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Elasticsearch subproject :client:sniffer
/*
* Licensed to Elasticsearch B.V. under one or more contributor
* license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright
* ownership. Elasticsearch B.V. 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.elasticsearch.client.sniff;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.elasticsearch.client.Node;
import org.elasticsearch.client.RestClient;
import org.elasticsearch.client.RestClientBuilder;
import java.io.Closeable;
import java.io.IOException;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Collection;
import java.util.List;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicReference;
/**
* Class responsible for sniffing nodes from some source (default is elasticsearch itself) and setting them to a provided instance of
* {@link RestClient}. Must be created via {@link SnifferBuilder}, which allows to set all of the different options or rely on defaults.
* A background task fetches the nodes through the {@link NodesSniffer} and sets them to the {@link RestClient} instance.
* It is possible to perform sniffing on failure by creating a {@link SniffOnFailureListener} and providing it as an argument to
* {@link RestClientBuilder#setFailureListener(RestClient.FailureListener)}. The Sniffer implementation needs to be lazily set to the
* previously created SniffOnFailureListener through {@link SniffOnFailureListener#setSniffer(Sniffer)}.
*/
public class Sniffer implements Closeable {
private static final Log logger = LogFactory.getLog(Sniffer.class);
private static final String SNIFFER_THREAD_NAME = "es_rest_client_sniffer";
private final NodesSniffer nodesSniffer;
private final RestClient restClient;
private final long sniffIntervalMillis;
private final long sniffAfterFailureDelayMillis;
private final Scheduler scheduler;
private final AtomicBoolean initialized = new AtomicBoolean(false);
private volatile ScheduledTask nextScheduledTask;
Sniffer(RestClient restClient, NodesSniffer nodesSniffer, long sniffInterval, long sniffAfterFailureDelay) {
this(restClient, nodesSniffer, new DefaultScheduler(), sniffInterval, sniffAfterFailureDelay);
}
Sniffer(RestClient restClient, NodesSniffer nodesSniffer, Scheduler scheduler, long sniffInterval, long sniffAfterFailureDelay) {
this.nodesSniffer = nodesSniffer;
this.restClient = restClient;
this.sniffIntervalMillis = sniffInterval;
this.sniffAfterFailureDelayMillis = sniffAfterFailureDelay;
this.scheduler = scheduler;
/*
* The first sniffing round is async, so this constructor returns before nextScheduledTask is assigned to a task.
* The initialized flag is a protection against NPE due to that.
*/
Task task = new Task(sniffIntervalMillis) {
@Override
public void run() {
super.run();
initialized.compareAndSet(false, true);
}
};
/*
* We do not keep track of the returned future as we never intend to cancel the initial sniffing round, we rather
* prevent any other operation from being executed till the sniffer is properly initialized
*/
scheduler.schedule(task, 0L);
}
/**
* Schedule sniffing to run as soon as possible if it isn't already running. Once such sniffing round runs
* it will also schedule a new round after sniffAfterFailureDelay ms.
*/
public void sniffOnFailure() {
// sniffOnFailure does nothing until the initial sniffing round has been completed
if (initialized.get()) {
/*
* If sniffing is already running, there is no point in scheduling another round right after the current one.
* Concurrent calls may be checking the same task state, but only the first skip call on the same task returns true.
* The task may also get replaced while we check its state, in which case calling skip on it returns false.
*/
if (this.nextScheduledTask.skip()) {
/*
* We do not keep track of this future as the task will immediately run and we don't intend to cancel it
* due to concurrent sniffOnFailure runs. Effectively the previous (now cancelled or skipped) task will stay
* assigned to nextTask till this onFailure round gets run and schedules its corresponding afterFailure round.
*/
scheduler.schedule(new Task(sniffAfterFailureDelayMillis), 0L);
}
}
}
enum TaskState {
WAITING,
SKIPPED,
STARTED
}
class Task implements Runnable {
final long nextTaskDelay;
final AtomicReference taskState = new AtomicReference<>(TaskState.WAITING);
Task(long nextTaskDelay) {
this.nextTaskDelay = nextTaskDelay;
}
@Override
public void run() {
/*
* Skipped or already started tasks do nothing. In most cases tasks will be cancelled and not run, but we want to protect for
* cases where future#cancel returns true yet the task runs. We want to make sure that such tasks do nothing otherwise they will
* schedule another round at the end and so on, leaving us with multiple parallel sniffing "tracks" whish is undesirable.
*/
if (taskState.compareAndSet(TaskState.WAITING, TaskState.STARTED) == false) {
return;
}
try {
sniff();
} catch (Exception e) {
logger.error("error while sniffing nodes", e);
} finally {
Task task = new Task(sniffIntervalMillis);
Future future = scheduler.schedule(task, nextTaskDelay);
// tasks are run by a single threaded executor, so swapping is safe with a simple volatile variable
ScheduledTask previousTask = nextScheduledTask;
nextScheduledTask = new ScheduledTask(task, future);
assert initialized.get() == false || previousTask.task.isSkipped() || previousTask.task.hasStarted()
: "task that we are replacing is neither cancelled nor has it ever started";
}
}
/**
* Returns true if the task has started, false in case it didn't start (yet?) or it was skipped
*/
boolean hasStarted() {
return taskState.get() == TaskState.STARTED;
}
/**
* Sets this task to be skipped. Returns true if the task will be skipped, false if the task has already started.
*/
boolean skip() {
/*
* Threads may still get run although future#cancel returns true. We make sure that a task is either cancelled (or skipped),
* or entirely run. In the odd case that future#cancel returns true and the thread still runs, the task won't do anything.
* In case future#cancel returns true but the task has already started, this state change will not succeed hence this method
* returns false and the task will normally run.
*/
return taskState.compareAndSet(TaskState.WAITING, TaskState.SKIPPED);
}
/**
* Returns true if the task was set to be skipped before it was started
*/
boolean isSkipped() {
return taskState.get() == TaskState.SKIPPED;
}
}
static final class ScheduledTask {
final Task task;
final Future future;
ScheduledTask(Task task, Future future) {
this.task = task;
this.future = future;
}
/**
* Cancels this task. Returns true if the task has been successfully cancelled, meaning it won't be executed
* or if it is its execution won't have any effect. Returns false if the task cannot be cancelled (possibly it was
* already cancelled or already completed).
*/
boolean skip() {
/*
* Future#cancel should return false whenever a task cannot be cancelled, most likely as it has already started. We don't
* trust it much though so we try to cancel hoping that it will work. At the same time we always call skip too, which means
* that if the task has already started the state change will fail. We could potentially not call skip when cancel returns
* false but we prefer to stay on the safe side.
*/
future.cancel(false);
return task.skip();
}
}
final void sniff() throws IOException {
List sniffedNodes = nodesSniffer.sniff();
if (logger.isDebugEnabled()) {
logger.debug("sniffed nodes: " + sniffedNodes);
}
if (sniffedNodes.isEmpty()) {
logger.warn("no nodes to set, nodes will be updated at the next sniffing round");
} else {
restClient.setNodes(sniffedNodes);
}
}
@Override
public void close() {
if (initialized.get()) {
nextScheduledTask.skip();
}
this.scheduler.shutdown();
}
/**
* Returns a new {@link SnifferBuilder} to help with {@link Sniffer} creation.
*
* @param restClient the client that gets its hosts set (via
* {@link RestClient#setNodes(Collection)}) once they are fetched
* @return a new instance of {@link SnifferBuilder}
*/
public static SnifferBuilder builder(RestClient restClient) {
return new SnifferBuilder(restClient);
}
/**
* The Scheduler interface allows to isolate the sniffing scheduling aspects so that we can test
* the sniffer by injecting when needed a custom scheduler that is more suited for testing.
*/
interface Scheduler {
/**
* Schedules the provided {@link Runnable} to be executed in delayMillis milliseconds
*/
Future schedule(Task task, long delayMillis);
/**
* Shuts this scheduler down
*/
void shutdown();
}
/**
* Default implementation of {@link Scheduler}, based on {@link ScheduledExecutorService}
*/
static final class DefaultScheduler implements Scheduler {
final ScheduledExecutorService executor;
DefaultScheduler() {
this(initScheduledExecutorService());
}
DefaultScheduler(ScheduledExecutorService executor) {
this.executor = executor;
}
private static ScheduledExecutorService initScheduledExecutorService() {
ScheduledThreadPoolExecutor executor = new ScheduledThreadPoolExecutor(1, new SnifferThreadFactory(SNIFFER_THREAD_NAME));
executor.setRemoveOnCancelPolicy(true);
return executor;
}
@Override
public Future schedule(Task task, long delayMillis) {
return executor.schedule(task, delayMillis, TimeUnit.MILLISECONDS);
}
@Override
public void shutdown() {
executor.shutdown();
try {
if (executor.awaitTermination(1000, TimeUnit.MILLISECONDS)) {
return;
}
executor.shutdownNow();
} catch (InterruptedException ignore) {
Thread.currentThread().interrupt();
}
}
}
static class SnifferThreadFactory implements ThreadFactory {
private final AtomicInteger threadNumber = new AtomicInteger(1);
private final String namePrefix;
private final ThreadFactory originalThreadFactory;
private SnifferThreadFactory(String namePrefix) {
this.namePrefix = namePrefix;
this.originalThreadFactory = AccessController.doPrivileged(new PrivilegedAction() {
@Override
public ThreadFactory run() {
return Executors.defaultThreadFactory();
}
});
}
@Override
public Thread newThread(final Runnable r) {
return AccessController.doPrivileged(new PrivilegedAction() {
@Override
public Thread run() {
Thread t = originalThreadFactory.newThread(r);
t.setName(namePrefix + "[T#" + threadNumber.getAndIncrement() + "]");
t.setDaemon(true);
return t;
}
});
}
}
}