/*
*
* 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.solr.cloud;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.TreeMap;
import org.apache.solr.common.SolrException;
import org.apache.solr.common.SolrException.ErrorCode;
import org.apache.solr.common.cloud.SolrZkClient;
import org.apache.solr.common.cloud.ZkCmdExecutor;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooDefs;
import org.apache.zookeeper.data.ACL;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* A distributed queue from zk recipes.
*/
public class DistributedQueue {
private static final Logger LOG = LoggerFactory
.getLogger(DistributedQueue.class);
private static long DEFAULT_TIMEOUT = 5*60*1000;
private final String dir;
private SolrZkClient zookeeper;
private List<ACL> acl = ZooDefs.Ids.OPEN_ACL_UNSAFE;
private final String prefix = "qn-";
private final String response_prefix = "qnr-" ;
public DistributedQueue(SolrZkClient zookeeper, String dir, List<ACL> acl) {
this.dir = dir;
ZkCmdExecutor cmdExecutor = new ZkCmdExecutor(zookeeper.getZkClientTimeout());
try {
cmdExecutor.ensureExists(dir, zookeeper);
} catch (KeeperException e) {
throw new SolrException(ErrorCode.SERVER_ERROR, e);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
throw new SolrException(ErrorCode.SERVER_ERROR, e);
}
if (acl != null) {
this.acl = acl;
}
this.zookeeper = zookeeper;
}
/**
* Returns a Map of the children, ordered by id.
*
* @param watcher
* optional watcher on getChildren() operation.
* @return map from id to child name for all children
*/
private TreeMap<Long,String> orderedChildren(Watcher watcher)
throws KeeperException, InterruptedException {
TreeMap<Long,String> orderedChildren = new TreeMap<>();
List<String> childNames = null;
try {
childNames = zookeeper.getChildren(dir, watcher, true);
} catch (KeeperException.NoNodeException e) {
throw e;
}
for (String childName : childNames) {
try {
// Check format
if (!childName.regionMatches(0, prefix, 0, prefix.length())) {
LOG.debug("Found child node with improper name: " + childName);
continue;
}
String suffix = childName.substring(prefix.length());
Long childId = new Long(suffix);
orderedChildren.put(childId, childName);
} catch (NumberFormatException e) {
LOG.warn("Found child node with improper format : " + childName + " "
+ e, e);
}
}
return orderedChildren;
}
/**
* Return the head of the queue without modifying the queue.
*
* @return the data at the head of the queue.
*/
private QueueEvent element() throws KeeperException,
InterruptedException {
TreeMap<Long,String> orderedChildren;
// element, take, and remove follow the same pattern.
// We want to return the child node with the smallest sequence number.
// Since other clients are remove()ing and take()ing nodes concurrently,
// the child with the smallest sequence number in orderedChildren might be
// gone by the time we check.
// We don't call getChildren again until we have tried the rest of the nodes
// in sequence order.
while (true) {
try {
orderedChildren = orderedChildren(null);
} catch (KeeperException.NoNodeException e) {
return null;
}
if (orderedChildren.size() == 0) return null;
for (String headNode : orderedChildren.values()) {
if (headNode != null) {
try {
return new QueueEvent(dir + "/" + headNode, zookeeper.getData(dir + "/" + headNode, null, null, true), null);
} catch (KeeperException.NoNodeException e) {
// Another client removed the node first, try next
}
}
}
}
}
/**
* Attempts to remove the head of the queue and return it.
*
* @return The former head of the queue
*/
public byte[] remove() throws NoSuchElementException, KeeperException,
InterruptedException {
TreeMap<Long,String> orderedChildren;
// Same as for element. Should refactor this.
while (true) {
try {
orderedChildren = orderedChildren(null);
} catch (KeeperException.NoNodeException e) {
throw new NoSuchElementException();
}
if (orderedChildren.size() == 0) throw new NoSuchElementException();
for (String headNode : orderedChildren.values()) {
String path = dir + "/" + headNode;
try {
byte[] data = zookeeper.getData(path, null, null, true);
zookeeper.delete(path, -1, true);
return data;
} catch (KeeperException.NoNodeException e) {
// Another client deleted the node first.
}
}
}
}
/**
* Remove the event and save the response into the other path.
*
*/
public byte[] remove(QueueEvent event) throws KeeperException,
InterruptedException {
String path = event.getId();
String responsePath = dir + "/" + response_prefix
+ path.substring(path.lastIndexOf("-") + 1);
if (zookeeper.exists(responsePath, true)) {
zookeeper.setData(responsePath, event.getBytes(), true);
}
byte[] data = zookeeper.getData(path, null, null, true);
zookeeper.delete(path, -1, true);
return data;
}
private class LatchChildWatcher implements Watcher {
Object lock = new Object();
private WatchedEvent event = null;
public LatchChildWatcher() {}
public LatchChildWatcher(Object lock) {
this.lock = lock;
}
@Override
public void process(WatchedEvent event) {
LOG.info("LatchChildWatcher fired on path: " + event.getPath() + " state: "
+ event.getState() + " type " + event.getType());
synchronized (lock) {
this.event = event;
lock.notifyAll();
}
}
public void await(long timeout) throws InterruptedException {
synchronized (lock) {
lock.wait(timeout);
}
}
public WatchedEvent getWatchedEvent() {
return event;
}
}
/**
* Removes the head of the queue and returns it, blocks until it succeeds.
*
* @return The former head of the queue
*/
public byte[] take() throws KeeperException, InterruptedException {
TreeMap<Long,String> orderedChildren;
// Same as for element. Should refactor this.
while (true) {
LatchChildWatcher childWatcher = new LatchChildWatcher();
try {
orderedChildren = orderedChildren(childWatcher);
} catch (KeeperException.NoNodeException e) {
zookeeper.create(dir, new byte[0], acl, CreateMode.PERSISTENT, true);
continue;
}
if (orderedChildren.size() == 0) {
childWatcher.await(DEFAULT_TIMEOUT);
continue;
}
for (String headNode : orderedChildren.values()) {
String path = dir + "/" + headNode;
try {
byte[] data = zookeeper.getData(path, null, null, true);
zookeeper.delete(path, -1, true);
return data;
} catch (KeeperException.NoNodeException e) {
// Another client deleted the node first.
}
}
}
}
/**
* Inserts data into queue.
*
* @return true if data was successfully added
*/
public boolean offer(byte[] data) throws KeeperException,
InterruptedException {
return createData(dir + "/" + prefix, data,
CreateMode.PERSISTENT_SEQUENTIAL) != null;
}
/**
* Inserts data into zookeeper.
*
* @return true if data was successfully added
*/
private String createData(String path, byte[] data, CreateMode mode)
throws KeeperException, InterruptedException {
for (;;) {
try {
return zookeeper.create(path, data, acl, mode, true);
} catch (KeeperException.NoNodeException e) {
try {
zookeeper.create(dir, new byte[0], acl, CreateMode.PERSISTENT, true);
} catch (KeeperException.NodeExistsException ne) {
// someone created it
}
}
}
}
/**
* Offer the data and wait for the response
*
*/
public QueueEvent offer(byte[] data, long timeout) throws KeeperException,
InterruptedException {
String path = createData(dir + "/" + prefix, data,
CreateMode.PERSISTENT_SEQUENTIAL);
String watchID = createData(
dir + "/" + response_prefix + path.substring(path.lastIndexOf("-") + 1),
null, CreateMode.EPHEMERAL);
Object lock = new Object();
LatchChildWatcher watcher = new LatchChildWatcher(lock);
synchronized (lock) {
if (zookeeper.exists(watchID, watcher, true) != null) {
watcher.await(timeout);
}
}
byte[] bytes = zookeeper.getData(watchID, null, null, true);
zookeeper.delete(watchID, -1, true);
return new QueueEvent(watchID, bytes, watcher.getWatchedEvent());
}
/**
* Returns the data at the first element of the queue, or null if the queue is
* empty.
*
* @return data at the first element of the queue, or null.
*/
public byte[] peek() throws KeeperException, InterruptedException {
QueueEvent element = element();
if(element == null) return null;
return element.getBytes();
}
public static class QueueEvent {
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((id == null) ? 0 : id.hashCode());
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj) return true;
if (obj == null) return false;
if (getClass() != obj.getClass()) return false;
QueueEvent other = (QueueEvent) obj;
if (id == null) {
if (other.id != null) return false;
} else if (!id.equals(other.id)) return false;
return true;
}
private WatchedEvent event = null;
private String id;
private byte[] bytes;
QueueEvent(String id, byte[] bytes, WatchedEvent event) {
this.id = id;
this.bytes = bytes;
this.event = event;
}
public void setId(String id) {
this.id = id;
}
public String getId() {
return id;
}
public void setBytes(byte[] bytes) {
this.bytes = bytes;
}
public byte[] getBytes() {
return bytes;
}
public WatchedEvent getWatchedEvent() {
return event;
}
}
/**
* Returns the data at the first element of the queue, or null if the queue is
* empty and block is false.
*
* @param block if true, blocks until an element enters the queue
* @return data at the first element of the queue, or null.
*/
public QueueEvent peek(boolean block) throws KeeperException, InterruptedException {
return peek(block ? Long.MAX_VALUE : 0);
}
/**
* Returns the data at the first element of the queue, or null if the queue is
* empty after wait ms.
*
* @param wait max wait time in ms.
* @return data at the first element of the queue, or null.
*/
public QueueEvent peek(long wait) throws KeeperException, InterruptedException {
if (wait == 0) {
return element();
}
TreeMap<Long,String> orderedChildren;
boolean waitedEnough = false;
while (true) {
LatchChildWatcher childWatcher = new LatchChildWatcher();
try {
orderedChildren = orderedChildren(childWatcher);
} catch (KeeperException.NoNodeException e) {
zookeeper.create(dir, new byte[0], acl, CreateMode.PERSISTENT, true);
continue;
}
if(waitedEnough) {
if(orderedChildren.isEmpty()) return null;
}
if (orderedChildren.size() == 0) {
childWatcher.await(wait == Long.MAX_VALUE ? DEFAULT_TIMEOUT: wait);
waitedEnough = wait != Long.MAX_VALUE;
continue;
}
for (String headNode : orderedChildren.values()) {
String path = dir + "/" + headNode;
try {
byte[] data = zookeeper.getData(path, null, null, true);
return new QueueEvent(path, data, childWatcher.getWatchedEvent());
} catch (KeeperException.NoNodeException e) {
// Another client deleted the node first.
}
}
}
}
/**
* Attempts to remove the head of the queue and return it. Returns null if the
* queue is empty.
*
* @return Head of the queue or null.
*/
public byte[] poll() throws KeeperException, InterruptedException {
try {
return remove();
} catch (NoSuchElementException e) {
return null;
}
}
}