Avoid the issue of connections not being released.

When channelizer.supportsIdleMonitor is false, enable TCP Keep-Alive
to avoid the issue of connections not being released.

Enable TCP Keep-Alive to detect if the remote peer is still reachable.
Keep-Alive sends periodic probes to check if the remote peer is still active.
If the remote peer is unreachable, the connection will be closed, preventing resource leaks and avoiding the maintenance of stale connections.

gremlin-server/src/main/java/org/apache/tinkerpop/gremlin/server/GremlinServer.java

@@ -161,6 +161,14 @@ public synchronized CompletableFuture<ServerGremlinExecutor> start() throws Exce
 
             channelizer = createChannelizer(settings);
             channelizer.init(serverGremlinExecutor);
+            // When the channelizer does not support idle monitoring, enable the ChannelOption.SO_KEEPALIVE feature.
+            if (!channelizer.supportsIdleMonitor()) {
+                // Enable TCP Keep-Alive to detect if the remote peer is still reachable.
+                // Keep-Alive sends periodic probes to check if the remote peer is still active.
+                // If the remote peer is unreachable, the connection will be closed, preventing resource leaks and
+                // avoiding the maintenance of stale connections.
+                b.childOption(ChannelOption.SO_KEEPALIVE, true);
+            }
             b.group(bossGroup, workerGroup)
                     .childHandler(channelizer);
             if (isEpollEnabled){