Hi Marco,
We have BaseX 11.9 here with FAIRLOCK = false and PARALLEL=8 (wonder if this can be a hint).
I agree, your stack trace clearly indicates an issue with the disabled FAIRLOCK mode. In our productive code, we always use fair locking, and we are considering removing this mode in a future version, so it may well be that this option has been neglected over the years. Would you be able to use the default mode, or are there specific reasons why you have resorted to stricter locking? Ciao, Christian ________________________________ Von: Marco Lettere via BaseX-Talk <basex-talk@mailman.uni-konstanz.de> Gesendet: Montag, 16. März 2026 12:52 An: basex-talk@mailman.uni-konstanz.de <basex-talk@mailman.uni-konstanz.de> Betreff: [basex-talk] Deadlock on a subset of RestXQs Dear all, I'm currently running into an issue that makes my service stop serving a set of RESTXQ calls indefinitely without any clearly visible cause. When this happens an inspection of the threads returns that there are more than 100 threads locked with the stack trace reported in [1]. The architecture comprises a RestXQ service (without any DB) that receives a POST request, let's call it API. In the implementation of the request handling it "xquery:fork-joins" about 12 operations which mainly consist of http requests to another service or reading of local files, in order to cache (or refresh) information that is kept in a BaseX store locally. During the all of the said operation it also performs some write oprations (mainly to log the outcome of the operation) on a BaseX DB which runs on a different BaseX server (say Persistence) process through db:query(). We notice that many calls to the API continue to be served. Mainly calls that remain on the API itself or access other DBs on Persistence. Only all the calls that access the same store or persistence DB somehow stop being served. In the logs we see the request is received but it never either succeeds nor fails. We have BaseX 11.9 here with FAIRLOCK = false and PARALLEL=8 (wonder if this can be a hint). Because we are rather clueless I ask whether anyone has a hint about where we should restrict our investigations? Thank you very much! Marco. [1] "qtp192881625-748" #748 prio=5 os_prio=0 cpu=11.89ms elapsed=240.61s tid=0x00007abe1a7c4330 nid=0x289f6 in Object.wait() [0x00007abe1a4b2000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(java.base@17.0.12/Native<mailto:java.base@17.0.12/Native> Method) - waiting on <no object reference available> at java.lang.Object.wait(java.base@17.0.12/Object.java:338<mailto:java.base@17.0.12/Object.java:338>) at org.basex.core.locks.NonfairLockQueue.acquire(NonfairLockQueue.java:37) - locked <0x00000000802a93d8> (a org.basex.core.locks.NonfairLockQueue) at org.basex.core.locks.Locking.acquire(Locking.java:110) at org.basex.core.locks.Locking.acquire(Locking.java:89) at org.basex.core.jobs.Job.register(Job.java:48) at org.basex.http.restxq.RestXqResponse.serialize(RestXqResponse.java:81) at org.basex.http.web.WebResponse.create(WebResponse.java:58) at org.basex.http.restxq.RestXqServlet.run(RestXqServlet.java:70) at org.basex.http.BaseXServlet.service(BaseXServlet.java:68) at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:587) at org.eclipse.jetty.servlet.ServletHolder$NotAsync.service(ServletHolder.java:1410) at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:764) at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:529) at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:131) at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:598) at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:122) at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:223) at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:1580) at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:221) at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1381) at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:176) at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:484) at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:1553) at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:174) at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1303) at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:129) at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:122) at org.eclipse.jetty.server.handler.gzip.GzipHandler.handle(GzipHandler.java:822) at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:122) at org.eclipse.jetty.server.Server.handle(Server.java:563) at org.eclipse.jetty.server.HttpChannel$RequestDispatchable.dispatch(HttpChannel.java:1598) at org.eclipse.jetty.server.HttpChannel.dispatch(HttpChannel.java:753) at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:501) at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:287) at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:314) at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:100) at org.eclipse.jetty.io.SelectableChannelEndPoint$1.run(SelectableChannelEndPoint.java:53) at org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.runTask(AdaptiveExecutionStrategy.java:421) at org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.consumeTask(AdaptiveExecutionStrategy.java:390) at org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.tryProduce(AdaptiveExecutionStrategy.java:277) at org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.run(AdaptiveExecutionStrategy.java:199) at org.eclipse.jetty.util.thread.ReservedThreadExecutor$ReservedThread.run(ReservedThreadExecutor.java:411) at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:969) at org.eclipse.jetty.util.thread.QueuedThreadPool$Runner.doRunJob(QueuedThreadPool.java:1194) at org.eclipse.jetty.util.thread.QueuedThreadPool$Runner.run(QueuedThreadPool.java:1149) at java.lang.Thread.run(java.base@17.0.12/Thread.java:840<mailto:java.base@17.0.12/Thread.java:840>)