h>
#include <ola/Clock.h>
#include <memory>
namespace ola {
/**
* A backoff policy will calculate how long to wait before retrying an event
* given the number of previous failed attempts.
*/
class BackOffPolicy {
public:
BackOffPolicy() {}
virtual ~BackOffPolicy() {}
/**
* @brief Calculate the backoff time
* @param failed_attempts is the number of unsuccessfull connection
* attempts since the last successful connection.
* @return how long to wait before the next attempt
*/
virtual TimeInterval BackOffTime(unsigned int failed_attempts) const = 0;
};
/**
* Constant time back off policy. For a duration of 1s we'd produce.
* 1, 1, 1, 1, 1, ...
*/
class ConstantBackoffPolicy: public BackOffPolicy {
public:
explicit ConstantBackoffPolicy(const TimeInterval &duration)
: m_duration(duration) {
}
TimeInterval BackOffTime(unsigned int) const {
return m_duration;
}
private:
const TimeInterval m_duration;
};
/**
* A backoff policy which is:
* t = failed_attempts * duration
* For a duration of 1 and a max of 5 we'd produce:
* 0, 1, 2, 3, 4, 5, 5, 5, ...
*/
class LinearBackoffPolicy: public BackOffPolicy {
public:
LinearBackoffPolicy(const TimeInterval &duration, const TimeInterval &max)
: m_duration(duration),
m_max(max) {
}
TimeInterval BackOffTime(unsigned int failed_attempts) const {
TimeInterval interval = m_duration * failed_attempts;
if (interval > m_max)
interval = m_max;
return interval;
}
private:
const TimeInterval m_duration;
const TimeInterval m_max;
};
/**
* An exponential backoff policy.
* For an initial value of 1 and a max of 20 we'd produce:
* 0, 1, 2, 4, 8, 16, 20, 20, ...
*/
class ExponentialBackoffPolicy: public BackOffPolicy {
public:
ExponentialBackoffPolicy(const TimeInterval &initial,
const TimeInterval &max)
: m_initial(initial),
m_max(max) {
}
TimeInterval BackOffTime(unsigned int failed_attempts) const {
TimeInterval interval = (
m_initial * static_cast<int>(::pow(2, failed_attempts - 1)));
if (interval > m_max)
interval = m_max;
return interval;
}
private:
const TimeInterval m_initial;
const TimeInterval m_max;
};
// TODO(simon): add an ExponentialJitterBackoffPolicy
// Generates backoff times.
class BackoffGenerator {
public:
explicit BackoffGenerator(const BackOffPolicy *policy)
: m_policy(policy),
m_failures(0) {
}
TimeInterval Next() {
return m_policy->BackOffTime(++m_failures);
}
void Reset() {
m_failures = 0;
}
private:
std::auto_ptr<const BackOffPolicy> m_policy;
unsigned int m_failures;
};
} // namespace ola
#endif // INCLUDE_OLA_UTIL_BACKOFF_H_
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