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

[Steven Schlansker]

Hello resteasy users,

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)

   Locked ownable synchronizers:
	- None

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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