fix: disable lockedSynchronizers in dumpAllThreads to avoid safepoint heap scan (#16194)

`ThreadMXBean.dumpAllThreads(true, true)` with lockedSynchronizers=true
forces the JVM to scan the entire heap at a safepoint to find all
AbstractOwnableSynchronizer instances. On ZGC with large heaps (65GB+),
this causes ~37-second safepoint pauses that freeze all application
threads, leading to cascading thread pool exhaustion.

Change lockedSynchronizers from true to false. This retains locked
monitor information (derived from thread stacks, cheap) but skips the
expensive heap scan. Only java.util.concurrent.locks ownership info
is lost from the thread dump output.

Fixes #16194

Author: eddieran

dubbo-common/src/main/java/org/apache/dubbo/common/utils/JVMUtil.java

@@ -33,7 +33,12 @@
 public class JVMUtil {
     public static void jstack(OutputStream stream) throws Exception {
         ThreadMXBean threadMxBean = ManagementFactory.getThreadMXBean();
-        for (ThreadInfo threadInfo : threadMxBean.dumpAllThreads(true, true)) {
+        // Pass lockedSynchronizers=false to avoid a full heap scan at safepoint.
+        // With lockedSynchronizers=true, the JVM iterates the entire heap to find all
+        // AbstractOwnableSynchronizer instances. On ZGC with large heaps, this causes
+        // tens-of-seconds safepoint pauses due to load barrier overhead on every reference.
+        // See: https://github.com/apache/dubbo/issues/16194
+        for (ThreadInfo threadInfo : threadMxBean.dumpAllThreads(true, false)) {
             stream.write(getThreadDumpString(threadInfo).getBytes(StandardCharsets.UTF_8));
         }
     }