Add virtual thread attribute to WsWebSocketContainer

[adj5672]

In my app, I use WsWebSocketContainer to create websocket client.
As the number of sessions increases, memory usage also increased. So "OOM Killed" occured frequently.
I know that It is a normal situation in thread-per-connection model which is current applied.
Current model have advantage that It is very intuitive and sometimes it behaves like kind of rate limiter.

But I think that threads for R/W may not working busy in some case.
Also platform thread will be created twice of session count and it allocate a lot of default stack memory.
furthermore context switching cost expensive too when using platform thread.

So I think that instead of create two platform thread per session, using virtual thread will be helpful in some cases.
Since I may not understand overall about websocket codes and architecture, I just create draft pull request.
Adding choice to use virtual threads would be helpful for optimizing memory usage.

[VolareYang]

Hi! I have a question: how do I enable virtual threads in Tomcat 11? After enabling virtual threads, which log in Tomcat's startup logs can I check to confirm that virtual threads are actually being used?

My environment:
Tomcat: 11.0.23
JDK: 21
server.xml configuration:

Startup logs show:
23-Jun-2026 14:51:39.306 INFO [main] org.apache.coyote.AbstractProtocol.start Starting ProtocolHandler ["http-nio-8080"]
23-Jun-2026 14:51:39.313 INFO [main] org.apache.catalina.startup.Catalina.start Server startup in [799] milliseconds

When I check the thread stack with the jstack command, I don't see any threads related to tomcat-virt- so I can't be sure if virtual threads are actually enabled. Could you guide me? Thanks!