Reduce WebSocket flush wait from 100ms to 1ms

[Copilot]

The WebSocketOutputStream.flush() method was blocking for 100ms per iteration while waiting for the queue to drain, creating a throughput bottleneck for streaming operations like Exec.exec().

Changes

• Reduced sleep interval from 100ms to 1ms in flush loop
• Added constants FLUSH_WAIT_MILLIS (1ms) and MAX_FLUSH_ITERATIONS (10000) to replace magic numbers
• Maintained 10-second total timeout (10000 iterations × 1ms)

Before:

Thread.sleep(100);  // Wait 100ms per iteration
if (i++ > 100) {    // 100 iterations = 10s timeout

After:

Thread.sleep(FLUSH_WAIT_MILLIS);      // Wait 1ms per iteration
if (i++ > MAX_FLUSH_ITERATIONS) {     // 10000 iterations = 10s timeout

This provides up to 100× faster flush behavior while preserving the same maximum wait time.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Sending messages via WebSocketOutputStream is slow</issue_title>
<issue_description>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
  </issue_description>

<agent_instructions>Please evaluate if this is still an issue and shorten the wait time to 1ms</agent_instructions>

Comments on the Issue (you are @copilot in this section)

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

• Fixes Sending messages via WebSocketOutputStream is slow #4000

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