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Backoff utilities: controller, algorithm interface and standard imple…
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…mentation

This utility provides a wrapper class for running a task with back-off retry.

The controller encapsulates the CALL->WAIT/QUIT logic; it takes a Callable which returns a simple SUCCESS/FAILURE value, and an algorithm which computes the next wait time and whether the controller loop should quit.  

The Standard implementation is that of exponential back-off (based on radix 2).  Algorithms are provided via an implementation-specific factory interface.

The utility is internal and requires no user documentation.  Its use in new features should figure as part of the settable properties for that feature.

Target: trunk
Patch: http://rb.dcache.org/r/4977
Acked-by: Paul, Dmitry
Requires-notes: no
Requires-book: no
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alrossi committed Dec 21, 2012
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136 changes: 136 additions & 0 deletions modules/common/src/main/java/org/dcache/util/backoff/BackoffControllerBuilder.java
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/*
COPYRIGHT STATUS:
Dec 1st 2001, Fermi National Accelerator Laboratory (FNAL) documents and
software are sponsored by the U.S. Department of Energy under Contract No.
DE-AC02-76CH03000. Therefore, the U.S. Government retains a world-wide
non-exclusive, royalty-free license to publish or reproduce these documents
and software for U.S. Government purposes. All documents and software
available from this server are protected under the U.S. and Foreign
Copyright Laws, and FNAL reserves all rights.
Distribution of the software available from this server is free of
charge subject to the user following the terms of the Fermitools
Software Legal Information.
Redistribution and/or modification of the software shall be accompanied
by the Fermitools Software Legal Information (including the copyright
notice).
The user is asked to feed back problems, benefits, and/or suggestions
about the software to the Fermilab Software Providers.
Neither the name of Fermilab, the URA, nor the names of the contributors
may be used to endorse or promote products derived from this software
without specific prior written permission.
DISCLAIMER OF LIABILITY (BSD):
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL FERMILAB,
OR THE URA, OR THE U.S. DEPARTMENT of ENERGY, OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
Liabilities of the Government:
This software is provided by URA, independent from its Prime Contract
with the U.S. Department of Energy. URA is acting independently from
the Government and in its own private capacity and is not acting on
behalf of the U.S. Government, nor as its contractor nor its agent.
Correspondingly, it is understood and agreed that the U.S. Government
has no connection to this software and in no manner whatsoever shall
be liable for nor assume any responsibility or obligation for any claim,
cost, or damages arising out of or resulting from the use of the software
available from this server.
Export Control:
All documents and software available from this server are subject to U.S.
export control laws. Anyone downloading information from this server is
obligated to secure any necessary Government licenses before exporting
documents or software obtained from this server.
*/
package org.dcache.util.backoff;

import static com.google.common.base.Preconditions.checkNotNull;

import java.util.concurrent.Callable;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
* Fluid builder for constructing {@link BackoffController}.
*
* @author arossi
*/
public class BackoffControllerBuilder {
/**
* Executes a {@link Callable} object in a loop controlled by an
* {@link IBackoffAlgorithm} implementation which provides the logic for
* determining how long of a wait should be executed between passes, or
* whether the thread should quit, when the call status is FAILURE.
*/
public class BackoffController {

private final Logger logger = LoggerFactory.getLogger(this.getClass());
private IBackoffAlgorithmFactory algorithmFactory;

/**
* only available to the builder
*/
private BackoffController() {
}

public IBackoffAlgorithm.Status call(Callable<IBackoffAlgorithm.Status> callable)
throws Exception {
IBackoffAlgorithm backoffAlgorithm = algorithmFactory.getAlgorithm();
IBackoffAlgorithm.Status rval = IBackoffAlgorithm.Status.FAILURE;
long wait = IBackoffAlgorithm.NO_WAIT;

while (true) {
rval = callable.call();

if (rval == IBackoffAlgorithm.Status.SUCCESS) {
break;
}

wait = backoffAlgorithm.getWaitDuration();

if (wait == IBackoffAlgorithm.NO_WAIT) {
logger.debug("algorithm returned NO_WAIT");
break;
}

synchronized (this) {
try {
wait(wait);
} catch (final InterruptedException e) {
logger.trace("wait was interrupted", e);
}
}
}

return rval;
}
}

private final BackoffController controller = new BackoffController();

public BackoffController build() {
return controller;
}

public BackoffControllerBuilder using(IBackoffAlgorithmFactory algorithmFactory) {
checkNotNull(algorithmFactory);
controller.algorithmFactory = algorithmFactory;
return this;
}
}
194 changes: 194 additions & 0 deletions modules/common/src/main/java/org/dcache/util/backoff/ExponentialBackoffAlgorithmFactory.java
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/*
COPYRIGHT STATUS:
Dec 1st 2001, Fermi National Accelerator Laboratory (FNAL) documents and
software are sponsored by the U.S. Department of Energy under Contract No.
DE-AC02-76CH03000. Therefore, the U.S. Government retains a world-wide
non-exclusive, royalty-free license to publish or reproduce these documents
and software for U.S. Government purposes. All documents and software
available from this server are protected under the U.S. and Foreign
Copyright Laws, and FNAL reserves all rights.
Distribution of the software available from this server is free of
charge subject to the user following the terms of the Fermitools
Software Legal Information.
Redistribution and/or modification of the software shall be accompanied
by the Fermitools Software Legal Information (including the copyright
notice).
The user is asked to feed back problems, benefits, and/or suggestions
about the software to the Fermilab Software Providers.
Neither the name of Fermilab, the URA, nor the names of the contributors
may be used to endorse or promote products derived from this software
without specific prior written permission.
DISCLAIMER OF LIABILITY (BSD):
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL FERMILAB,
OR THE URA, OR THE U.S. DEPARTMENT of ENERGY, OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
Liabilities of the Government:
This software is provided by URA, independent from its Prime Contract
with the U.S. Department of Energy. URA is acting independently from
the Government and in its own private capacity and is not acting on
behalf of the U.S. Government, nor as its contractor nor its agent.
Correspondingly, it is understood and agreed that the U.S. Government
has no connection to this software and in no manner whatsoever shall
be liable for nor assume any responsibility or obligation for any claim,
cost, or damages arising out of or resulting from the use of the software
available from this server.
Export Control:
All documents and software available from this server are subject to U.S.
export control laws. Anyone downloading information from this server is
obligated to secure any necessary Government licenses before exporting
documents or software obtained from this server.
*/
package org.dcache.util.backoff;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

import java.util.concurrent.TimeUnit;

/**
* Factory implementation for creating an {@link ExponentialBackoffAlgorithm}.
*
* @author arossi
*/
public class ExponentialBackoffAlgorithmFactory implements
IBackoffAlgorithmFactory {
/**
* Standard exponential backoff algorithm. Computes recursive function: <br>
* <br>
*
* W(0) = W[min] <br>
* W(n) = (W[min] + W(n-1) * 2)/2 <br>
* <br>
*
* where W[min] is the minimum delay time, and n is the attempt number. The
* algorithm can also be given a maximum delay (default is Long.MAX_VALUE).
* The minimum delay must be positive; the default is 1.
*
* <p>
* The default {@link TimeUnit} for both min and max is MINUTES.
*
* <p>
* {@link #quitAtMaxDelay} is false by default.
*
* <p>
* Note that the algorithm is stateful and therefore not thread-safe; hence
* the factory creates a new copy at each call to
* {@link ExponentialBackoffAlgorithmFactory#getAlgorithm()}.
*/
private class ExponentialBackoffAlgorithm implements IBackoffAlgorithm {

/**
* Derived
*/
private Long maxDelayInMillis;
private Long minDelayInMillis;

/**
* State
*/
private long previousDelay = 0L;
private int previousAttempts = 0;

@Override
public long getWaitDuration() {
if (previousDelay == NO_WAIT) {
return previousDelay;
}

if (previousDelay == 0) {
previousDelay = minDelayInMillis;
} else {
previousDelay = (minDelayInMillis + 2 * previousDelay) / 2;
}

if (maxDelayInMillis != null) {
/*
* catch potential overflow (negative value)
*/
if (previousDelay > maxDelayInMillis || previousDelay <= 0) {
previousDelay = maxDelayInMillis;
}

if (quitAtMaxDelay && previousDelay == maxDelayInMillis) {
previousDelay = NO_WAIT;
}
}

if (maxAllowedAttempts != null
&& ++previousAttempts >= maxAllowedAttempts) {
previousDelay = NO_WAIT;
}

return previousDelay;
}
}

/**
* Injected
*/
private Long maxDelay;
private Long minDelay = 1L;
private TimeUnit maxUnit = TimeUnit.MINUTES;
private TimeUnit minUnit = TimeUnit.MINUTES;
private Integer maxAllowedAttempts;
private boolean quitAtMaxDelay = false;

@Override
public IBackoffAlgorithm getAlgorithm() throws IllegalArgumentException {
ExponentialBackoffAlgorithm algorithm = new ExponentialBackoffAlgorithm();
algorithm.minDelayInMillis = minUnit.toMillis(minDelay);
if (maxDelay != null) {
checkArgument(maxDelay >= minDelay);
algorithm.maxDelayInMillis = maxUnit.toMillis(maxDelay);
}

return algorithm;
}

public void setMaxAllowedAttempts(Integer maxAllowedAttempts) {
this.maxAllowedAttempts = maxAllowedAttempts;
}

public void setMaxDelay(Long maxDelay) {
this.maxDelay = maxDelay;
}

public void setMaxUnit(TimeUnit maxUnit) {
checkNotNull(maxUnit);
this.maxUnit = maxUnit;
}

public void setMinDelay(Long minDelay) {
checkNotNull(minDelay);
checkArgument(minDelay > 0);
this.minDelay = minDelay;
}

public void setMinUnit(TimeUnit minUnit) {
checkNotNull(minUnit);
this.minUnit = minUnit;
}

public void setQuitAtMaxDelay(boolean quitAtMaxDelay) {
this.quitAtMaxDelay = quitAtMaxDelay;
}
}
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