2fa7a0aa57
Motivation: We are currently always remove all entries from the cache for a hostname if the lowest TTL was reached but schedule one for each of the cached entries. This is wasteful. Modifications: - Reimplement logic to schedule TTL to only schedule a new removal task if the requested TTL was actual lower then the one for the already scheduled task. - Ensure we only remove from the internal map if we did not replace the Entries in the meantime. Result: Less overhead in terms of scheduled tasks for the DefaultDnsCache
399 lines
15 KiB
Java
399 lines
15 KiB
Java
/*
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* Copyright 2016 The Netty Project
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*
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* The Netty Project licenses this file to you under the Apache License,
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* version 2.0 (the "License"); you may not use this file except in compliance
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* with the License. You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*/
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package io.netty.resolver.dns;
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import io.netty.channel.EventLoop;
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import io.netty.handler.codec.dns.DnsRecord;
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import io.netty.util.internal.PlatformDependent;
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import io.netty.util.internal.StringUtil;
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import io.netty.util.internal.UnstableApi;
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import java.net.InetAddress;
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import java.util.ArrayList;
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import java.util.Collections;
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import java.util.Iterator;
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import java.util.List;
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import java.util.Map;
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import java.util.concurrent.ConcurrentMap;
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import java.util.concurrent.Delayed;
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import java.util.concurrent.ScheduledFuture;
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import java.util.concurrent.TimeUnit;
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import java.util.concurrent.atomic.AtomicReference;
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import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
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import static io.netty.util.internal.ObjectUtil.checkNotNull;
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import static io.netty.util.internal.ObjectUtil.checkPositiveOrZero;
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/**
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* Default implementation of {@link DnsCache}, backed by a {@link ConcurrentMap}.
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* If any additional {@link DnsRecord} is used, no caching takes place.
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*/
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@UnstableApi
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public class DefaultDnsCache implements DnsCache {
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// Two years are supported by all our EventLoop implementations and so safe to use as maximum.
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// See also: https://github.com/netty/netty/commit/b47fb817991b42ec8808c7d26538f3f2464e1fa6
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private static final int MAX_SUPPORTED_TTL_SECS = (int) TimeUnit.DAYS.toSeconds(365 * 2);
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private static final ScheduledFuture<?> CANCELLED = new ScheduledFuture<Object>() {
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@Override
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public boolean cancel(boolean mayInterruptIfRunning) {
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return false;
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}
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@Override
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public long getDelay(TimeUnit unit) {
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// We ignore unit and always return the minimum value to ensure the TTL of the cancelled marker is
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// the smallest.
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return Long.MIN_VALUE;
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}
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@Override
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public int compareTo(Delayed o) {
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throw new UnsupportedOperationException();
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}
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@Override
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public boolean isCancelled() {
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return true;
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}
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@Override
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public boolean isDone() {
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return true;
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}
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@Override
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public Object get() {
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throw new UnsupportedOperationException();
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}
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@Override
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public Object get(long timeout, TimeUnit unit) {
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throw new UnsupportedOperationException();
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}
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};
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private static final AtomicReferenceFieldUpdater<DefaultDnsCache.Entries, ScheduledFuture> FUTURE_UPDATER =
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AtomicReferenceFieldUpdater.newUpdater(
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DefaultDnsCache.Entries.class, ScheduledFuture.class, "expirationFuture");
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private final ConcurrentMap<String, Entries> resolveCache = PlatformDependent.newConcurrentHashMap();
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private final int minTtl;
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private final int maxTtl;
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private final int negativeTtl;
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/**
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* Create a cache that respects the TTL returned by the DNS server
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* and doesn't cache negative responses.
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*/
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public DefaultDnsCache() {
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this(0, MAX_SUPPORTED_TTL_SECS, 0);
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}
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/**
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* Create a cache.
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* @param minTtl the minimum TTL
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* @param maxTtl the maximum TTL
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* @param negativeTtl the TTL for failed queries
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*/
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public DefaultDnsCache(int minTtl, int maxTtl, int negativeTtl) {
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this.minTtl = Math.min(MAX_SUPPORTED_TTL_SECS, checkPositiveOrZero(minTtl, "minTtl"));
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this.maxTtl = Math.min(MAX_SUPPORTED_TTL_SECS, checkPositiveOrZero(maxTtl, "maxTtl"));
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if (minTtl > maxTtl) {
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throw new IllegalArgumentException(
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"minTtl: " + minTtl + ", maxTtl: " + maxTtl + " (expected: 0 <= minTtl <= maxTtl)");
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}
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this.negativeTtl = checkPositiveOrZero(negativeTtl, "negativeTtl");
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}
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/**
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* Returns the minimum TTL of the cached DNS resource records (in seconds).
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*
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* @see #maxTtl()
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*/
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public int minTtl() {
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return minTtl;
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}
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/**
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* Returns the maximum TTL of the cached DNS resource records (in seconds).
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*
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* @see #minTtl()
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*/
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public int maxTtl() {
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return maxTtl;
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}
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/**
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* Returns the TTL of the cache for the failed DNS queries (in seconds). The default value is {@code 0}, which
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* disables the cache for negative results.
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*/
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public int negativeTtl() {
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return negativeTtl;
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}
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@Override
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public void clear() {
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while (!resolveCache.isEmpty()) {
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for (Iterator<Map.Entry<String, Entries>> i = resolveCache.entrySet().iterator(); i.hasNext();) {
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Map.Entry<String, Entries> e = i.next();
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i.remove();
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e.getValue().clearAndCancel();
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}
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}
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}
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@Override
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public boolean clear(String hostname) {
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checkNotNull(hostname, "hostname");
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Entries entries = resolveCache.remove(appendDot(hostname));
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return entries != null && entries.clearAndCancel();
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}
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private static boolean emptyAdditionals(DnsRecord[] additionals) {
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return additionals == null || additionals.length == 0;
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}
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@Override
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public List<? extends DnsCacheEntry> get(String hostname, DnsRecord[] additionals) {
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checkNotNull(hostname, "hostname");
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if (!emptyAdditionals(additionals)) {
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return Collections.<DnsCacheEntry>emptyList();
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}
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Entries entries = resolveCache.get(appendDot(hostname));
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return entries == null ? null : entries.get();
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}
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@Override
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public DnsCacheEntry cache(String hostname, DnsRecord[] additionals,
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InetAddress address, long originalTtl, EventLoop loop) {
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checkNotNull(hostname, "hostname");
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checkNotNull(address, "address");
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checkNotNull(loop, "loop");
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final DefaultDnsCacheEntry e = new DefaultDnsCacheEntry(hostname, address);
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if (maxTtl == 0 || !emptyAdditionals(additionals)) {
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return e;
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}
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cache0(appendDot(hostname), e,
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Math.max(minTtl, (int) Math.min(maxTtl, originalTtl)), loop);
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return e;
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}
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@Override
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public DnsCacheEntry cache(String hostname, DnsRecord[] additionals, Throwable cause, EventLoop loop) {
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checkNotNull(hostname, "hostname");
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checkNotNull(cause, "cause");
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checkNotNull(loop, "loop");
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final DefaultDnsCacheEntry e = new DefaultDnsCacheEntry(hostname, cause);
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if (negativeTtl == 0 || !emptyAdditionals(additionals)) {
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return e;
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}
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cache0(appendDot(hostname), e, negativeTtl, loop);
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return e;
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}
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private void cache0(String hostname, DefaultDnsCacheEntry e, int ttl, EventLoop loop) {
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Entries entries = resolveCache.get(hostname);
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if (entries == null) {
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entries = new Entries(hostname);
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Entries oldEntries = resolveCache.putIfAbsent(hostname, entries);
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if (oldEntries != null) {
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entries = oldEntries;
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}
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}
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entries.add(e, ttl, loop);
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}
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@Override
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public String toString() {
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return new StringBuilder()
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.append("DefaultDnsCache(minTtl=")
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.append(minTtl).append(", maxTtl=")
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.append(maxTtl).append(", negativeTtl=")
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.append(negativeTtl).append(", cached resolved hostname=")
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.append(resolveCache.size()).append(")")
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.toString();
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}
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private static final class DefaultDnsCacheEntry implements DnsCacheEntry {
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private final String hostname;
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private final InetAddress address;
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private final Throwable cause;
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DefaultDnsCacheEntry(String hostname, InetAddress address) {
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this.hostname = checkNotNull(hostname, "hostname");
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this.address = checkNotNull(address, "address");
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cause = null;
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}
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DefaultDnsCacheEntry(String hostname, Throwable cause) {
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this.hostname = checkNotNull(hostname, "hostname");
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this.cause = checkNotNull(cause, "cause");
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address = null;
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}
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@Override
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public InetAddress address() {
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return address;
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}
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@Override
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public Throwable cause() {
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return cause;
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}
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String hostname() {
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return hostname;
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}
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@Override
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public String toString() {
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if (cause != null) {
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return hostname + '/' + cause;
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} else {
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return address.toString();
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}
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}
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}
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// Directly extend AtomicReference for intrinsics and also to keep memory overhead low.
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private final class Entries extends AtomicReference<List<DefaultDnsCacheEntry>> implements Runnable {
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private final String hostname;
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// Needs to be package-private to be able to access it via the AtomicReferenceFieldUpdater
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volatile ScheduledFuture<?> expirationFuture;
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Entries(String hostname) {
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super(Collections.<DefaultDnsCacheEntry>emptyList());
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this.hostname = hostname;
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}
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void add(DefaultDnsCacheEntry e, int ttl, EventLoop loop) {
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if (e.cause() == null) {
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for (;;) {
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List<DefaultDnsCacheEntry> entries = get();
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if (!entries.isEmpty()) {
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final DefaultDnsCacheEntry firstEntry = entries.get(0);
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if (firstEntry.cause() != null) {
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assert entries.size() == 1;
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if (compareAndSet(entries, Collections.singletonList(e))) {
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scheduleCacheExpirationIfNeeded(ttl, loop);
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return;
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} else {
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// Need to try again as CAS failed
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continue;
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}
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}
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// Create a new List for COW semantics
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List<DefaultDnsCacheEntry> newEntries = new ArrayList<DefaultDnsCacheEntry>(entries.size() + 1);
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int i = 0;
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do {
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DefaultDnsCacheEntry entry = entries.get(i);
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// Only add old entry if the address is not the same as the one we try to add as well.
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// In this case we will skip it and just add the new entry as this may have
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// more up-to-date data and cancel the old after we were able to update the cache.
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if (!e.address().equals(entry.address())) {
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newEntries.add(entry);
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}
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} while (++i < entries.size());
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newEntries.add(e);
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if (compareAndSet(entries, Collections.unmodifiableList(newEntries))) {
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scheduleCacheExpirationIfNeeded(ttl, loop);
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return;
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}
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} else if (compareAndSet(entries, Collections.singletonList(e))) {
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scheduleCacheExpirationIfNeeded(ttl, loop);
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return;
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}
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}
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} else {
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set(Collections.singletonList(e));
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scheduleCacheExpirationIfNeeded(ttl, loop);
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}
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}
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private void scheduleCacheExpirationIfNeeded(int ttl, EventLoop loop) {
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for (;;) {
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// We currently don't calculate a new TTL when we need to retry the CAS as we don't expect this to
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// be invoked very concurrently and also we use SECONDS anyway. If this ever becomes a problem
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// we can reconsider.
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ScheduledFuture<?> oldFuture = FUTURE_UPDATER.get(this);
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if (oldFuture == null || oldFuture.getDelay(TimeUnit.SECONDS) > ttl) {
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ScheduledFuture<?> newFuture = loop.schedule(this, ttl, TimeUnit.SECONDS);
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// It is possible that
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// 1. task will fire in between this line, or
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// 2. multiple timers may be set if there is concurrency
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// (1) Shouldn't be a problem because we will fail the CAS and then the next loop will see CANCELLED
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// so the ttl will not be less, and we will bail out of the loop.
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// (2) This is a trade-off to avoid concurrency resulting in contention on a synchronized block.
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if (FUTURE_UPDATER.compareAndSet(this, oldFuture, newFuture)) {
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if (oldFuture != null) {
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oldFuture.cancel(true);
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}
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break;
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} else {
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// There was something else scheduled in the meantime... Cancel and try again.
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newFuture.cancel(true);
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}
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} else {
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break;
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}
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}
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}
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boolean clearAndCancel() {
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List<DefaultDnsCacheEntry> entries = getAndSet(Collections.<DefaultDnsCacheEntry>emptyList());
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if (entries.isEmpty()) {
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return false;
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}
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ScheduledFuture<?> expirationFuture = FUTURE_UPDATER.getAndSet(this, CANCELLED);
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if (expirationFuture != null) {
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expirationFuture.cancel(false);
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}
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return true;
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}
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@Override
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public void run() {
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// We always remove all entries for a hostname once one entry expire. This is not the
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// most efficient to do but this way we can guarantee that if a DnsResolver
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// be configured to prefer one ip family over the other we will not return unexpected
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// results to the enduser if one of the A or AAAA records has different TTL settings.
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//
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// As a TTL is just a hint of the maximum time a cache is allowed to cache stuff it's
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// completely fine to remove the entry even if the TTL is not reached yet.
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//
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// See https://github.com/netty/netty/issues/7329
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resolveCache.remove(hostname, this);
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clearAndCancel();
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}
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}
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private static String appendDot(String hostname) {
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return StringUtil.endsWith(hostname, '.') ? hostname : hostname + '.';
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}
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}
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