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The official Couchbase JVM Core IO Library
/*
* Copyright 2023 The gRPC Authors
*
* Licensed 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 com.couchbase.client.core.deps.io.grpc.internal;
import static com.couchbase.client.core.deps.com.google.common.base.Preconditions.checkNotNull;
import static com.couchbase.client.core.deps.io.grpc.ConnectivityState.CONNECTING;
import static com.couchbase.client.core.deps.io.grpc.ConnectivityState.IDLE;
import static com.couchbase.client.core.deps.io.grpc.ConnectivityState.READY;
import static com.couchbase.client.core.deps.io.grpc.ConnectivityState.SHUTDOWN;
import static com.couchbase.client.core.deps.io.grpc.ConnectivityState.TRANSIENT_FAILURE;
import com.couchbase.client.core.deps.com.google.common.annotations.VisibleForTesting;
import com.couchbase.client.core.deps.com.google.common.base.MoreObjects;
import com.couchbase.client.core.deps.com.google.common.collect.Lists;
import com.couchbase.client.core.deps.io.grpc.Attributes;
import com.couchbase.client.core.deps.io.grpc.ConnectivityState;
import com.couchbase.client.core.deps.io.grpc.ConnectivityStateInfo;
import com.couchbase.client.core.deps.io.grpc.EquivalentAddressGroup;
import com.couchbase.client.core.deps.io.grpc.ExperimentalApi;
import com.couchbase.client.core.deps.io.grpc.LoadBalancer;
import com.couchbase.client.core.deps.io.grpc.Status;
import java.net.SocketAddress;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Random;
import java.util.Set;
import java.util.concurrent.atomic.AtomicBoolean;
import javax.annotation.Nullable;
/**
* A {@link LoadBalancer} that provides no load-balancing over the addresses from the {@link
* com.couchbase.client.core.deps.io.grpc.NameResolver}. The channel's default behavior is used, which is walking down the address
* list and sticking to the first that works.
*/
@ExperimentalApi("https://github.com/grpc/grpc-java/issues/10383")
final class PickFirstLeafLoadBalancer extends LoadBalancer {
private final Helper helper;
private final Map subchannels = new HashMap<>();
private Index addressIndex;
private ConnectivityState currentState = IDLE;
PickFirstLeafLoadBalancer(Helper helper) {
this.helper = checkNotNull(helper, "helper");
}
@Override
public boolean acceptResolvedAddresses(ResolvedAddresses resolvedAddresses) {
List servers = resolvedAddresses.getAddresses();
if (servers.isEmpty()) {
handleNameResolutionError(Status.UNAVAILABLE.withDescription(
"NameResolver returned no usable address. addrs=" + resolvedAddresses.getAddresses()
+ ", attrs=" + resolvedAddresses.getAttributes()));
return false;
}
for (EquivalentAddressGroup eag : servers) {
if (eag == null) {
handleNameResolutionError(Status.UNAVAILABLE.withDescription(
"NameResolver returned address list with null endpoint. addrs="
+ resolvedAddresses.getAddresses() + ", attrs=" + resolvedAddresses.getAttributes()));
return false;
}
}
// We can optionally be configured to shuffle the address list. This can help better distribute
// the load.
if (resolvedAddresses.getLoadBalancingPolicyConfig()
instanceof PickFirstLeafLoadBalancerConfig) {
PickFirstLeafLoadBalancerConfig config
= (PickFirstLeafLoadBalancerConfig) resolvedAddresses.getLoadBalancingPolicyConfig();
if (config.shuffleAddressList != null && config.shuffleAddressList) {
servers = new ArrayList(servers);
Collections.shuffle(servers,
config.randomSeed != null ? new Random(config.randomSeed) : new Random());
}
}
final List newImmutableAddressGroups =
Collections.unmodifiableList(new ArrayList<>(servers));
if (addressIndex == null) {
addressIndex = new Index(newImmutableAddressGroups);
} else if (currentState == READY) {
// If a ready subchannel exists in new address list,
// keep this connection and don't create new subchannels
SocketAddress previousAddress = addressIndex.getCurrentAddress();
addressIndex.updateGroups(newImmutableAddressGroups);
if (addressIndex.seekTo(previousAddress)) {
return true;
}
addressIndex.reset();
} else {
addressIndex.updateGroups(newImmutableAddressGroups);
}
// Create subchannels for all new addresses, preserving existing connections
Set oldAddrs = new HashSet<>(subchannels.keySet());
Set newAddrs = new HashSet<>();
for (EquivalentAddressGroup endpoint : newImmutableAddressGroups) {
for (SocketAddress addr : endpoint.getAddresses()) {
newAddrs.add(addr);
if (!subchannels.containsKey(addr)) {
createNewSubchannel(addr);
}
}
}
// remove old subchannels that were not in new address list
for (SocketAddress oldAddr : oldAddrs) {
if (!newAddrs.contains(oldAddr)) {
subchannels.get(oldAddr).getSubchannel().shutdown();
subchannels.remove(oldAddr);
}
}
if (oldAddrs.size() == 0 || currentState == CONNECTING || currentState == READY) {
// start connection attempt at first address
updateBalancingState(CONNECTING, new Picker(PickResult.withNoResult()));
requestConnection();
} else if (currentState == IDLE) {
// start connection attempt at first address when requested
SubchannelPicker picker = new RequestConnectionPicker(this);
updateBalancingState(IDLE, picker);
} else if (currentState == TRANSIENT_FAILURE) {
// start connection attempt at first address
requestConnection();
}
return true;
}
@Override
public void handleNameResolutionError(Status error) {
for (SubchannelData subchannelData : subchannels.values()) {
subchannelData.getSubchannel().shutdown();
}
subchannels.clear();
// NB(lukaszx0) Whether we should propagate the error unconditionally is arguable. It's fine
// for time being.
updateBalancingState(TRANSIENT_FAILURE, new Picker(PickResult.withError(error)));
}
void processSubchannelState(Subchannel subchannel, ConnectivityStateInfo stateInfo) {
ConnectivityState newState = stateInfo.getState();
// Shutdown channels/previously relevant subchannels can still callback with state updates.
// To prevent pickers from returning these obselete subchannels, this logic
// is included to check if the current list of active subchannels includes this subchannel.
if (!subchannels.containsKey(getAddress(subchannel))
|| subchannels.get(getAddress(subchannel)).getSubchannel() != subchannel) {
return;
}
if (newState == SHUTDOWN) {
return;
}
if (newState == IDLE) {
helper.refreshNameResolution();
}
// If we are transitioning from a TRANSIENT_FAILURE to CONNECTING or IDLE we ignore this state
// transition and still keep the LB in TRANSIENT_FAILURE state. This is referred to as "sticky
// transient failure". Only a subchannel state change to READY will get the LB out of
// TRANSIENT_FAILURE. If the state is IDLE we additionally request a new connection so that we
// keep retrying for a connection.
// With the new pick first implementation, individual subchannels will have their own backoff
// on a per-address basis. Thus, iterative requests for connections will not be requested
// once the first pass through is complete.
// However, every time there is an address update, we will perform a pass through for the new
// addresses in the updated list.
subchannels.get(getAddress(subchannel)).updateState(newState);
if (currentState == TRANSIENT_FAILURE) {
if (newState == CONNECTING) {
// each subchannel is responsible for its own backoff
return;
} else if (newState == IDLE) {
requestConnection();
return;
}
}
switch (newState) {
case IDLE:
// Shutdown when ready: connect from beginning when prompted
addressIndex.reset();
updateBalancingState(IDLE, new RequestConnectionPicker(this));;
break;
case CONNECTING:
// It's safe to use RequestConnectionPicker here, so when coming from IDLE we could leave
// the current picker in-place. But ignoring the potential optimization is simpler.
updateBalancingState(CONNECTING, new Picker(PickResult.withNoResult()));
break;
case READY:
updateBalancingState(READY, new Picker(PickResult.withSubchannel(subchannel)));
shutdownRemaining(subchannel);
addressIndex.seekTo(getAddress(subchannel));
break;
case TRANSIENT_FAILURE:
// If we are looking at current channel, request a connection if possible
if (addressIndex.isValid()
&& subchannels.get(addressIndex.getCurrentAddress()).getSubchannel() == subchannel) {
addressIndex.increment();
requestConnection();
// If no addresses remaining, go into TRANSIENT_FAILURE
if (!addressIndex.isValid()) {
helper.refreshNameResolution();
updateBalancingState(TRANSIENT_FAILURE,
new Picker(PickResult.withError(stateInfo.getStatus())));
}
}
break;
default:
throw new IllegalArgumentException("Unsupported state:" + newState);
}
}
private void updateBalancingState(ConnectivityState state, SubchannelPicker picker) {
if (state != currentState || state == READY || state == TRANSIENT_FAILURE) {
currentState = state;
helper.updateBalancingState(state, picker);
}
}
@Override
public void shutdown() {
for (SubchannelData subchannelData : subchannels.values()) {
subchannelData.getSubchannel().shutdown();
}
subchannels.clear();
}
/**
* Shuts down remaining subchannels. Called when a subchannel becomes ready, which means
* that all other subchannels must be shutdown.
*/
private void shutdownRemaining(Subchannel activeSubchannel) {
for (SubchannelData subchannelData : subchannels.values()) {
if (!subchannelData.getSubchannel().equals(activeSubchannel)) {
subchannelData.getSubchannel().shutdown();
}
}
subchannels.clear();
subchannels.put(getAddress(activeSubchannel), new SubchannelData(activeSubchannel, READY));
}
/**
* Requests a connection to the next applicable address' subchannel, creating one if necessary
* If the current channel has already attempted a connection, we attempt a connection
* to the next address/subchannel in our list.
*/
@Override
public void requestConnection() {
if (subchannels.size() == 0) {
return;
}
if (addressIndex.isValid()) {
Subchannel subchannel = subchannels.containsKey(addressIndex.getCurrentAddress())
? subchannels.get(addressIndex.getCurrentAddress()).getSubchannel()
: createNewSubchannel(addressIndex.getCurrentAddress());
ConnectivityState subchannelState =
subchannels.get(addressIndex.getCurrentAddress()).getState();
if (subchannelState == IDLE) {
subchannel.requestConnection();
} else if (subchannelState == CONNECTING || subchannelState == TRANSIENT_FAILURE) {
addressIndex.increment();
requestConnection();
}
}
}
private Subchannel createNewSubchannel(SocketAddress addr) {
final Subchannel subchannel = helper.createSubchannel(
CreateSubchannelArgs.newBuilder()
.setAddresses(Lists.newArrayList(
new EquivalentAddressGroup(addr)))
.build());
subchannels.put(addr, new SubchannelData(subchannel, IDLE));
subchannel.start(new SubchannelStateListener() {
@Override
public void onSubchannelState(ConnectivityStateInfo stateInfo) {
processSubchannelState(subchannel, stateInfo);
}
});
return subchannel;
}
private SocketAddress getAddress(Subchannel subchannel) {
return subchannel.getAddresses().getAddresses().get(0);
}
@VisibleForTesting
ConnectivityState getCurrentState() {
return this.currentState;
}
/**
* No-op picker which doesn't add any custom picking logic. It just passes already known result
* received in constructor.
*/
private static final class Picker extends SubchannelPicker {
private final PickResult result;
Picker(PickResult result) {
this.result = checkNotNull(result, "result");
}
@Override
public PickResult pickSubchannel(PickSubchannelArgs args) {
return result;
}
@Override
public String toString() {
return MoreObjects.toStringHelper(Picker.class).add("result", result).toString();
}
}
/**
* Picker that requests connection during the first pick, and returns noResult.
*/
private final class RequestConnectionPicker extends SubchannelPicker {
private final PickFirstLeafLoadBalancer pickFirstLeafLoadBalancer;
private final AtomicBoolean connectionRequested = new AtomicBoolean(false);
RequestConnectionPicker(PickFirstLeafLoadBalancer pickFirstLeafLoadBalancer) {
this.pickFirstLeafLoadBalancer =
checkNotNull(pickFirstLeafLoadBalancer, "pickFirstLeafLoadBalancer");
}
@Override
public PickResult pickSubchannel(PickSubchannelArgs args) {
if (connectionRequested.compareAndSet(false, true)) {
helper.getSynchronizationContext().execute(new Runnable() {
@Override
public void run() {
pickFirstLeafLoadBalancer.requestConnection();
}
});
}
return PickResult.withNoResult();
}
}
/**
* Index as in 'i', the pointer to an entry. Not a "search index."
*/
@VisibleForTesting
static final class Index {
private List addressGroups;
private int groupIndex;
private int addressIndex;
public Index(List groups) {
this.addressGroups = groups;
}
public boolean isValid() {
// addressIndex will never be invalid
return groupIndex < addressGroups.size();
}
public boolean isAtBeginning() {
return groupIndex == 0 && addressIndex == 0;
}
public void increment() {
EquivalentAddressGroup group = addressGroups.get(groupIndex);
addressIndex++;
if (addressIndex >= group.getAddresses().size()) {
groupIndex++;
addressIndex = 0;
}
}
public void reset() {
groupIndex = 0;
addressIndex = 0;
}
public SocketAddress getCurrentAddress() {
return addressGroups.get(groupIndex).getAddresses().get(addressIndex);
}
public Attributes getCurrentEagAttributes() {
return addressGroups.get(groupIndex).getAttributes();
}
public List getGroups() {
return addressGroups;
}
/**
* Update to new groups, resetting the current index.
*/
public void updateGroups(List newGroups) {
addressGroups = newGroups;
reset();
}
/**
* Returns false if the needle was not found and the current index was left unchanged.
*/
public boolean seekTo(SocketAddress needle) {
for (int i = 0; i < addressGroups.size(); i++) {
EquivalentAddressGroup group = addressGroups.get(i);
int j = group.getAddresses().indexOf(needle);
if (j == -1) {
continue;
}
this.groupIndex = i;
this.addressIndex = j;
return true;
}
return false;
}
}
private static final class SubchannelData {
private final Subchannel subchannel;
private ConnectivityState state;
public SubchannelData(Subchannel subchannel, ConnectivityState state) {
this.subchannel = subchannel;
this.state = state;
}
public Subchannel getSubchannel() {
return this.subchannel;
}
public ConnectivityState getState() {
return this.state;
}
private void updateState(ConnectivityState newState) {
this.state = newState;
}
}
public static final class PickFirstLeafLoadBalancerConfig {
@Nullable
public final Boolean shuffleAddressList;
// For testing purposes only, not meant to be parsed from a real config.
@Nullable
final Long randomSeed;
public PickFirstLeafLoadBalancerConfig(@Nullable Boolean shuffleAddressList) {
this(shuffleAddressList, null);
}
PickFirstLeafLoadBalancerConfig(@Nullable Boolean shuffleAddressList,
@Nullable Long randomSeed) {
this.shuffleAddressList = shuffleAddressList;
this.randomSeed = randomSeed;
}
}
}