package org.apache.helix.lock.zk;
import java.util.List;
import java.util.concurrent.atomic.AtomicBoolean;
import org.apache.log4j.Logger;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.ZooDefs;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.data.ACL;
import org.apache.zookeeper.data.Stat;
/*
* 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.
*/
/**
* A base class for protocol implementations which provides a number of higher
* level helper methods for working with ZooKeeper along with retrying synchronous
* operations if the connection to ZooKeeper closes such as
* {@link #retryOperation(ZooKeeperOperation)}
*/
class ProtocolSupport {
private static final Logger LOG = Logger.getLogger(ProtocolSupport.class);
protected final ZooKeeper zookeeper;
private AtomicBoolean closed = new AtomicBoolean(false);
private long retryDelay = 500L;
private int retryCount = 10;
private List<ACL> acl = ZooDefs.Ids.OPEN_ACL_UNSAFE;
public ProtocolSupport(ZooKeeper zookeeper) {
this.zookeeper = zookeeper;
}
/**
* Closes this strategy and releases any ZooKeeper resources; but keeps the
* ZooKeeper instance open
*/
public void close() {
if (closed.compareAndSet(false, true)) {
doClose();
}
}
/**
* return zookeeper client instance
* @return zookeeper client instance
*/
public ZooKeeper getZookeeper() {
return zookeeper;
}
/**
* return the acl its using
* @return the acl.
*/
public List<ACL> getAcl() {
return acl;
}
/**
* set the acl
* @param acl the acl to set to
*/
public void setAcl(List<ACL> acl) {
this.acl = acl;
}
/**
* get the retry delay in milliseconds
* @return the retry delay
*/
public long getRetryDelay() {
return retryDelay;
}
/**
* Sets the time waited between retry delays
* @param retryDelay the retry delay
*/
public void setRetryDelay(long retryDelay) {
this.retryDelay = retryDelay;
}
/**
* Allow derived classes to perform
* some custom closing operations to release resources
*/
protected void doClose() {
}
/**
* Perform the given operation, retrying if the connection fails
* @return object. it needs to be cast to the callee's expected
* return type.
*/
protected Object retryOperation(ZooKeeperOperation operation) throws KeeperException,
InterruptedException {
KeeperException exception = null;
for (int i = 0; i < retryCount; i++) {
try {
return operation.execute();
} catch (KeeperException.SessionExpiredException e) {
LOG.warn("Session expired for: " + zookeeper + " so reconnecting due to: " + e, e);
throw e;
} catch (KeeperException.ConnectionLossException e) {
if (exception == null) {
exception = e;
}
LOG.debug("Attempt " + i + " failed with connection loss so " + "attempting to reconnect: "
+ e, e);
retryDelay(i);
}
}
throw exception;
}
/**
* Ensures that the given path exists with no data, the current
* ACL and no flags
* @param path
*/
protected void ensurePathExists(String path) {
ensureExists(path, null, acl, CreateMode.PERSISTENT);
}
/**
* Ensures that the given path exists with the given data, ACL and flags
* @param path
* @param acl
* @param flags
*/
protected void ensureExists(final String path, final byte[] data, final List<ACL> acl,
final CreateMode flags) {
try {
retryOperation(new ZooKeeperOperation() {
public boolean execute() throws KeeperException, InterruptedException {
Stat stat = zookeeper.exists(path, false);
if (stat != null) {
return true;
}
zookeeper.create(path, data, acl, flags);
return true;
}
});
} catch (KeeperException e) {
LOG.warn("Caught: " + e, e);
} catch (InterruptedException e) {
LOG.warn("Caught: " + e, e);
}
}
/**
* Returns true if this protocol has been closed
* @return true if this protocol is closed
*/
protected boolean isClosed() {
return closed.get();
}
/**
* Performs a retry delay if this is not the first attempt
* @param attemptCount the number of the attempts performed so far
*/
protected void retryDelay(int attemptCount) {
if (attemptCount > 0) {
try {
Thread.sleep(attemptCount * retryDelay);
} catch (InterruptedException e) {
LOG.debug("Failed to sleep: " + e, e);
}
}
}
}