Use allocation free algorithm to detect CNAME cache loops (#10291)

Motivation:

We did use a HashSet to detect CNAME cache loops which needs allocations. We can use an algorithm that doesnt need any allocations

Modifications:

Use algorithm that doesnt need allocations

Result:

Less allocations on the slow path
This commit is contained in:
Norman Maurer 2020-05-18 14:28:30 +02:00
parent 1fe92e3077
commit bdb5e20d99
2 changed files with 62 additions and 12 deletions

View File

@ -47,7 +47,6 @@ import java.util.AbstractList;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.IdentityHashMap;
import java.util.Iterator;
import java.util.List;
@ -267,8 +266,9 @@ abstract class DnsResolveContext<T> {
// Resolve the final name from the CNAME cache until there is nothing to follow anymore. This also
// guards against loops in the cache but early return once a loop is detected.
private String cnameResolveFromCache(String name) {
DnsCnameCache cnameCache = cnameCache();
//
// Visible for testing only
static String cnameResolveFromCache(DnsCnameCache cnameCache, String name) {
String first = cnameCache.get(hostnameWithDot(name));
if (first == null) {
// Nothing in the cache at all
@ -289,28 +289,30 @@ abstract class DnsResolveContext<T> {
return cnameResolveFromCacheLoop(cnameCache, first, second);
}
private String cnameResolveFromCacheLoop(DnsCnameCache cnameCache, String first, String mapping) {
// Detect loops using a HashSet. We use this as last resort implementation to reduce allocations in the most
// common cases.
Set<String> cnames = new HashSet<>(4);
cnames.add(first);
cnames.add(mapping);
static String cnameResolveFromCacheLoop(DnsCnameCache cnameCache, String first, String mapping) {
// Detect loops by advance only every other iteration.
// See https://en.wikipedia.org/wiki/Cycle_detection#Floyd's_Tortoise_and_Hare
boolean advance = false;
String name = mapping;
// Resolve from cnameCache() until there is no more cname entry cached.
while ((mapping = cnameCache.get(hostnameWithDot(name))) != null) {
if (!cnames.add(mapping)) {
if (first.equals(mapping)) {
// Follow CNAME from cache would loop. Lets break here.
break;
}
name = mapping;
if (advance) {
first = cnameCache.get(first);
}
advance = !advance;
}
return name;
}
private void internalResolve(String name, Promise<List<T>> promise) {
// Resolve from cnameCache() until there is no more cname entry cached.
name = cnameResolveFromCache(name);
name = cnameResolveFromCache(cnameCache(), name);
try {
DnsServerAddressStream nameServerAddressStream = getNameServers(name);
@ -975,7 +977,7 @@ abstract class DnsResolveContext<T> {
private void followCname(DnsQuestion question, String cname, DnsQueryLifecycleObserver queryLifecycleObserver,
Promise<List<T>> promise) {
cname = cnameResolveFromCache(cname);
cname = cnameResolveFromCache(cnameCache(), cname);
DnsServerAddressStream stream = getNameServers(cname);
final DnsQuestion cnameQuestion;

View File

@ -0,0 +1,48 @@
/*
* Copyright 2020 The Netty Project
*
* The Netty Project 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 io.netty.resolver.dns;
import io.netty.channel.embedded.EmbeddedChannel;
import org.junit.Test;
public class DnsResolveContextTest {
private static final String HOSTNAME = "netty.io.";
@Test
public void testCnameLoop() {
for (int i = 1; i < 128; i++) {
DnsResolveContext.cnameResolveFromCache(buildCache(i), HOSTNAME);
}
}
private static DnsCnameCache buildCache(int chainLength) {
EmbeddedChannel channel = new EmbeddedChannel();
DnsCnameCache cache = new DefaultDnsCnameCache();
if (chainLength == 1) {
cache.cache(HOSTNAME, HOSTNAME, Long.MAX_VALUE, channel.eventLoop());
} else {
String lastName = HOSTNAME;
for (int i = 1; i < chainLength; i++) {
String nextName = i + "." + lastName;
cache.cache(lastName, nextName, Long.MAX_VALUE, channel.eventLoop());
lastName = nextName;
}
cache.cache(lastName, HOSTNAME, Long.MAX_VALUE, channel.eventLoop());
}
return cache;
}
}