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RoundRobinLoadBalancerFactory2.java
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/
RoundRobinLoadBalancerFactory2.java
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/*
* Copyright 2016, Google Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following disclaimer
* in the documentation and/or other materials provided with the
* distribution.
*
* * Neither the name of Google Inc. nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package io.grpc.util;
import static com.google.common.base.Preconditions.checkNotNull;
import static io.grpc.ConnectivityState.IDLE;
import static io.grpc.ConnectivityState.READY;
import static io.grpc.ConnectivityState.TRANSIENT_FAILURE;
import com.google.common.annotations.VisibleForTesting;
import io.grpc.Attributes;
import io.grpc.ConnectivityStateInfo;
import io.grpc.EquivalentAddressGroup;
import io.grpc.ExperimentalApi;
import io.grpc.LoadBalancer;
import io.grpc.LoadBalancer2;
import io.grpc.LoadBalancer2.PickResult;
import io.grpc.LoadBalancer2.Subchannel;
import io.grpc.LoadBalancer2.SubchannelPicker;
import io.grpc.Metadata;
import io.grpc.NameResolver;
import io.grpc.ResolvedServerInfo;
import io.grpc.ResolvedServerInfoGroup;
import io.grpc.Status;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.concurrent.atomic.AtomicReference;
import javax.annotation.Nullable;
import javax.annotation.concurrent.GuardedBy;
/**
* A {@link LoadBalancer} that provides round-robin load balancing mechanism over the
* addresses from the {@link NameResolver}. The sub-lists received from the name resolver
* are considered to be an {@link EquivalentAddressGroup} and each of these sub-lists is
* what is then balanced across.
*
* <p><strong>TECHNICAL PREVIEW: </strong>The name of this class is temporary. It will be renamed to
* {@code RoundRobinLoadBalancerFactory} during the
* <a href="https://github.com/grpc/grpc-java/issues/2656" target="_blank">transition to LBv2</a>.
* You should use it only if you want to experiment the LBv2 code path.
*/
@ExperimentalApi("https://github.com/grpc/grpc-java/issues/1771")
public class RoundRobinLoadBalancerFactory2 extends LoadBalancer2.Factory {
private static final RoundRobinLoadBalancerFactory2 INSTANCE =
new RoundRobinLoadBalancerFactory2();
private RoundRobinLoadBalancerFactory2() {
}
public static RoundRobinLoadBalancerFactory2 getInstance() {
return INSTANCE;
}
@Override
public LoadBalancer2 newLoadBalancer(LoadBalancer2.Helper helper) {
return new RoundRobinLoadBalancer(helper);
}
@VisibleForTesting
static class RoundRobinLoadBalancer extends LoadBalancer2 {
private final Helper helper;
private final Map<EquivalentAddressGroup, Subchannel> subchannels =
new HashMap<EquivalentAddressGroup, Subchannel>();
@VisibleForTesting
static final Attributes.Key<AtomicReference<ConnectivityStateInfo>> STATE_INFO =
Attributes.Key.of("state-info");
public RoundRobinLoadBalancer(Helper helper) {
this.helper = helper;
}
@Override
public void handleResolvedAddresses(List<ResolvedServerInfoGroup> servers,
Attributes attributes) {
Set<EquivalentAddressGroup> currentAddrs = subchannels.keySet();
Set<EquivalentAddressGroup> latestAddrs =
resolvedServerInfoGroupToEquivalentAddressGroup(servers);
Set<EquivalentAddressGroup> addedAddrs = setsDifference(latestAddrs, currentAddrs);
Set<EquivalentAddressGroup> removedAddrs = setsDifference(currentAddrs, latestAddrs);
// NB(lukaszx0): we don't merge `attributes` with `subchannelAttr` because subchannel doesn't
// need them. They're describing the resolved server list but we're not taking any action
// based on this information.
Attributes subchannelAttrs = Attributes.newBuilder()
// NB(lukaszx0): because attributes are immutable we can't set new value for the key
// after creation but since we can mutate the values we leverge that and set
// AtomicReference which will allow mutating state info for given channel.
.set(STATE_INFO, new AtomicReference<ConnectivityStateInfo>(
ConnectivityStateInfo.forNonError(IDLE)))
.build();
// Create new subchannels for new addresses.
for (EquivalentAddressGroup addressGroup : addedAddrs) {
Subchannel subchannel = checkNotNull(helper.createSubchannel(addressGroup, subchannelAttrs),
"subchannel");
subchannels.put(addressGroup, subchannel);
subchannel.requestConnection();
}
// Shutdown subchannels for removed addresses.
for (EquivalentAddressGroup addressGroup : removedAddrs) {
Subchannel subchannel = subchannels.remove(addressGroup);
subchannel.shutdown();
}
updatePicker(getAggregatedError());
}
@Override
public void handleNameResolutionError(Status error) {
updatePicker(error);
}
@Override
public void handleSubchannelState(Subchannel subchannel, ConnectivityStateInfo stateInfo) {
if (!subchannels.containsValue(subchannel)) {
return;
}
if (stateInfo.getState() == IDLE) {
subchannel.requestConnection();
}
getSubchannelStateInfoRef(subchannel).set(stateInfo);
updatePicker(getAggregatedError());
}
@Override
public void shutdown() {
for (Subchannel subchannel : getSubchannels()) {
subchannel.shutdown();
}
}
/**
* Updates picker with the list of active subchannels (state == READY).
*/
private void updatePicker(@Nullable Status error) {
List<Subchannel> activeList = filterNonFailingSubchannels(getSubchannels());
helper.updatePicker(new Picker(activeList, error));
}
/**
* Filters out non-ready subchannels.
*/
private static List<Subchannel> filterNonFailingSubchannels(
Collection<Subchannel> subchannels) {
List<Subchannel> readySubchannels = new ArrayList<Subchannel>(subchannels.size());
for (Subchannel subchannel : subchannels) {
if (getSubchannelStateInfoRef(subchannel).get().getState() == READY) {
readySubchannels.add(subchannel);
}
}
return readySubchannels;
}
/**
* Converts list of {@link ResolvedServerInfoGroup} to {@link EquivalentAddressGroup} set.
*/
private static Set<EquivalentAddressGroup> resolvedServerInfoGroupToEquivalentAddressGroup(
List<ResolvedServerInfoGroup> groupList) {
Set<EquivalentAddressGroup> addrs = new HashSet<EquivalentAddressGroup>();
for (ResolvedServerInfoGroup group : groupList) {
for (ResolvedServerInfo server : group.getResolvedServerInfoList()) {
addrs.add(new EquivalentAddressGroup(server.getAddress()));
}
}
return addrs;
}
/**
* If all subchannels are TRANSIENT_FAILURE, return the Status associated with an arbitrary
* subchannel otherwise, return null.
*/
@Nullable
private Status getAggregatedError() {
Status status = null;
for (Subchannel subchannel : getSubchannels()) {
ConnectivityStateInfo stateInfo = getSubchannelStateInfoRef(subchannel).get();
if (stateInfo.getState() != TRANSIENT_FAILURE) {
return null;
}
status = stateInfo.getStatus();
}
return status;
}
@VisibleForTesting
Collection<Subchannel> getSubchannels() {
return subchannels.values();
}
private static AtomicReference<ConnectivityStateInfo> getSubchannelStateInfoRef(
Subchannel subchannel) {
return checkNotNull(subchannel.getAttributes().get(STATE_INFO), "STATE_INFO");
}
private static <T> Set<T> setsDifference(Set<T> a, Set<T> b) {
Set<T> aCopy = new HashSet<T>(a);
aCopy.removeAll(b);
return aCopy;
}
}
@VisibleForTesting
static class Picker extends SubchannelPicker {
@Nullable
private final Status status;
private final List<Subchannel> list;
private final int size;
@GuardedBy("this")
private int index = 0;
Picker(List<Subchannel> list, @Nullable Status status) {
this.list = Collections.unmodifiableList(list);
this.size = list.size();
this.status = status;
}
@Override
public PickResult pickSubchannel(Attributes affinity, Metadata headers) {
if (size > 0) {
return PickResult.withSubchannel(nextSubchannel());
}
if (status != null) {
return PickResult.withError(status);
}
return PickResult.withNoResult();
}
private Subchannel nextSubchannel() {
if (size == 0) {
throw new NoSuchElementException();
}
synchronized (this) {
Subchannel val = list.get(index);
index++;
if (index >= size) {
index = 0;
}
return val;
}
}
@VisibleForTesting
List<Subchannel> getList() {
return list;
}
@VisibleForTesting
Status getStatus() {
return status;
}
}
}