Make NettyStreamFactoryFactory implement AutoCloseable

driver-core/src/main/com/mongodb/connection/NettyTransportSettings.java

@@ -87,8 +87,7 @@ public Builder socketChannelClass(final Class<? extends SocketChannel> socketCha
         /**
          * Sets the event loop group.
          *
-         * <p>It is highly recommended to supply your own event loop group and manage its shutdown.  Otherwise, the event
-         * loop group created by default will not be shutdown properly.</p>
+         * <p>The application is responsible for shutting down the provided {@code eventLoopGroup}</p>
          *
          * @param eventLoopGroup the event loop group that all channels created by this factory will be a part of
          * @return this

driver-core/src/main/com/mongodb/internal/connection/AsynchronousSocketChannelStreamFactoryFactory.java

@@ -36,4 +36,8 @@ public AsynchronousSocketChannelStreamFactoryFactory(final InetAddressResolver i
     public StreamFactory create(final SocketSettings socketSettings, final SslSettings sslSettings) {
         return new AsynchronousSocketChannelStreamFactory(inetAddressResolver, socketSettings, sslSettings);
     }
+
+    @Override
+    public void close() {
+    }
 }

driver-core/src/main/com/mongodb/internal/connection/StreamFactoryFactory.java

@@ -22,7 +22,7 @@
 /**
  * A factory of {@code StreamFactory} instances.
  */
-public interface StreamFactoryFactory {
+public interface StreamFactoryFactory extends AutoCloseable {
 
     /**
      * Create a {@code StreamFactory} with the given settings.
@@ -32,4 +32,7 @@ public interface StreamFactoryFactory {
      * @return a stream factory that will apply the given settins
      */
     StreamFactory create(SocketSettings socketSettings, SslSettings sslSettings);
+
+    @Override
+    void close();
 }

driver-core/src/main/com/mongodb/internal/connection/TlsChannelStreamFactoryFactory.java

@@ -59,7 +59,7 @@
 /**
  * A {@code StreamFactoryFactory} that supports TLS/SSL.  The implementation supports asynchronous usage.
  */
-public class TlsChannelStreamFactoryFactory implements StreamFactoryFactory, Closeable {
+public class TlsChannelStreamFactoryFactory implements StreamFactoryFactory {
 
     private static final Logger LOGGER = Loggers.getLogger("connection.tls");
 

driver-core/src/main/com/mongodb/internal/connection/netty/NettyStreamFactoryFactory.java

@@ -47,6 +47,7 @@
 public final class NettyStreamFactoryFactory implements StreamFactoryFactory {
 
     private final EventLoopGroup eventLoopGroup;
+    private final boolean ownsEventLoopGroup;
     private final Class<? extends SocketChannel> socketChannelClass;
     private final ByteBufAllocator allocator;
     @Nullable
@@ -202,6 +203,15 @@ public StreamFactory create(final SocketSettings socketSettings, final SslSettin
                 sslContext);
     }
 
+    @Override
+    public void close() {
+         if (ownsEventLoopGroup) {
+             // ignore the returned Future.  This is in line with MongoClient behavior to not block waiting for connections to be returned
+             // to the pool
+             eventLoopGroup.shutdownGracefully();
+         }
+    }
+
     @Override
     public boolean equals(final Object o) {
         if (this == o) {
@@ -225,6 +235,7 @@ private NettyStreamFactoryFactory(final Builder builder) {
         allocator = builder.allocator == null ? ByteBufAllocator.DEFAULT : builder.allocator;
         socketChannelClass = builder.socketChannelClass == null ? NioSocketChannel.class : builder.socketChannelClass;
         eventLoopGroup = builder.eventLoopGroup == null ? new NioEventLoopGroup() : builder.eventLoopGroup;
+        ownsEventLoopGroup = builder.eventLoopGroup == null;
         sslContext = builder.sslContext;
         inetAddressResolver = builder.inetAddressResolver;
     }

driver-reactive-streams/src/main/com/mongodb/reactivestreams/client/MongoClients.java

@@ -127,10 +127,9 @@ public static MongoClient create(final MongoClientSettings settings, @Nullable f
         }
         StreamFactory streamFactory = getStreamFactory(streamFactoryFactory, settings, false);
         StreamFactory heartbeatStreamFactory = getStreamFactory(streamFactoryFactory, settings, true);
-        AutoCloseable externalResourceCloser = streamFactoryFactory instanceof AutoCloseable ? (AutoCloseable) streamFactoryFactory : null;
         MongoDriverInformation wrappedMongoDriverInformation = wrapMongoDriverInformation(mongoDriverInformation);
         Cluster cluster = createCluster(settings, wrappedMongoDriverInformation, streamFactory, heartbeatStreamFactory);
-        return new MongoClientImpl(settings, wrappedMongoDriverInformation, cluster, externalResourceCloser);
+        return new MongoClientImpl(settings, wrappedMongoDriverInformation, cluster, streamFactoryFactory);
     }
 
     /**