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https://issues.apache.org/jira/browse/CAMEL-11731?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16348320#comment-16348320
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ASF GitHub Bot commented on CAMEL-11731:
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onderson commented on issue #2188: CAMEL-11731 - add asynccallback and sync
camel and servlet async APIs
URL: https://github.com/apache/camel/pull/2188#issuecomment-362216834
AFAIK, async servlet API handles requests by writing to HttpServletResponse
and setting context.complete(). Currently (before what i have done) what is
done in CamelServlet is to do this and process camel's exchange with
`consumer.getProcessor().process`. What i have added is to call
`consumer.getAsyncProcessor().process(exchange, asyncCallback)` with a proper
asyncCallBack in which callkback.done(false) is called after completing to
write to HttpServletResponse, which will trigger context.complete().
If you can describe what your thinking around the subject of the complexity,
i'd like to try to implement..
Thanks for the review.
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> Servlet Component isn't really async
> ------------------------------------
>
> Key: CAMEL-11731
> URL: https://issues.apache.org/jira/browse/CAMEL-11731
> Project: Camel
> Issue Type: Improvement
> Components: camel-servlet
> Affects Versions: 2.18.4, 2.19.2
> Environment: All
> Reporter: Nick Houghton
> Assignee: Önder Sezgin
> Priority: Major
> Fix For: Future
>
>
> 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..
> {code:java}
> @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);
> }
> }
> {code}
> then in doServiceAsync() we call doService().. and then we call
> getProcessor().process(exchange), not process(exchange, asyncCallback) which
> is the proper async method..
> {code:java}
> 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);
> }
> {code}
> 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.
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