[CAMEL-11731] Servlet Component isn't really async

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.18.4, 2.19.2
• Fix Version/s: 3.7.0
• Component/s: camel-servlet

Environment

All

• Estimated Complexity: Moderate
• Assignee: Unassigned
• Reporter: Nick Houghton
• Created: 01/Sep/17 01:34
• Updated: 20/Nov/20 09:08
• Resolved: 20/Nov/20 09:08

Description

So my assumption reading the servlet component doco is that with 2.18+ and a Servlet 3+ container, the component supports async, which it kind of does with the async=true init config, and there is even a method in CamelServlet called "doServiceAsync" but from what i can tell it doesn't really do it in a asynchronous manner, where there are no blocked threads while a request is awaiting an async operation (like an AHC call for example).

Looking at:
https://github.com/apache/camel/blob/master/components/camel-http-common/src/main/java/org/apache/camel/http/common/CamelServlet.java

While processing a request, we check if we are in async mode and call doServiceAsync..

 @Override
    protected final void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        if (isAsync()) {
            final AsyncContext context = req.startAsync();
            //run async
            context.start(() -> doServiceAsync(context));
        } else {
            doService(req, resp);
        }
    }

then in doServiceAsync() we call doService().. and then we call getProcessor().process(exchange), not process(exchange, asyncCallback) which is the proper async method..

try {
            if (log.isTraceEnabled()) {
                log.trace("Processing request for exchangeId: {}", exchange.getExchangeId());
            }
            // process the exchange
            consumer.getProcessor().process(exchange);
        } catch (Exception e) {
            exchange.setException(e);
        }

So the actual behaviour is an inbound request in async mode that ends up just blocking waiting for the request to complete, in a totally sync manner. I presume this is not the desired behaviour?

It seems the fix would be to move the doService() logic to doServiceAsync() and have doService() call it and use the AsyncProcessorConverterHelper. Or the other alternative would be to update the documentation to explicitly note that it is actually not async at all.

I can probably PR it in, just wanted to get thoughts on the actual intention.

Issue Links

• links to: GitHub Pull Request #2188
• links to: GitHub Pull Request #2188
• links to: GitHub Pull Request #4617