/**
* 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.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/>
* <code><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></code>
*/
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
{
T result = null;
RetryLoop retryLoop = client.newRetryLoop();
while ( retryLoop.shouldContinue() )
{
try
{
client.internalBlockUntilConnectedOrTimedOut();
result = proc.call();
retryLoop.markComplete();
}
catch ( Exception e )
{
retryLoop.takeException(e);
}
}
return result;
}
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());
}
/**
* 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) )
{
tracer.get().addCount("retries-allowed", 1);
if ( !Boolean.getBoolean(DebugUtils.PROPERTY_DONT_LOG_CONNECTION_ISSUES) )
{
log.debug("Retrying operation");
}
rethrow = false;
}
else
{
tracer.get().addCount("retries-disallowed", 1);
if ( !Boolean.getBoolean(DebugUtils.PROPERTY_DONT_LOG_CONNECTION_ISSUES) )
{
log.debug("Retry policy not allowing retry");
}
}
}
if ( rethrow )
{
throw exception;
}
}
}