Are virtual threads supported?

[celtric]

I'm using resteasy-core version 6.2.10.Final (latest one right now), together with Jetty 12.0.12 on Java 21.

I think I'm observing virtual thread pinning the carrier thread without any synchronized lock in our logic:

#70 "" virtual
      java.base/jdk.internal.misc.Unsafe.park(Native Method)
      java.base/java.lang.VirtualThread.parkOnCarrierThread(VirtualThread.java:661)
      java.base/java.lang.VirtualThread.park(VirtualThread.java:593)
      java.base/java.lang.System$2.parkVirtualThread(System.java:2643)
      java.base/jdk.internal.misc.VirtualThreads.park(VirtualThreads.java:54)
      java.base/java.util.concurrent.locks.LockSupport.park(LockSupport.java:219)
      java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:754)
      java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:990)
      java.base/java.util.concurrent.locks.ReentrantLock$Sync.lock(ReentrantLock.java:153)
      java.base/java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:322)
      *********(HealthCheckServlet.java:45)
      java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
      java.base/java.lang.reflect.Method.invoke(Method.java:580)
      org.jboss.resteasy.core.MethodInjectorImpl.invoke(MethodInjectorImpl.java:154)
      org.jboss.resteasy.core.MethodInjectorImpl.invoke(MethodInjectorImpl.java:118)
      org.jboss.resteasy.core.ResourceMethodInvoker.internalInvokeOnTarget(ResourceMethodInvoker.java:560)
      org.jboss.resteasy.core.ResourceMethodInvoker.invokeOnTargetAfterFilter(ResourceMethodInvoker.java:452)
      org.jboss.resteasy.core.ResourceMethodInvoker.lambda$invokeOnTarget$2(ResourceMethodInvoker.java:413)
      org.jboss.resteasy.core.interception.jaxrs.PreMatchContainerRequestContext.filter(PreMatchContainerRequestContext.java:321)
      org.jboss.resteasy.core.ResourceMethodInvoker.invokeOnTarget(ResourceMethodInvoker.java:415)
      org.jboss.resteasy.core.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:378)
      org.jboss.resteasy.core.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:356)
      org.jboss.resteasy.core.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:70)
      org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:429)
      org.jboss.resteasy.core.SynchronousDispatcher.lambda$invokePropagateNotFound$6(SynchronousDispatcher.java:275)
      org.jboss.resteasy.core.SynchronousDispatcher.lambda$preprocess$0(SynchronousDispatcher.java:154)
      org.jboss.resteasy.core.interception.jaxrs.PreMatchContainerRequestContext.filter(PreMatchContainerRequestContext.java:321)
      org.jboss.resteasy.core.SynchronousDispatcher.preprocess(SynchronousDispatcher.java:157)
      org.jboss.resteasy.core.SynchronousDispatcher.invokePropagateNotFound(SynchronousDispatcher.java:260)
      org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:224)
      org.jboss.resteasy.plugins.server.servlet.FilterDispatcher.doFilter(FilterDispatcher.java:62)
      com.google.inject.servlet.FilterChainInvocation.doFilter(FilterChainInvocation.java:82)
      ...

Which leads me to this particular method:

https://github.com/resteasy/resteasy/blob/main/resteasy-core/src/main/java/org/jboss/resteasy/core/interception/jaxrs/PreMatchContainerRequestContext.java#L275

public synchronized BuiltResponse filter() {

My understanding is that this synchronized block negates the yielding of the virtual thread and effectively pins the carrier, negating all the benefits of going with virtual threads (and with severe degradation in our particular case, as the virtual thread scheduler pool is much smaller by default than the thread pool used by default by Jetty).

I see that the latest release 7.0.0.Alpha3 still contains the same synchronized block, so I may be mislead in my findings. Could you confirm if virtual threads are supported?

Thanks

[jamezp]

There is a plan to look at this, but we've not yet done it. It's going to be quite a large undertaking. It's something I'd like to get done though and will make it a higher priority. There are several places where synchronized is used so it's going to take some time and thought about how other clients might be using it.

I've created https://issues.redhat.com/browse/RESTEASY-3540 to track this.

[celtric]

Thanks @jamezp for the context and quick answer

[stevenschlansker]

The JDK is also working to remove the problem with synchronized pinning virtual threads:
https://bugs.openjdk.org/browse/JDK-8337395