/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package org.apache.curator;
import org.apache.curator.drivers.
EventTrace;
import org.apache.curator.drivers.
TracerDriver;
import org.apache.curator.utils.
DebugUtils;
import org.apache.zookeeper.
KeeperException;
import org.slf4j.
Logger;
import org.slf4j.
LoggerFactory;
import java.util.concurrent.
Callable;
import java.util.concurrent.
TimeUnit;
import java.util.concurrent.atomic.
AtomicReference;
/**
* <p>Mechanism to perform an operation on Zookeeper that is safe against
* disconnections and "recoverable" errors.</p>
*
* <p>
* If an exception occurs during the operation, the RetryLoop will process it,
* check with the current retry policy and either attempt to reconnect or re-throw
* the exception
* </p>
*
* Canonical usage:<br>
* <pre>
* RetryLoop retryLoop = client.newRetryLoop();
* while ( retryLoop.shouldContinue() )
* {
* try
* {
* // do your work
* ZooKeeper zk = client.getZooKeeper(); // it's important to re-get the ZK instance in case there was an error and the instance was re-created
*
* retryLoop.markComplete();
* }
* catch ( Exception e )
* {
* retryLoop.takeException(e);
* }
* }
* </pre>
*/
public class
RetryLoop
{
private boolean
isDone = false;
private int
retryCount = 0;
private final
Logger log =
LoggerFactory.
getLogger(
getClass());
private final long
startTimeMs =
System.
currentTimeMillis();
private final
RetryPolicy retryPolicy;
private final
AtomicReference<
TracerDriver>
tracer;
private static final
RetrySleeper sleeper = new
RetrySleeper()
{
@
Override
public void
sleepFor(long
time,
TimeUnit unit) throws
InterruptedException
{
unit.
sleep(
time);
}
};
/**
* Returns the default retry sleeper
*
* @return sleeper
*/
public static
RetrySleeper getDefaultRetrySleeper()
{
return
sleeper;
}
/**
* Convenience utility: creates a retry loop calling the given proc and retrying if needed
*
* @param client Zookeeper
* @param proc procedure to call with retry
* @param <T> return type
* @return procedure result
* @throws Exception any non-retriable errors
*/
public static<T> T
callWithRetry(
CuratorZookeeperClient client,
Callable<T>
proc) throws
Exception
{
return
client.
getConnectionHandlingPolicy().
callWithRetry(
client,
proc);
}
RetryLoop(
RetryPolicy retryPolicy,
AtomicReference<
TracerDriver>
tracer)
{
this.
retryPolicy =
retryPolicy;
this.
tracer =
tracer;
}
/**
* If true is returned, make an attempt at the operation
*
* @return true/false
*/
public boolean
shouldContinue()
{
return !
isDone;
}
/**
* Call this when your operation has successfully completed
*/
public void
markComplete()
{
isDone = true;
}
/**
* Utility - return true if the given Zookeeper result code is retry-able
*
* @param rc result code
* @return true/false
*/
public static boolean
shouldRetry(int
rc)
{
return (
rc ==
KeeperException.
Code.
CONNECTIONLOSS.
intValue()) ||
(
rc ==
KeeperException.
Code.
OPERATIONTIMEOUT.
intValue()) ||
(
rc ==
KeeperException.
Code.
SESSIONMOVED.
intValue()) ||
(
rc ==
KeeperException.
Code.
SESSIONEXPIRED.
intValue()) ||
(
rc == -13); // KeeperException.Code.NEWCONFIGNOQUORUM.intValue()) - using hard coded value for ZK 3.4.x compatibility
}
/**
* Utility - return true if the given exception is retry-able
*
* @param exception exception to check
* @return true/false
*/
public static boolean
isRetryException(
Throwable exception)
{
if (
exception instanceof
KeeperException )
{
KeeperException keeperException = (
KeeperException)
exception;
return
shouldRetry(
keeperException.
code().
intValue());
}
return false;
}
/**
* Pass any caught exceptions here
*
* @param exception the exception
* @throws Exception if not retry-able or the retry policy returned negative
*/
public void
takeException(
Exception exception) throws
Exception
{
boolean
rethrow = true;
if (
isRetryException(
exception) )
{
if ( !
Boolean.
getBoolean(
DebugUtils.
PROPERTY_DONT_LOG_CONNECTION_ISSUES) )
{
log.
debug("Retry-able exception received",
exception);
}
if (
retryPolicy.
allowRetry(
retryCount++,
System.
currentTimeMillis() -
startTimeMs,
sleeper) )
{
new
EventTrace("retries-allowed",
tracer.
get()).
commit();
if ( !
Boolean.
getBoolean(
DebugUtils.
PROPERTY_DONT_LOG_CONNECTION_ISSUES) )
{
log.
debug("Retrying operation");
}
rethrow = false;
}
else
{
new
EventTrace("retries-disallowed",
tracer.
get()).
commit();
if ( !
Boolean.
getBoolean(
DebugUtils.
PROPERTY_DONT_LOG_CONNECTION_ISSUES) )
{
log.
debug("Retry policy not allowing retry");
}
}
}
if (
rethrow )
{
throw
exception;
}
}
}