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RoundRobinLoadBalancer.java
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RoundRobinLoadBalancer.java
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/*
* Copyright 2016 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.util;
import static com.google.common.base.Preconditions.checkArgument;
import static io.grpc.ConnectivityState.CONNECTING;
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 com.google.common.base.MoreObjects;
import com.google.common.base.Preconditions;
import io.grpc.ConnectivityState;
import io.grpc.EquivalentAddressGroup;
import io.grpc.Internal;
import io.grpc.LoadBalancer;
import io.grpc.NameResolver;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.List;
import java.util.Random;
import java.util.concurrent.atomic.AtomicInteger;
/**
* A {@link LoadBalancer} that provides round-robin load-balancing over the {@link
* EquivalentAddressGroup}s from the {@link NameResolver}.
*/
@Internal
public class RoundRobinLoadBalancer extends MultiChildLoadBalancer {
private final AtomicInteger sequence = new AtomicInteger(new Random().nextInt());
protected SubchannelPicker currentPicker = new EmptyPicker();
public RoundRobinLoadBalancer(Helper helper) {
super(helper);
}
/**
* Updates picker with the list of active subchannels (state == READY).
*/
@Override
protected void updateOverallBalancingState() {
List<ChildLbState> activeList = getReadyChildren();
if (activeList.isEmpty()) {
// No READY subchannels
// RRLB will request connection immediately on subchannel IDLE.
boolean isConnecting = false;
for (ChildLbState childLbState : getChildLbStates()) {
ConnectivityState state = childLbState.getCurrentState();
if (state == CONNECTING || state == IDLE) {
isConnecting = true;
break;
}
}
if (isConnecting) {
updateBalancingState(CONNECTING, new EmptyPicker());
} else {
updateBalancingState(TRANSIENT_FAILURE, createReadyPicker(getChildLbStates()));
}
} else {
updateBalancingState(READY, createReadyPicker(activeList));
}
}
private void updateBalancingState(ConnectivityState state, SubchannelPicker picker) {
if (state != currentConnectivityState || !picker.equals(currentPicker)) {
getHelper().updateBalancingState(state, picker);
currentConnectivityState = state;
currentPicker = picker;
}
}
protected SubchannelPicker createReadyPicker(Collection<ChildLbState> children) {
List<SubchannelPicker> pickerList = new ArrayList<>();
for (ChildLbState child : children) {
SubchannelPicker picker = child.getCurrentPicker();
pickerList.add(picker);
}
return new ReadyPicker(pickerList, sequence);
}
@VisibleForTesting
static class ReadyPicker extends SubchannelPicker {
private final List<SubchannelPicker> subchannelPickers; // non-empty
private final AtomicInteger index;
private final int hashCode;
public ReadyPicker(List<SubchannelPicker> list, AtomicInteger index) {
checkArgument(!list.isEmpty(), "empty list");
this.subchannelPickers = list;
this.index = Preconditions.checkNotNull(index, "index");
// Every created picker is checked for equality in updateBalancingState() at least once.
// Pre-compute the hash so it can be checked cheaply. Using the hash in equals() makes it very
// fast except when the pickers are (very likely) equal.
//
// For equality we treat children as a set; use hash code as defined by Set
int sum = 0;
for (SubchannelPicker picker : subchannelPickers) {
sum += picker.hashCode();
}
this.hashCode = sum;
}
@Override
public PickResult pickSubchannel(PickSubchannelArgs args) {
return subchannelPickers.get(nextIndex()).pickSubchannel(args);
}
@Override
public String toString() {
return MoreObjects.toStringHelper(ReadyPicker.class)
.add("subchannelPickers", subchannelPickers)
.toString();
}
private int nextIndex() {
int i = index.getAndIncrement() & Integer.MAX_VALUE;
return i % subchannelPickers.size();
}
@VisibleForTesting
List<SubchannelPicker> getSubchannelPickers() {
return subchannelPickers;
}
@Override
public int hashCode() {
return hashCode;
}
@Override
public boolean equals(Object o) {
if (!(o instanceof ReadyPicker)) {
return false;
}
ReadyPicker other = (ReadyPicker) o;
if (other == this) {
return true;
}
// the lists cannot contain duplicate subchannels
return hashCode == other.hashCode
&& index == other.index
&& subchannelPickers.size() == other.subchannelPickers.size()
&& new HashSet<>(subchannelPickers).containsAll(other.subchannelPickers);
}
}
@VisibleForTesting
static final class EmptyPicker extends SubchannelPicker {
@Override
public PickResult pickSubchannel(PickSubchannelArgs args) {
return PickResult.withNoResult();
}
@Override
public int hashCode() {
return getClass().hashCode();
}
@Override
public boolean equals(Object o) {
return o instanceof EmptyPicker;
}
}
}