Hello,
I am observing an issue with virtual threads in Undertow in Spring Boot v3.3.0-M2. When using spring.threads.virtual.enabled=true in the application.properties or
@Bean
public UndertowDeploymentInfoCustomizer undertowDeploymentInfoCustomizer() {
return deploymentInfo -> deploymentInfo.setExecutor(Executors.newVirtualThreadPerTaskExecutor());
}
as a configuration, the memory usage of the application increases dramatically under load. I performed a wrk test with the command wrk -d30 -t10 -c150 http://localhost:8080 and my application's memory usage increased to 20GB in just 30 seconds.
Interestingly, when using a profiler, I observed that the JVM reported significantly lower memory usage than what the activity monitor was showing.
The application eventually crashes with an OOM error:
2024-02-29T19:08:44.404-08:00 ERROR 91152 --- [ndertow-1044448] io.undertow.request : UT005023: Exception handling request to /
jakarta.servlet.ServletException: Handler dispatch failed: java.lang.OutOfMemoryError: Cannot reserve 16364 bytes of direct buffer memory (allocated: 17179860008, limit: 17179869184)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1104) ~[spring-webmvc-6.1.4.jar:6.1.4]
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:979) ~[spring-webmvc-6.1.4.jar:6.1.4]
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1014) ~[spring-webmvc-6.1.4.jar:6.1.4]
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:903) ~[spring-webmvc-6.1.4.jar:6.1.4]
at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:527) ~[jakarta.servlet-api-6.0.0.jar:6.0.0]
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:885) ~[spring-webmvc-6.1.4.jar:6.1.4]
at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:614) ~[jakarta.servlet-api-6.0.0.jar:6.0.0]
at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:74) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:129) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at com.example.demo.RequestFilter.doFilter(RequestFilter.java:19) ~[main/:na]
at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:67) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-6.1.4.jar:6.1.4]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.1.4.jar:6.1.4]
at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:67) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-6.1.4.jar:6.1.4]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.1.4.jar:6.1.4]
at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:67) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-6.1.4.jar:6.1.4]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.1.4.jar:6.1.4]
at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:67) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.servlet.handlers.FilterHandler.handleRequest(FilterHandler.java:84) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.servlet.handlers.ServletChain$1.handleRequest(ServletChain.java:68) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.servlet.handlers.RedirectDirHandler.handleRequest(RedirectDirHandler.java:68) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:117) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) ~[undertow-core-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46) ~[undertow-core-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:60) ~[undertow-core-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:77) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.security.handlers.AbstractSecurityContextAssociationHandler.handleRequest(AbstractSecurityContextAssociationHandler.java:43) ~[undertow-core-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) ~[undertow-core-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.servlet.handlers.SendErrorPageHandler.handleRequest(SendErrorPageHandler.java:52) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) ~[undertow-core-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:276) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:135) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:132) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.servlet.core.ServletRequestContextThreadSetupAction$1.call(ServletRequestContextThreadSetupAction.java:48) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.servlet.core.ContextClassLoaderSetupAction$1.call(ContextClassLoaderSetupAction.java:43) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:256) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:101) ~[undertow-servlet-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.server.Connectors.executeRootHandler(Connectors.java:393) ~[undertow-core-2.3.12.Final.jar:2.3.12.Final]
at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:859) ~[undertow-core-2.3.12.Final.jar:2.3.12.Final]
at java.base/java.lang.VirtualThread.run(VirtualThread.java:309) ~[na:na]
Output of java -version
openjdk version "21.0.2" 2024-01-16
OpenJDK Runtime Environment GraalVM CE 21.0.2+13.1 (build 21.0.2+13-jvmci-23.1-b30)
OpenJDK 64-Bit Server VM GraalVM CE 21.0.2+13.1 (build 21.0.2+13-jvmci-23.1-b30, mixed mode, sharing)
I was able to reproduce this behavior when running the application in a Docker container, when compiling to a native-image, on different JDKs (OpenJDK, GraalVM, and Corretto), and on different macOS architectures (Intel and Apple silicon). Tagging related issue https://github.com/spring-projects/spring-boot/issues/38819.
Thank you.
Comment From: mhalbritter
That's one of the drawbacks when moving from a thread pool to virtual threads per task without a pool. When using thread pools, they usually have an upper bound for the size, limiting the maximum resource consumption. Unpooled virtual threads don't have that. I assume the application you're benchmarking is a simple demo application which just returns some hardcoded data? Because usually, if there's no pool in the webserver, some other pool in the application is limiting the throughput (e.g. the connection pool to the database).
Btw, you don't see the memory usage in VisualVM, as this is direct allocated memory, which is off-heap.
Comment From: Tythor
Yes, it's the Spring Boot demo project with a basic GET endpoint with no return value. Sorry, could you explain the cause for this again? Aren't virtual threads still limited by the size of the platform threads in the carrier pool? The Tomcat and Jetty servlets don't seem to have the same issue when using virtual threads. Also, thank you for the explanation about the profiler.
Comment From: mhalbritter
One possibility could be this:
1. VT1: Start accepting the request
2. VT1: Allocate memory
3. VT1: Block on something (maybe reading http from the TCP socket)
4. VT1: Handle request
5. VT1: Free memory
With enough requests lined up, the block at 3. could be the reason why the memory is exhausted. At this block, the scheduler frees the underlying platform thread, and switches to a new virtual thread, which allocates memory, blocks, a new virtual thread is scheduled, allocates memory, etc etc.
Comment From: mhalbritter
You could use a SimpleAsyncTaskExecutor with setConcurrencyLimit to limit the maximum allowed number of virtual threads.
Comment From: MetaiR
as long as I remember, there is an issue that talks about virtual threads in Spring Boot here: https://github.com/spring-projects/spring-boot/issues/38819
there is one part I saw that says in version 3.3.x the usage of the virtual thread must automatically happen for undertow. so can it be related to this issue?
can u check if this also happens with version 3.2.x ? @Tythor
Comment From: Tythor
@MetaiR
Yes, I can confirm the same behavior happens in v3.2.3. Since spring.threads.virtual.enabled=true does not apply to Undertow servlets until v3.3.0, I had to use the undertowDeploymentInfoCustomizer to enable virtual threading.
@mhalbritter
I attempted to use a SimpleAsyncTaskExecutor with virtual threads with a concurrency limit of 10, but the issue still persisted.
@Bean
public UndertowDeploymentInfoCustomizer undertowDeploymentInfoCustomizer() {
return deploymentInfo -> {
SimpleAsyncTaskExecutor simpleAsyncTaskExecutor = new SimpleAsyncTaskExecutor();
simpleAsyncTaskExecutor.setVirtualThreads(true);
simpleAsyncTaskExecutor.setConcurrencyLimit(10);
deploymentInfo.setExecutor(simpleAsyncTaskExecutor);
};
}
However, this led me to try using a non virtual threaded executor instead. Surprisingly, I observed the same behavior, albeit at a much slower growth rate of about 2m for 20GB instead of 30s. These three executors produced similar results:
deploymentInfo.setExecutor(new SimpleAsyncTaskExecutor());
deploymentInfo.setExecutor(Executors.newThreadPerTaskExecutor(Thread.ofPlatform().factory()));
deploymentInfo.setExecutor(Executors.newThreadPerTaskExecutor(Executors.defaultThreadFactory()));
However, when using
deploymentInfo.setExecutor(Executors.newCachedThreadPool());
the memory growth disappeared. Looking into the implementation, the main difference is that the cachedThreadPool executor has a keepAliveTime of 60s, while the others have a keepAliveTime of 0s.
Reducing the keepAliveTime to as low as 1s did not cause the memory growth in my tests. But setting it to 0s reproduced the same issue.
deploymentInfo.setExecutor(new ThreadPoolExecutor(0, Integer.MAX_VALUE, 1L, TimeUnit.SECONDS, new SynchronousQueue<>()));
So it looks like this issue is not unique to virtual threads, but perhaps with the way Undertow is handling executors?
Comment From: mhalbritter
Yeah, looks like something is wrong here, but it doesn't seem to be in Spring Boot. Please open an issue on the Undertow tracker, and feel free to drop the link in this issue. Thanks!
Comment From: mhalbritter
We decided to reopen the issue. The out of box experience with virtual threads in undertow is bad, and if we (or the undertow team) can't fix the problems with it, we might remove virtual threads support for undertow again.
Comment From: Tythor
Okay, I was about to suggest disabling the auto configuration for spring.threads.virtual.enabled=true in v3.3.x. This issue would likely be a problem that most users will not be aware of. Thanks!
https://github.com/spring-projects/spring-boot/commit/cff1b33f8e30492aea5a14ab959752e96b7c3e16
Comment From: mhalbritter
Yeah, we shouldn't fiddle with the Undertow executors.
The default one produces this plot:
As soon as we meddle with it, it starts breaking.
With virtual threads:
With virtual threads and concurrency throttle to 200:
With platform threads and concurrency throttle to 200:
It breaks in all configurations when setting the executor.
I'm going to revert the virtual thread support for Undertow.
Comment From: wilkinsona
It looks like Undertow may have a memory leak. @Tythor, can you please retry your scenario with Undertow downgraded to 2.3.10.Final and see if it helps?
Comment From: Tythor
Hi @wilkinsona, downgrading Undertow to 2.3.10.Final on Spring Boot v3.3.0-M2 did significantly slow the memory growth. However, I am still seeing suspicious behavior when providing an executor in the UndertowDeploymentInfoCustomizer. Although I'm not sure if it's due to a memory leak or just inefficient memory consumption within Undertow. Perhaps @mhalbritter may be able to diagnose the issue better with his plots. I also tried using 2.3.11.Final and encountered the same issue as the one in 2.3.12.Final.
Comment From: mhalbritter
Undertow 2.3.10.Final, SimpleAsyncTaskExecutor with 200 concurrency limit and virtual threads enabled:
It's better, but there's still a problem somewhere.
Comment From: mhalbritter
This is what 2.3.10 with the default executor looks like:
Comment From: Tythor
Thank you @mhalbritter, these plots are very similar to the results I observed as well.
Comment From: mhalbritter
Btw, the tool I used is https://github.com/astrofrog/psrecord.
Comment From: cassiusvm
Hello,
I am using Spring Boot 3.2.4 and Undertow with OpenJDK by Corretto, I don't have this issue.
My application is an API REST, it is running by several days.
Comment From: wilkinsona
@cassiusvm How have you configured Undertow to use virtual threads?
Comment From: cassiusvm
@wilkinsona Right, using the @Configuration tip in a Docker image jelastic maven 3.9.5 OpenJDK 21.
My bad, I said Correto.
Comment From: time4tea
I realise its not a spring issue per-se, but hoping that this is useful.
When configuring with
Xnio.getInstance().setExternalExecutorService(Executors.newVirtualThreadPerTaskExecutor())
The service will quickly blow up.. I think due to use of ThreadLocal buffer strategy.
In DefaultByteBufferPool, the following line might cause a problem with virtual threads:
ThreadLocalData get() {
return localsByThread.get(Thread.currentThread());
}
It is possible to make it used unpooled buffers, with
io.undertow.Undertow.builder().setByteBufferPool(XnioByteBufferPool(Pool.DIRECT))
but the performance of this is worse (by 50%) than the default, so no point.
Anyhow, hope thats of some use if somebody is looking into this.
Comment From: JavaLionLi
Comment From: philwebb
Thanks @JavaLionLi. I'll update #38819 with that info.
Comment From: IgnacioPuigMargalef
Any updated info about last untertow version?
Comment From: mhalbritter
@IgnacioPuigMargalef About what exactly? We have added virtual thread support for Undertow with https://github.com/spring-projects/spring-boot/issues/38819.
Comment From: AkashB23
Is anybody else still facing the issue with the latest version of Undertow?
Seems like I tend to encounter the same behavior of memory leak even with latest undertow version and virtual thread configuration as suggested in this thread.
The RSS memory keeps ramping up along with the request count and never released back until the pod is killed to consume all native memory [configured to use directByteBuffer]
Tried to get details of any possible memory leak with JMELLOC but no luck there, the memory map also highlights the initial allocation of 200MB of directByteBuffer pool
Just disabling the virtual thread will resolve the issue, not able to find the exact cause
Undertow version: 2.3.17.Final and spring-boot-starter-undertow:jar:3.2.12
Comment From: mhalbritter
Have you tried with the latest Spring Boot version (3.4.1) which uses Undertow 2.3.18.Final?