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/*
* 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 io.grpc.internal;
import static com.google.common.base.Preconditions.checkNotNull;
import static io.grpc.ConnectivityState.CONNECTING;
import static io.grpc.ConnectivityState.IDLE;
import static io.grpc.ConnectivityState.READY;
import static io.grpc.ConnectivityState.SHUTDOWN;
import static io.grpc.ConnectivityState.TRANSIENT_FAILURE;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.MoreObjects;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Lists;
import io.grpc.Attributes;
import io.grpc.ConnectivityState;
import io.grpc.ConnectivityStateInfo;
import io.grpc.EquivalentAddressGroup;
import io.grpc.LoadBalancer;
import io.grpc.Status;
import io.grpc.SynchronizationContext;
import io.grpc.SynchronizationContext.ScheduledHandle;
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.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.annotation.Nullable;
/**
* A {@link LoadBalancer} that provides no load-balancing over the addresses from the {@link
* io.grpc.NameResolver}. The channel's default behavior is used, which is walking down the address
* list and sticking to the first that works.
*/
final class PickFirstLeafLoadBalancer extends LoadBalancer {
private static final Logger log = Logger.getLogger(PickFirstLeafLoadBalancer.class.getName());
@VisibleForTesting
static final int CONNECTION_DELAY_INTERVAL_MS = 250;
private final Helper helper;
private final Map subchannels = new HashMap<>();
private Index addressIndex;
private int numTf = 0;
private boolean firstPass = true;
@Nullable
private ScheduledHandle scheduleConnectionTask;
private ConnectivityState rawConnectivityState = IDLE;
private ConnectivityState concludedState = IDLE;
private final boolean enableHappyEyeballs =
PickFirstLoadBalancerProvider.isEnabledHappyEyeballs();
PickFirstLeafLoadBalancer(Helper helper) {
this.helper = checkNotNull(helper, "helper");
}
@Override
public Status acceptResolvedAddresses(ResolvedAddresses resolvedAddresses) {
if (rawConnectivityState == SHUTDOWN) {
return Status.FAILED_PRECONDITION.withDescription("Already shut down");
}
List servers = resolvedAddresses.getAddresses();
// Validate the address list
if (servers.isEmpty()) {
Status unavailableStatus = Status.UNAVAILABLE.withDescription(
"NameResolver returned no usable address. addrs=" + resolvedAddresses.getAddresses()
+ ", attrs=" + resolvedAddresses.getAttributes());
handleNameResolutionError(unavailableStatus);
return unavailableStatus;
}
for (EquivalentAddressGroup eag : servers) {
if (eag == null) {
Status unavailableStatus = Status.UNAVAILABLE.withDescription(
"NameResolver returned address list with null endpoint. addrs="
+ resolvedAddresses.getAddresses() + ", attrs="
+ resolvedAddresses.getAttributes());
handleNameResolutionError(unavailableStatus);
return unavailableStatus;
}
}
// Since we have a new set of addresses, we are again at first pass
firstPass = true;
List cleanServers = deDupAddresses(servers);
// 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) {
Collections.shuffle(cleanServers,
config.randomSeed != null ? new Random(config.randomSeed) : new Random());
}
}
final ImmutableList newImmutableAddressGroups =
ImmutableList.builder().addAll(cleanServers).build();
if (addressIndex == null) {
addressIndex = new Index(newImmutableAddressGroups);
} else if (rawConnectivityState == READY) {
// If the previous 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)) {
SubchannelData subchannelData = subchannels.get(previousAddress);
subchannelData.getSubchannel().updateAddresses(addressIndex.getCurrentEagAsList());
return Status.OK;
} else {
addressIndex.reset(); // Previous ready subchannel not in the new list of addresses
}
} else {
addressIndex.updateGroups(newImmutableAddressGroups);
}
// remove old subchannels that were not in new address list
Set oldAddrs = new HashSet<>(subchannels.keySet());
// Flatten the new EAGs addresses
Set newAddrs = new HashSet<>();
for (EquivalentAddressGroup endpoint : newImmutableAddressGroups) {
newAddrs.addAll(endpoint.getAddresses());
}
// Shut them down and remove them
for (SocketAddress oldAddr : oldAddrs) {
if (!newAddrs.contains(oldAddr)) {
subchannels.remove(oldAddr).getSubchannel().shutdown();
}
}
if (oldAddrs.size() == 0 || rawConnectivityState == CONNECTING
|| rawConnectivityState == READY) {
// start connection attempt at first address
rawConnectivityState = CONNECTING;
updateBalancingState(CONNECTING, new Picker(PickResult.withNoResult()));
cancelScheduleTask();
requestConnection();
} else if (rawConnectivityState == IDLE) {
// start connection attempt at first address when requested
SubchannelPicker picker = new RequestConnectionPicker(this);
updateBalancingState(IDLE, picker);
} else if (rawConnectivityState == TRANSIENT_FAILURE) {
// start connection attempt at first address
cancelScheduleTask();
requestConnection();
}
return Status.OK;
}
private static List deDupAddresses(List groups) {
Set seenAddresses = new HashSet<>();
List newGroups = new ArrayList<>();
for (EquivalentAddressGroup group : groups) {
List addrs = new ArrayList<>();
for (SocketAddress addr : group.getAddresses()) {
if (seenAddresses.add(addr)) {
addrs.add(addr);
}
}
if (!addrs.isEmpty()) {
newGroups.add(new EquivalentAddressGroup(addrs, group.getAttributes()));
}
}
return newGroups;
}
@Override
public void handleNameResolutionError(Status error) {
if (rawConnectivityState == SHUTDOWN) {
return;
}
for (SubchannelData subchannelData : subchannels.values()) {
subchannelData.getSubchannel().shutdown();
}
subchannels.clear();
if (addressIndex != null) {
addressIndex.updateGroups(null);
}
rawConnectivityState = TRANSIENT_FAILURE;
updateBalancingState(TRANSIENT_FAILURE, new Picker(PickResult.withError(error)));
}
void processSubchannelState(Subchannel subchannel, ConnectivityStateInfo stateInfo) {
ConnectivityState newState = stateInfo.getState();
SubchannelData subchannelData = subchannels.get(getAddress(subchannel));
// Shutdown channels/previously relevant subchannels can still callback with state updates.
// To prevent pickers from returning these obsolete subchannels, this logic
// is included to check if the current list of active subchannels includes this subchannel.
if (subchannelData == null || subchannelData.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.
subchannelData.updateState(newState);
if (rawConnectivityState == TRANSIENT_FAILURE || concludedState == 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();
rawConnectivityState = IDLE;
updateBalancingState(IDLE, new RequestConnectionPicker(this));
break;
case CONNECTING:
rawConnectivityState = CONNECTING;
updateBalancingState(CONNECTING, new Picker(PickResult.withNoResult()));
break;
case READY:
shutdownRemaining(subchannelData);
addressIndex.seekTo(getAddress(subchannel));
rawConnectivityState = READY;
updateHealthCheckedState(subchannelData);
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) {
if (addressIndex.increment()) {
cancelScheduleTask();
requestConnection(); // is recursive so might hit the end of the addresses
}
}
if (isPassComplete()) {
rawConnectivityState = TRANSIENT_FAILURE;
updateBalancingState(TRANSIENT_FAILURE,
new Picker(PickResult.withError(stateInfo.getStatus())));
// Refresh Name Resolution, but only when all 3 conditions are met
// * We are at the end of addressIndex
// * have had status reported for all subchannels.
// * And one of the following conditions:
// * Have had enough TF reported since we completed first pass
// * Just completed the first pass
if (++numTf >= addressIndex.size() || firstPass) {
firstPass = false;
numTf = 0;
helper.refreshNameResolution();
}
}
break;
default:
throw new IllegalArgumentException("Unsupported state:" + newState);
}
}
private void updateHealthCheckedState(SubchannelData subchannelData) {
if (subchannelData.state != READY) {
return;
}
if (subchannelData.getHealthState() == READY) {
updateBalancingState(READY,
new FixedResultPicker(PickResult.withSubchannel(subchannelData.subchannel)));
} else if (subchannelData.getHealthState() == TRANSIENT_FAILURE) {
updateBalancingState(TRANSIENT_FAILURE, new Picker(PickResult.withError(
subchannelData.healthListener.healthStateInfo.getStatus())));
} else if (concludedState != TRANSIENT_FAILURE) {
updateBalancingState(subchannelData.getHealthState(),
new Picker(PickResult.withNoResult()));
}
}
private void updateBalancingState(ConnectivityState state, SubchannelPicker picker) {
// an optimization: de-dup IDLE or CONNECTING notification.
if (state == concludedState && (state == IDLE || state == CONNECTING)) {
return;
}
concludedState = state;
helper.updateBalancingState(state, picker);
}
@Override
public void shutdown() {
log.log(Level.FINE,
"Shutting down, currently have {} subchannels created", subchannels.size());
rawConnectivityState = SHUTDOWN;
concludedState = SHUTDOWN;
cancelScheduleTask();
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(SubchannelData activeSubchannelData) {
cancelScheduleTask();
for (SubchannelData subchannelData : subchannels.values()) {
if (!subchannelData.getSubchannel().equals(activeSubchannelData.subchannel)) {
subchannelData.getSubchannel().shutdown();
}
}
subchannels.clear();
activeSubchannelData.updateState(READY);
subchannels.put(getAddress(activeSubchannelData.subchannel), activeSubchannelData);
}
/**
* Requests a connection to the next applicable address' subchannel, creating one if necessary.
* Schedules a connection to next address in list as well.
* If the current channel has already attempted a connection, we attempt a connection
* to the next address/subchannel in our list. We assume that createNewSubchannel will never
* return null.
*/
@Override
public void requestConnection() {
if (addressIndex == null || !addressIndex.isValid() || rawConnectivityState == SHUTDOWN ) {
return;
}
Subchannel subchannel;
SocketAddress currentAddress;
currentAddress = addressIndex.getCurrentAddress();
subchannel = subchannels.containsKey(currentAddress)
? subchannels.get(currentAddress).getSubchannel()
: createNewSubchannel(currentAddress, addressIndex.getCurrentEagAttributes());
ConnectivityState subchannelState = subchannels.get(currentAddress).getState();
switch (subchannelState) {
case IDLE:
subchannel.requestConnection();
subchannels.get(currentAddress).updateState(CONNECTING);
scheduleNextConnection();
break;
case CONNECTING:
if (enableHappyEyeballs) {
scheduleNextConnection();
} else {
subchannel.requestConnection();
}
break;
case TRANSIENT_FAILURE:
addressIndex.increment();
requestConnection();
break;
case READY: // Shouldn't ever happen
log.warning("Requesting a connection even though we have a READY subchannel");
break;
case SHUTDOWN:
default:
// Makes checkstyle happy
}
}
/**
* Happy Eyeballs
* Schedules connection attempt to happen after a delay to the next available address.
*/
private void scheduleNextConnection() {
if (!enableHappyEyeballs
|| (scheduleConnectionTask != null && scheduleConnectionTask.isPending())) {
return;
}
class StartNextConnection implements Runnable {
@Override
public void run() {
scheduleConnectionTask = null;
if (addressIndex.increment()) {
requestConnection();
}
}
}
SynchronizationContext synchronizationContext = null;
try {
synchronizationContext = helper.getSynchronizationContext();
} catch (NullPointerException e) {
// All helpers should have a sync context, but if one doesn't (ex. user had a custom test)
// we don't want to break previously working functionality.
return;
}
scheduleConnectionTask = synchronizationContext.schedule(
new StartNextConnection(),
CONNECTION_DELAY_INTERVAL_MS,
TimeUnit.MILLISECONDS,
helper.getScheduledExecutorService());
}
private void cancelScheduleTask() {
if (scheduleConnectionTask != null) {
scheduleConnectionTask.cancel();
scheduleConnectionTask = null;
}
}
private Subchannel createNewSubchannel(SocketAddress addr, Attributes attrs) {
HealthListener hcListener = new HealthListener();
final Subchannel subchannel = helper.createSubchannel(
CreateSubchannelArgs.newBuilder()
.setAddresses(Lists.newArrayList(
new EquivalentAddressGroup(addr, attrs)))
.addOption(HEALTH_CONSUMER_LISTENER_ARG_KEY, hcListener)
.build());
if (subchannel == null) {
log.warning("Was not able to create subchannel for " + addr);
throw new IllegalStateException("Can't create subchannel");
}
SubchannelData subchannelData = new SubchannelData(subchannel, IDLE, hcListener);
hcListener.subchannelData = subchannelData;
subchannels.put(addr, subchannelData);
Attributes scAttrs = subchannel.getAttributes();
if (scAttrs.get(LoadBalancer.HAS_HEALTH_PRODUCER_LISTENER_KEY) == null) {
hcListener.healthStateInfo = ConnectivityStateInfo.forNonError(READY);
}
subchannel.start(stateInfo -> processSubchannelState(subchannel, stateInfo));
return subchannel;
}
private boolean isPassComplete() {
if (addressIndex == null || addressIndex.isValid()
|| subchannels.size() < addressIndex.size()) {
return false;
}
for (SubchannelData sc : subchannels.values()) {
if (!sc.isCompletedConnectivityAttempt() ) {
return false;
}
}
return true;
}
private final class HealthListener implements SubchannelStateListener {
private ConnectivityStateInfo healthStateInfo = ConnectivityStateInfo.forNonError(IDLE);
private SubchannelData subchannelData;
@Override
public void onSubchannelState(ConnectivityStateInfo newState) {
log.log(Level.FINE, "Received health status {0} for subchannel {1}",
new Object[]{newState, subchannelData.subchannel});
healthStateInfo = newState;
try {
SubchannelData curSubChanData = subchannels.get(addressIndex.getCurrentAddress());
if (curSubChanData != null && curSubChanData.healthListener == this) {
updateHealthCheckedState(subchannelData);
}
} catch (IllegalStateException e) {
log.fine("Health listener received state change after subchannel was removed");
}
}
}
private SocketAddress getAddress(Subchannel subchannel) {
return subchannel.getAddresses().getAddresses().get(0);
}
@VisibleForTesting
ConnectivityState getConcludedConnectivityState() {
return this.concludedState;
}
/**
* 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(pickFirstLeafLoadBalancer::requestConnection);
}
return PickResult.withNoResult();
}
}
/**
* Index as in 'i', the pointer to an entry. Not a "search index."
* All updates should be done in a synchronization context.
*/
@VisibleForTesting
static final class Index {
private List addressGroups;
private int groupIndex;
private int addressIndex;
public Index(List groups) {
this.addressGroups = groups != null ? groups : Collections.emptyList();
}
public boolean isValid() {
// Is invalid if empty or has incremented off the end
return groupIndex < addressGroups.size();
}
public boolean isAtBeginning() {
return groupIndex == 0 && addressIndex == 0;
}
/**
* Move to next address in group. If last address in group move to first address of next group.
* @return false if went off end of the list, otherwise true
*/
public boolean increment() {
if (!isValid()) {
return false;
}
EquivalentAddressGroup group = addressGroups.get(groupIndex);
addressIndex++;
if (addressIndex >= group.getAddresses().size()) {
groupIndex++;
addressIndex = 0;
return groupIndex < addressGroups.size();
}
return true;
}
public void reset() {
groupIndex = 0;
addressIndex = 0;
}
public SocketAddress getCurrentAddress() {
if (!isValid()) {
throw new IllegalStateException("Index is past the end of the address group list");
}
return addressGroups.get(groupIndex).getAddresses().get(addressIndex);
}
public Attributes getCurrentEagAttributes() {
if (!isValid()) {
throw new IllegalStateException("Index is off the end of the address group list");
}
return addressGroups.get(groupIndex).getAttributes();
}
public List getCurrentEagAsList() {
return Collections.singletonList(
new EquivalentAddressGroup(getCurrentAddress(), getCurrentEagAttributes()));
}
/**
* Update to new groups, resetting the current index.
*/
public void updateGroups(ImmutableList newGroups) {
addressGroups = newGroups != null ? newGroups : Collections.emptyList();
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;
}
public int size() {
return (addressGroups != null) ? addressGroups.size() : 0;
}
}
private static final class SubchannelData {
private final Subchannel subchannel;
private ConnectivityState state;
private final HealthListener healthListener;
private boolean completedConnectivityAttempt = false;
public SubchannelData(Subchannel subchannel, ConnectivityState state,
HealthListener subchannelHealthListener) {
this.subchannel = subchannel;
this.state = state;
this.healthListener = subchannelHealthListener;
}
public Subchannel getSubchannel() {
return this.subchannel;
}
public ConnectivityState getState() {
return this.state;
}
public boolean isCompletedConnectivityAttempt() {
return completedConnectivityAttempt;
}
private void updateState(ConnectivityState newState) {
this.state = newState;
if (newState == READY || newState == TRANSIENT_FAILURE) {
completedConnectivityAttempt = true;
} else if (newState == IDLE) {
completedConnectivityAttempt = false;
}
}
private ConnectivityState getHealthState() {
return healthListener.healthStateInfo.getState();
}
}
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;
}
}
}
