`NoSuchElementException` from `ServiceLoader` in Async Context

[alexstewartja]

This report details a critical runtime exception encountered for derivatives trading (USDS Futures) within a Play Framework 3 / Pekko environment.

When initializing the WebSocket client within a CompletableFuture (e.g., on Play's default ForkJoinPool), the ServiceLoader mechanism fails to find Jetty WebSocket extension implementations.

• Error: java.util.NoSuchElementException originating from java.util.ServiceLoader and traced up through org.eclipse.jetty.websocket.api.ExtensionConfig.getParser.
• Cause: The ServiceLoader relies on the Thread.currentThread().getContextClassLoader(). When the initialization code runs on a worker thread from a thread pool (like ForkJoinPool), this context classloader may not have visibility of the full application dependency classpath where the Jetty service implementations reside.
• Trigger: Instantiating new DerivativesTradingUsdsFuturesWebSocketStreams(wsConnectionPool) inside a CompletableFuture.supplyAsync() block.

[alexstewartja]

This issue can be patched by wrapping the initialization call in a helper that temporarily sets the thread's context classloader to the main application classloader. This is a common pattern in environments with complex classloading like Play Framework.

Workaround for Play Framework:

public static <T> T withPlayClassLoader(Callable<T> block) throws Exception {
    ClassLoader playAppClassLoader = play.Application.class.getClassLoader();
    ClassLoader originalContextClassLoader = Thread.currentThread().getContextClassLoader();
    try {
        Thread.currentThread().setContextClassLoader(playAppClassLoader);
        return block.call();
    } finally {
        Thread.currentThread().setContextClassLoader(originalContextClassLoader);
    }
}

// Usage:
wsStreams = withPlayClassLoader(
    () -> new DerivativesTradingUsdsFuturesWebSocketStreams(clientConfiguration)
);

[theo-s68]

Hello @alexstewartja ,

Thanks for the report and for the documented solution as well.

Is there anything we could do on the SDK side to make it easier to use with Play framework ?

Thanks.