Sending messages via WebSocketOutputStream is slow

[michbin]

Describe the bug
Sending messages through the WebSocketStreamHandler.WebSocketOutputStream is quite slow. This behavior is mainly caused by the flush() method. We often observed that flush() only returned after 100 ms which reduced the throughput significantly.

The root cause is the long wait time (100 ms!) in following code snippet:

      while (WebSocketStreamHandler.this.socket.queueSize() > 0) {
        try {
          Thread.sleep(100);
          ...

Client Version
19.0.1

Kubernetes Version
1.29

Java Version
Java 17

To Reproduce
Invoke Exec.exec(...) to create an ExecProcess.
Use the output stream returned by Process.getOutputStream().
Send data using write(...) calls and flush the stream afterwards.

Expected behavior
A wait time of 1 ms should be sufficient.

Server (please complete the following information):

• OS: Linux and Windows
• Environment: container and IDE

[brendandburns]

Happy to take PRs to improve this (for example making the wait configurable) or alternate mechanisms for ensuring the queue is flushed.