Ytukyg

What could cause this to happen? My web application has frozen up and stopped responding. I went and did a thread dump and found several threads all BLOCKED inside Thymeleaf:

Thread 3247: (state = BLOCKED)

 - sun.misc.Unsafe.park(boolean, long) @bci=0 (Compiled frame; information may be imprecise)

 - java.util.concurrent.locks.LockSupport.park(java.lang.Object) @bci=14, line=175 (Compiled frame)

 - java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt() @bci=1, line=836 (Interpreted frame)

 - java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireSharedInterruptibly(int) @bci=72, line=997 (Interpreted frame)

 - java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(int) @bci=24, line=1304 (Compiled frame)

 - java.util.concurrent.Semaphore.acquire() @bci=5, line=312 (Compiled frame)

 - org.thymeleaf.util.ResourcePool.allocate() @bci=4, line=108 (Compiled frame)

 - org.thymeleaf.templateparser.xmlsax.AbstractNonValidatingSAXTemplateParser.parseTemplateUsingPool(org.thymeleaf.Configuration, java.lang.String, java.io.Reader, org.thymeleaf.util.ResourcePool) @bci=2, line=124 (Compiled frame)

 - org.thymeleaf.templateparser.xmlsax.AbstractNonValidatingSAXTemplateParser.parseTemplate(org.thymeleaf.Configuration, java.lang.String, java.io.Reader) @bci=8, line=116 (Compiled frame)

 - org.thymeleaf.TemplateRepository.getTemplate(org.thymeleaf.TemplateProcessingParameters) @bci=556, line=278 (Compiled frame)

 - org.thymeleaf.TemplateEngine.process(org.thymeleaf.TemplateProcessingParameters, org.thymeleaf.fragment.IFragmentSpec, java.io.Writer) @bci=11, line=1104 (Compiled frame)

 - org.thymeleaf.TemplateEngine.process(java.lang.String, org.thymeleaf.context.IProcessingContext, org.thymeleaf.fragment.IFragmentSpec, java.io.Writer) @bci=110, line=1060 (Compiled frame)

 - org.thymeleaf.TemplateEngine.process(java.lang.String, org.thymeleaf.context.IContext, org.thymeleaf.fragment.IFragmentSpec, java.io.Writer) @bci=17, line=1011 (Compiled frame)

 - org.thymeleaf.spring4.view.ThymeleafView.renderFragment(org.thymeleaf.fragment.IFragmentSpec, java.util.Map, javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse) @bci=590, line=335 (Compiled frame)

 - org.thymeleaf.spring4.view.ThymeleafView.render(java.util.Map, javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse) @bci=5, line=190 (Compiled frame)

What could cause this? The presentation-layer code has not changed with the last release of the application. The application is fairly mature and stable. I'm not sure where to start investigating. Application is redeployed back to previous release for now while I try to reproduce the issue through a load-test.

Why would Thymeleaf require any kind of locking? There seems to be some fundamental architectural aspect of Thymeleaf at play here, that I don't understand.

This may not be technically a "deadlock" by the most strict definitions, but the result is the same.

The answer, it turns out, is that running out of heap space can cause the above contention.

Further investigation (we didn't have to look very far) revealed that the JVM was running out of heap space due to some overzealous caching in a related application that shares the same JVM.