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org.asynchttpclient.shaded.io.netty.resolver.dns.Cache Maven / Gradle / Ivy
/*
* Copyright 2018 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:
*
* https://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.asynchttpclient.shaded.io.netty.resolver.dns;
import org.asynchttpclient.shaded.io.netty.channel.EventLoop;
import org.asynchttpclient.shaded.io.netty.util.internal.PlatformDependent;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.Delayed;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
import static java.util.Collections.singletonList;
/**
* Abstract cache that automatically removes entries for a hostname once the TTL for an entry is reached.
*
* @param
*/
abstract class Cache {
private static final AtomicReferenceFieldUpdater FUTURE_UPDATER =
AtomicReferenceFieldUpdater.newUpdater(Cache.Entries.class, ScheduledFuture.class, "expirationFuture");
private static final ScheduledFuture CANCELLED = new ScheduledFuture() {
@Override
public boolean cancel(boolean mayInterruptIfRunning) {
return false;
}
@Override
public long getDelay(TimeUnit unit) {
// We ignore unit and always return the minimum value to ensure the TTL of the cancelled marker is
// the smallest.
return Long.MIN_VALUE;
}
@Override
public int compareTo(Delayed o) {
throw new UnsupportedOperationException();
}
@Override
public boolean isCancelled() {
return true;
}
@Override
public boolean isDone() {
return true;
}
@Override
public Object get() {
throw new UnsupportedOperationException();
}
@Override
public Object get(long timeout, TimeUnit unit) {
throw new UnsupportedOperationException();
}
};
// Two years are supported by all our EventLoop implementations and so safe to use as maximum.
// See also: https://github.com/netty/netty/commit/b47fb817991b42ec8808c7d26538f3f2464e1fa6
static final int MAX_SUPPORTED_TTL_SECS = (int) TimeUnit.DAYS.toSeconds(365 * 2);
private final ConcurrentMap resolveCache = PlatformDependent.newConcurrentHashMap();
/**
* Remove everything from the cache.
*/
final void clear() {
while (!resolveCache.isEmpty()) {
for (Iterator> i = resolveCache.entrySet().iterator(); i.hasNext();) {
Map.Entry e = i.next();
i.remove();
e.getValue().clearAndCancel();
}
}
}
/**
* Clear all entries (if anything exists) for the given hostname and return {@code true} if anything was removed.
*/
final boolean clear(String hostname) {
Entries entries = resolveCache.remove(hostname);
return entries != null && entries.clearAndCancel();
}
/**
* Returns all caches entries for the given hostname.
*/
final List get(String hostname) {
Entries entries = resolveCache.get(hostname);
return entries == null ? null : entries.get();
}
/**
* Cache a value for the given hostname that will automatically expire once the TTL is reached.
*/
final void cache(String hostname, E value, int ttl, EventLoop loop) {
Entries entries = resolveCache.get(hostname);
if (entries == null) {
entries = new Entries(hostname);
Entries oldEntries = resolveCache.putIfAbsent(hostname, entries);
if (oldEntries != null) {
entries = oldEntries;
}
}
entries.add(value, ttl, loop);
}
/**
* Return the number of hostames for which we have cached something.
*/
final int size() {
return resolveCache.size();
}
/**
* Returns {@code true} if this entry should replace all other entries that are already cached for the hostname.
*/
protected abstract boolean shouldReplaceAll(E entry);
/**
* Sort the {@link List} for a {@code hostname} before caching these.
*/
protected void sortEntries(
@SuppressWarnings("unused") String hostname, @SuppressWarnings("unused") List entries) {
// NOOP.
}
/**
* Returns {@code true} if both entries are equal.
*/
protected abstract boolean equals(E entry, E otherEntry);
// Directly extend AtomicReference for intrinsics and also to keep memory overhead low.
private final class Entries extends AtomicReference> implements Runnable {
private final String hostname;
// Needs to be package-private to be able to access it via the AtomicReferenceFieldUpdater
volatile ScheduledFuture expirationFuture;
Entries(String hostname) {
super(Collections.emptyList());
this.hostname = hostname;
}
void add(E e, int ttl, EventLoop loop) {
if (!shouldReplaceAll(e)) {
for (;;) {
List entries = get();
if (!entries.isEmpty()) {
final E firstEntry = entries.get(0);
if (shouldReplaceAll(firstEntry)) {
assert entries.size() == 1;
if (compareAndSet(entries, singletonList(e))) {
scheduleCacheExpirationIfNeeded(ttl, loop);
return;
} else {
// Need to try again as CAS failed
continue;
}
}
// Create a new List for COW semantics
List newEntries = new ArrayList(entries.size() + 1);
int i = 0;
E replacedEntry = null;
do {
E entry = entries.get(i);
// Only add old entry if the address is not the same as the one we try to add as well.
// In this case we will skip it and just add the new entry as this may have
// more up-to-date data and cancel the old after we were able to update the cache.
if (!Cache.this.equals(e, entry)) {
newEntries.add(entry);
} else {
replacedEntry = entry;
newEntries.add(e);
++i;
for (; i < entries.size(); ++i) {
newEntries.add(entries.get(i));
}
break;
}
} while (++i < entries.size());
if (replacedEntry == null) {
newEntries.add(e);
}
sortEntries(hostname, newEntries);
if (compareAndSet(entries, Collections.unmodifiableList(newEntries))) {
scheduleCacheExpirationIfNeeded(ttl, loop);
return;
}
} else if (compareAndSet(entries, singletonList(e))) {
scheduleCacheExpirationIfNeeded(ttl, loop);
return;
}
}
} else {
set(singletonList(e));
scheduleCacheExpirationIfNeeded(ttl, loop);
}
}
private void scheduleCacheExpirationIfNeeded(int ttl, EventLoop loop) {
for (;;) {
// We currently don't calculate a new TTL when we need to retry the CAS as we don't expect this to
// be invoked very concurrently and also we use SECONDS anyway. If this ever becomes a problem
// we can reconsider.
ScheduledFuture oldFuture = FUTURE_UPDATER.get(this);
if (oldFuture == null || oldFuture.getDelay(TimeUnit.SECONDS) > ttl) {
ScheduledFuture newFuture = loop.schedule(this, ttl, TimeUnit.SECONDS);
// It is possible that
// 1. task will fire in between this line, or
// 2. multiple timers may be set if there is concurrency
// (1) Shouldn't be a problem because we will fail the CAS and then the next loop will see CANCELLED
// so the ttl will not be less, and we will bail out of the loop.
// (2) This is a trade-off to avoid concurrency resulting in contention on a synchronized block.
if (FUTURE_UPDATER.compareAndSet(this, oldFuture, newFuture)) {
if (oldFuture != null) {
oldFuture.cancel(true);
}
break;
} else {
// There was something else scheduled in the meantime... Cancel and try again.
newFuture.cancel(true);
}
} else {
break;
}
}
}
boolean clearAndCancel() {
List entries = getAndSet(Collections.emptyList());
if (entries.isEmpty()) {
return false;
}
ScheduledFuture expirationFuture = FUTURE_UPDATER.getAndSet(this, CANCELLED);
if (expirationFuture != null) {
expirationFuture.cancel(false);
}
return true;
}
@Override
public void run() {
// We always remove all entries for a hostname once one entry expire. This is not the
// most efficient to do but this way we can guarantee that if a DnsResolver
// be configured to prefer one ip family over the other we will not return unexpected
// results to the enduser if one of the A or AAAA records has different TTL settings.
//
// As a TTL is just a hint of the maximum time a cache is allowed to cache stuff it's
// completely fine to remove the entry even if the TTL is not reached yet.
//
// See https://github.com/netty/netty/issues/7329
resolveCache.remove(hostname, this);
clearAndCancel();
}
}
}
