[resteasy-dev] RESTEasy asynchronous processing with @Suspended -- actually synchronous?

[Steven Schlansker]

Hi again,

I was somewhat disappointed to not get an answer here, but I did a fair amount more digging,
and managed to find Filter30Dispatcher (which just moved recently for upcoming 3.1.0)

Unfortunately then I found that the documentation does not mention this
class at all, but at least it exists!
(at least not on http://docs.jboss.org/resteasy/docs/3.0.19.Final/userguide/html_single/index.html )

So far it seems to work well.  Better than FilterDispatcher, at least :)
Let me know if there's any gotchas or other bits that I've missed.

Best,
Steven

> On Oct 7, 2016, at 1:21 PM, Steven Schlansker <sschlansker at opentable.com> wrote:
> 
> [ apologies for the rampant cross-posting, it looks like I might have been sending this to old mailing lists, and getting lost in the void? ]
> 
> Hello resteasy-dev,
> 
> I am trying to use the new JAX-RS 2.0 @Suspended AsyncResponse mechanism to write
> a service that expects many idling connections (awaiting an event via long-poll),
> and therefore seems like a good candidate for asynchronous responses, so as not
> to use a large number of waiting threads.
> 
> The resource code is very simple:
> 
>  @GET
>  @Produces(MediaType.APPLICATION_JSON)
>  public void watchForChanges(
>          @Suspended AsyncResponse asyncResponse,
>          @QueryParam("since") long since)
>  {
>      controller.watchForChanges(since, asyncResponse::resume);
>  }
> 
> The intent is that watchForChanges places the (inferred) Consumer<ResponseObject> on a queue,
> and returns immediately.  Later on a background thread comes by and completes the request.
> 
> However, when testing with say 20 clients, it sure looks like the end result is still a
> thread per request model:
> 
> 
> "qtp1718322084-43" - Thread t at 43
> java.lang.Thread.State: WAITING
> 	at sun.misc.Unsafe.park(Native Method)
> 	- parking to wait for <3537ebd5> (a java.util.concurrent.CountDownLatch$Sync)
> 	at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
> 	at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
> 	at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireSharedInterruptibly(AbstractQueuedSynchronizer.java:997)
> 	at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(AbstractQueuedSynchronizer.java:1304)
> 	at java.util.concurrent.CountDownLatch.await(CountDownLatch.java:231)
> 	at org.jboss.resteasy.core.SynchronousExecutionContext$SynchronousAsynchronousResponse.initialRequestThreadFinished(SynchronousExecutionContext.java:127)
> 	at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:411)
> 	at org.jboss.resteasy.core.SynchronousDispatcher.invokePropagateNotFound(SynchronousDispatcher.java:247)
> 	at org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:225)
> 	at org.jboss.resteasy.plugins.server.servlet.FilterDispatcher.doFilter(FilterDispatcher.java:62)
> 	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1676)
> <snip Jetty handler / filter chain>
> 	at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:319)
> 	at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:253)
> 	at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:273)
> 	at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:95)
> 	at org.eclipse.jetty.io.SelectChannelEndPoint$2.run(SelectChannelEndPoint.java:93)
> 	at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.executeProduceConsume(ExecuteProduceConsume.java:303)
> 	at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.produceConsume(ExecuteProduceConsume.java:148)
> 	at org.eclipse.jetty.util.thread.strategy.ExecuteProduceConsume.run(ExecuteProduceConsume.java:136)
> 	at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:671)
> 	at org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:589)
> 	at java.lang.Thread.run(Thread.java:745)
> 
> 
> 
> The concept of a "SynchronousAsynchronousResponse" and implementation of in particular SynchronousDispatcher#invoke seem to be totally not what I want:
>          /**
>           * Callback by the initial calling thread.  This callback will probably do nothing in an asynchronous environment
>           * but will be used to simulate AsynchronousResponse in vanilla Servlet containers that do not support
>           * asychronous HTTP.
>           *
>           */
>          request.getAsyncContext().getAsyncResponse().initialRequestThreadFinished();
> 
> 
> What am I doing wrong?  How do I get truly asynchronous processing?
> 
> This is with RESTEasy 3.0.18 running on Jetty 9.3.11
> 
> Thanks for any advice,
> Steven

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