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feat(xds): Add CachedChannelManager for caching channel instances
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‎xds/src/main/java/io/grpc/xds/internal/grpcservice/CachedChannelManager.java‎

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/*
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* Copyright 2026 The gRPC Authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package io.grpc.xds.internal.grpcservice;
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import static com.google.common.base.Preconditions.checkNotNull;
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import com.google.auto.value.AutoValue;
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import io.grpc.ManagedChannel;
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import io.grpc.xds.internal.grpcservice.GrpcServiceConfig.GoogleGrpcConfig;
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import java.util.concurrent.atomic.AtomicReference;
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import java.util.function.Function;
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/**
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* Concrete class managing the lifecycle of a single ManagedChannel for a GrpcServiceConfig.
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*/
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public class CachedChannelManager {
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private final Function<GrpcServiceConfig, ManagedChannel> channelCreator;
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private final Object lock = new Object();
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private final AtomicReference<ChannelHolder> channelHolder = new AtomicReference<>();
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/**
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* Default constructor for production that creates a channel using the config's target and
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* credentials.
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*/
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public CachedChannelManager() {
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this(config -> {
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GoogleGrpcConfig googleGrpc = config.googleGrpc();
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return io.grpc.Grpc.newChannelBuilder(googleGrpc.target(),
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googleGrpc.configuredChannelCredentials().channelCredentials()).build();
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});
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}
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/**
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* Constructor for testing to inject a channel creator.
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*/
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public CachedChannelManager(Function<GrpcServiceConfig, ManagedChannel> channelCreator) {
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this.channelCreator = checkNotNull(channelCreator, "channelCreator");
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}
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/**
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* Returns a ManagedChannel for the given configuration. If the target or credentials config
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* changes, the old channel is shut down and a new one is created.
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*/
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public ManagedChannel getChannel(GrpcServiceConfig config) {
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GoogleGrpcConfig googleGrpc = config.googleGrpc();
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ChannelKey newChannelKey = ChannelKey.of(
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googleGrpc.target(),
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googleGrpc.configuredChannelCredentials().channelCredsConfig());
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// 1. Fast path: Lock-free read
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ChannelHolder holder = channelHolder.get();
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if (holder != null && holder.channelKey().equals(newChannelKey)) {
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return holder.channel();
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}
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ManagedChannel oldChannel = null;
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ManagedChannel newChannel;
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// 2. Slow path: Update with locking
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synchronized (lock) {
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holder = channelHolder.get(); // Double check
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if (holder != null && holder.channelKey().equals(newChannelKey)) {
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return holder.channel();
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}
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// 3. Create inside lock to avoid creation storms
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newChannel = channelCreator.apply(config);
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ChannelHolder newHolder = ChannelHolder.create(newChannelKey, newChannel);
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if (holder != null) {
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oldChannel = holder.channel();
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}
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channelHolder.set(newHolder);
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}
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// 4. Shutdown outside lock
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if (oldChannel != null) {
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oldChannel.shutdown();
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}
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return newChannel;
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}
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/** Removes underlying resources on shutdown. */
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public void close() {
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ChannelHolder holder = channelHolder.get();
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if (holder != null) {
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holder.channel().shutdown();
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}
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}
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@AutoValue
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abstract static class ChannelKey {
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static ChannelKey of(String target, ChannelCredsConfig credentialsConfig) {
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return new AutoValue_CachedChannelManager_ChannelKey(target, credentialsConfig);
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}
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abstract String target();
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abstract ChannelCredsConfig channelCredsConfig();
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}
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@AutoValue
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abstract static class ChannelHolder {
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static ChannelHolder create(ChannelKey channelKey, ManagedChannel channel) {
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return new AutoValue_CachedChannelManager_ChannelHolder(channelKey, channel);
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}
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abstract ChannelKey channelKey();
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abstract ManagedChannel channel();
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}
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}

‎xds/src/test/java/io/grpc/xds/internal/grpcservice/CachedChannelManagerTest.java‎

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/*
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* Copyright 2026 The gRPC Authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package io.grpc.xds.internal.grpcservice;
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import static com.google.common.truth.Truth.assertThat;
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import static org.mockito.Mockito.mock;
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import static org.mockito.Mockito.verify;
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import static org.mockito.Mockito.when;
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import com.google.common.collect.ImmutableList;
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import io.grpc.ManagedChannel;
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import io.grpc.xds.internal.grpcservice.GrpcServiceConfig.GoogleGrpcConfig;
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import java.util.function.Function;
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import org.junit.Before;
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import org.junit.Rule;
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import org.junit.Test;
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import org.junit.runner.RunWith;
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import org.junit.runners.JUnit4;
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import org.mockito.Mock;
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import org.mockito.junit.MockitoJUnit;
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import org.mockito.junit.MockitoRule;
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/**
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* Unit tests for {@link CachedChannelManager}.
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*/
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@RunWith(JUnit4.class)
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public class CachedChannelManagerTest {
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@Rule
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public final MockitoRule mocks = MockitoJUnit.rule();
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@Mock
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private Function<GrpcServiceConfig, ManagedChannel> mockCreator;
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@Mock
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private ManagedChannel mockChannel1;
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@Mock
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private ManagedChannel mockChannel2;
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private CachedChannelManager manager;
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private GrpcServiceConfig config1;
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private GrpcServiceConfig config2;
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@Before
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public void setUp() {
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manager = new CachedChannelManager(mockCreator);
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config1 = buildConfig("authz.service.com", "creds1");
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config2 = buildConfig("authz.service.com", "creds2"); // Different creds instance
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}
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private GrpcServiceConfig buildConfig(String target, String credsType) {
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ChannelCredsConfig credsConfig = mock(ChannelCredsConfig.class);
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when(credsConfig.type()).thenReturn(credsType);
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ConfiguredChannelCredentials creds = ConfiguredChannelCredentials.create(
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mock(io.grpc.ChannelCredentials.class), credsConfig);
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GoogleGrpcConfig googleGrpc = GoogleGrpcConfig.builder()
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.target(target)
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.configuredChannelCredentials(creds)
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.build();
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return GrpcServiceConfig.newBuilder()
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.googleGrpc(googleGrpc)
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.initialMetadata(ImmutableList.of())
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.build();
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}
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@Test
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public void getChannel_sameConfig_returnsCached() {
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when(mockCreator.apply(config1)).thenReturn(mockChannel1);
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ManagedChannel channela = manager.getChannel(config1);
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ManagedChannel channelb = manager.getChannel(config1);
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assertThat(channela).isSameInstanceAs(mockChannel1);
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assertThat(channelb).isSameInstanceAs(mockChannel1);
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verify(mockCreator, org.mockito.Mockito.times(1)).apply(config1);
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}
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@Test
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public void getChannel_differentConfig_shutsDownOldAndReturnsNew() {
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when(mockCreator.apply(config1)).thenReturn(mockChannel1);
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when(mockCreator.apply(config2)).thenReturn(mockChannel2);
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ManagedChannel channel1 = manager.getChannel(config1);
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assertThat(channel1).isSameInstanceAs(mockChannel1);
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ManagedChannel channel2 = manager.getChannel(config2);
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assertThat(channel2).isSameInstanceAs(mockChannel2);
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verify(mockChannel1).shutdown();
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verify(mockCreator, org.mockito.Mockito.times(1)).apply(config1);
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verify(mockCreator, org.mockito.Mockito.times(1)).apply(config2);
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}
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@Test
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public void close_shutsDownChannel() {
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when(mockCreator.apply(config1)).thenReturn(mockChannel1);
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manager.getChannel(config1);
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manager.close();
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verify(mockChannel1).shutdown();
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}
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}

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