macOS: JDTLS java process shows “Not Responding” in Activity Monitor

Environment

• macOS version: 26.1
• Extension: Language Support for Java(TM) by Red Hat version: 1.50.0
• JDK used by JDTLS (java -version and/or ps command line): 21.0.9-macosx-aarch64
• ps -ef output

  502 17937 17590   0  6:19PM ??         7:25.31 /Users/<user>/.cursor/extensions/redhat.java-1.50.0-darwin-arm64/jre/21.0.9-macosx-aarch64/bin/java --add-modules=ALL-SYSTEM --add-opens java.base/java.util=ALL-UNNAMED --add-opens java.base/java.lang=ALL-UNNAMED --add-opens java.base/sun.nio.fs=ALL-UNNAMED -Declipse.application=org.eclipse.jdt.ls.core.id1 -Dosgi.bundles.defaultStartLevel=4 -Declipse.product=org.eclipse.jdt.ls.core.product -Djava.import.generatesMetadataFilesAtProjectRoot=false -DDetectVMInstallationsJob.disabled=true -Dfile.encoding=utf8 -XX:+UseParallelGC -XX:GCTimeRatio=4 -XX:AdaptiveSizePolicyWeight=90 -Dsun.zip.disableMemoryMapping=true -Xmx2G -Xms100m -Xlog:disable -javaagent:/Users/<user>/.cursor/extensions/redhat.java-1.50.0-darwin-arm64/lombok/lombok-1.18.39-4050.jar -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/Users/<user>/Library/Application Support/Cursor/User/workspaceStorage/b073665c2bc84ec3e79c32587934d14c/redhat.java -Daether.dependencyCollector.impl=bf -jar /Users/<user>/.cursor/extensions/redhat.java-1.50.0-darwin-arm64/server/plugins/org.eclipse.equinox.launcher_1.7.100.v20251111-0406.jar -configuration /Users/<user>/Library/Application Support/Cursor/User/globalStorage/redhat.java/1.50.0/config_mac -data /Users/<user>/Library/Application Support/Cursor/User/workspaceStorage/b073665c2bc84ec3e79c32587934d14c/redhat.java/jdt_ws --pipe=/private/var/folders/cp/bcjqx5q56h7gp_3kts42xglm0000gp/T/lsp-aa7656daf3ce78c3a57214fd2e50ecf6.sock

Repro / When it happens

• Project type: Maven/Gradle
• Steps leading to hang:
• Does it recover on its own? No

Observed

• Activity Monitor shows java (Not Responding) PID 17937 with low CPU

Attachments

• threadump of java process 17937.vscode-java-plugin.txt
• Cursor Output (Java) logs + Extension Host logs

Dec 24, 2025 6:19:17 PM org.apache.aries.spifly.BaseActivator log
INFO: Registered provider ch.qos.logback.classic.spi.LogbackServiceProvider of service org.slf4j.spi.SLF4JServiceProvider in bundle ch.qos.logback.classic
Dec 24, 2025 6:28:44 PM com.microsoft.java.debug.plugin.internal.JavaDebuggerServerPlugin start
INFO: Starting com.microsoft.java.debug.plugin
Dec 24, 2025 6:31:26 PM org.eclipse.lsp4j.jsonrpc.RemoteEndpoint handleCancellation
WARNING: Unmatched cancel notification for request id 214
Dec 24, 2025 6:36:01 PM org.eclipse.lsp4j.jsonrpc.RemoteEndpoint handleCancellation
WARNING: Unmatched cancel notification for request id 977
Dec 24, 2025 6:46:24 PM org.eclipse.lsp4j.jsonrpc.RemoteEndpoint handleCancellation
WARNING: Unmatched cancel notification for request id 2084
Dec 24, 2025 6:47:47 PM org.eclipse.lsp4j.jsonrpc.RemoteEndpoint handleCancellation
WARNING: Unmatched cancel notification for request id 2432
Dec 24, 2025 6:52:33 PM org.eclipse.lsp4j.jsonrpc.RemoteEndpoint handleCancellation
WARNING: Unmatched cancel notification for request id 2883
Dec 24, 2025 8:28:39 PM org.eclipse.lsp4j.jsonrpc.RemoteEndpoint handleCancellation
WARNING: Unmatched cancel notification for request id 4289
Dec 24, 2025 8:28:39 PM org.eclipse.lsp4j.jsonrpc.RemoteEndpoint handleCancellation
WARNING: Unmatched cancel notification for request id 4286
Dec 24, 2025 8:28:39 PM org.eclipse.lsp4j.jsonrpc.RemoteEndpoint handleCancellation
WARNING: Unmatched cancel notification for request id 4293
Dec 25, 2025 10:32:20 AM org.eclipse.lsp4j.jsonrpc.RemoteEndpoint handleCancellation
WARNING: Unmatched cancel notification for request id 5863
Dec 25, 2025 10:42:54 AM org.eclipse.lsp4j.jsonrpc.RemoteEndpoint handleCancellation
WARNING: Unmatched cancel notification for request id 6305
Dec 25, 2025 10:42:54 AM org.eclipse.lsp4j.jsonrpc.RemoteEndpoint handleCancellation
WARNING: Unmatched cancel notification for request id 6307
Dec 25, 2025 10:42:54 AM org.eclipse.lsp4j.jsonrpc.RemoteEndpoint handleCancellation
WARNING: Unmatched cancel notification for request id 6308
Dec 25, 2025 10:42:54 AM org.eclipse.lsp4j.jsonrpc.RemoteEndpoint handleCancellation
WARNING: Unmatched cancel notification for request id 6309
Dec 25, 2025 10:42:54 AM org.eclipse.lsp4j.jsonrpc.RemoteEndpoint handleCancellation
WARNING: Unmatched cancel notification for request id 6310

Start with the attached thread dump for PID 17937 and the Cursor Java and Extension Host logs, then inspect how JDTLS is launched on macOS with the reported Java 21 configuration. Reproduce the non-responding state if possible; done means the cause is identified and the JDTLS process no longer hangs under the reported conditions.