gcore a java process (in my case from cacao)

di64-x4450a-prg06<root># file /core.5692
/core.5692: ELF 32-bit LSB core file 80386 Version 1, from 'java'
di64-x4450a-prg06<root># /usr/jdk/instances/jdk1.6.0/bin/jstack -m /usr/jdk/instances/jdk1.6.0/bin/java /core.5692
Attaching to core /core.5692 from executable /usr/jdk/instances/jdk1.6.0/bin/java, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 10.0-b23
^Cjava.lang.RuntimeException: VM.initialize() was not yet called
        at sun.jvm.hotspot.runtime.VM.getVM(VM.java:359)
        at sun.jvm.hotspot.code.CodeCache.findBlob(CodeCache.java:79)
        at sun.jvm.hotspot.runtime.Frame.isCompiledFrame(Frame.java:141)
        at sun.jvm.hotspot.runtime.Frame.isJavaFrame(Frame.java:121)
        at sun.jvm.hotspot.runtime.Frame.isFirstFrame(Frame.java:164)
        at sun.jvm.hotspot.runtime.VFrame.sender(VFrame.java:116)
        at sun.jvm.hotspot.runtime.VFrame.javaSender(VFrame.java:151)
        at sun.jvm.hotspot.tools.PStack.initJFrameCache(PStack.java:208)
        at sun.jvm.hotspot.tools.PStack.run(PStack.java:66)
        at sun.jvm.hotspot.tools.PStack.run(PStack.java:53)
        at sun.jvm.hotspot.tools.PStack.run(PStack.java:48)
        at sun.jvm.hotspot.tools.JStack.run(JStack.java:60)
        at sun.jvm.hotspot.tools.Tool.start(Tool.java:221)
        at sun.jvm.hotspot.tools.JStack.main(JStack.java:86)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at sun.tools.jstack.JStack.runJStackTool(JStack.java:118)
        at sun.tools.jstack.JStack.main(JStack.java:84)
Exception in thread "main" java.lang.reflect.InvocationTargetException
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at sun.tools.jstack.JStack.runJStackTool(JStack.java:118)
        at sun.tools.jstack.JStack.main(JStack.java:84)
Caused by: java.lang.RuntimeException: VM.initialize() was not yet called
        at sun.jvm.hotspot.runtime.VM.getVM(VM.java:359)
        at sun.jvm.hotspot.runtime.solaris_x86.SolarisX86JavaThreadPDAccess.getThreadProxy(SolarisX86JavaThreadPDAccess.java:136)
        at sun.jvm.hotspot.runtime.JavaThread.getThreadProxy(JavaThread.java:272)
        at sun.jvm.hotspot.tools.PStack.initJFrameCache(PStack.java:218)
        at sun.jvm.hotspot.tools.PStack.run(PStack.java:66)
        at sun.jvm.hotspot.tools.PStack.run(PStack.java:53)
        at sun.jvm.hotspot.tools.PStack.run(PStack.java:48)
        at sun.jvm.hotspot.tools.JStack.run(JStack.java:60)
        at sun.jvm.hotspot.tools.Tool.start(Tool.java:221)
        at sun.jvm.hotspot.tools.JStack.main(JStack.java:86)
        ... 6 more


as you noticed I had to break the jstack using CTRL+C since it was just "stuck"

BUT
if I do :

di64-x4450a-prg06<root># /usr/jdk/instances/jdk1.6.0/bin/jsadebugd /usr/jdk/instances/jdk1.6.0/bin/java /core.5692
Attaching to core /core.5692 from executable /usr/jdk/instances/jdk1.6.0/bin/java and starting RMI services, please wait...
Debugger attached and RMI services started.
^Z
[1]+ Stopped /usr/jdk/instances/jdk1.6.0/bin/jsadebugd /usr/jdk/instances/jdk1.6.0/bin/java /core.5692
di64-x4450a-prg06<root># bg
[1]+ /usr/jdk/instances/jdk1.6.0/bin/jsadebugd /usr/jdk/instances/jdk1.6.0/bin/java /core.5692 &

di64-x4450a-prg06<root># /usr/jdk/instances/jdk1.6.0/bin/jstack localhost
Attaching to remote server localhost, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 10.0-b23
Deadlock Detection:

No deadlocks found.

Thread t@ 1616: (state = BLOCKED)
 - sun.misc.Unsafe.park(boolean, long) @bci=0 (Interpreted frame)
 - java.util.concurrent.locks.LockSupport.parkNanos(java.lang.Object, long) @bci=20, line=198 (Compiled frame)
 - java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(long) @bci=68, line=1963 (Compiled frame)
 - java.util.concurrent.LinkedBlockingQueue.poll(long, java.util.concurrent.TimeUnit) @bci=93, line=395 (Interpreted frame)
 - java.util.concurrent.ThreadPoolExecutor.getTask() @bci=62, line=944 (Interpreted frame)
 - java.util.concurrent.ThreadPoolExecutor$Worker.run() @bci=18, line=906 (Interpreted frame)
 - java.lang.Thread.run() @bci=11, line=619 (Interpreted frame)


Thread t@ 1615: (state = BLOCKED)
 - sun.misc.Unsafe.park(boolean, long) @bci=0 (Interpreted frame)
 - java.util.concurrent.locks.LockSupport.parkNanos(java.lang.Object, long) @bci=20, line=198 (Compiled frame)
 - java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(long) @bci=68, line=1963 (Compiled frame)
 - java.util.concurrent.LinkedBlockingQueue.poll(long, java.util.concurrent.TimeUnit) @bci=93, line=395 (Interpreted frame)
 - java.util.concurrent.ThreadPoolExecutor.getTask() @bci=62, line=944 (Interpreted frame)
 - java.util.concurrent.ThreadPoolExecutor$Worker.run() @bci=18, line=906 (Interpreted frame)
 - java.lang.Thread.run() @bci=11, line=619 (Interpreted frame)

.....

THEN jstack get's a bit further, BUT eventually gets stuck again:

Thread t@ 13: (state = BLOCKED)
 - java.lang.Object.wait(long) @bci=0 (Interpreted frame)
 - java.lang.ref.ReferenceQueue.remove(long) @bci=44, line=116 (Compiled frame)
 - java.lang.ref.ReferenceQueue.remove() @bci=2, line=132 (Compiled frame)
 - java.lang.ref.Finalizer$FinalizerThread.run() @bci=3, line=159 (Compiled frame)


^CError occurred during stack walking:
java.lang.RuntimeException: VM.initialize() was not yet called
        at sun.jvm.hotspot.runtime.VM.getVM(VM.java:359)
        at sun.jvm.hotspot.code.CodeCache.findBlob(CodeCache.java:79)
        at sun.jvm.hotspot.runtime.x86.X86Frame.adjustForDeopt(X86Frame.java:102)
        at sun.jvm.hotspot.runtime.x86.X86Frame.<init>(X86Frame.java:124)
        at sun.jvm.hotspot.runtime.x86.X86Frame.senderForCompiledFrame(X86Frame.java:373)
        at sun.jvm.hotspot.runtime.x86.X86Frame.sender(X86Frame.java:283)
        at sun.jvm.hotspot.runtime.Frame.sender(Frame.java:194)
        at sun.jvm.hotspot.runtime.Frame.realSender(Frame.java:199)
        at sun.jvm.hotspot.runtime.VFrame.sender(VFrame.java:119)
        at sun.jvm.hotspot.runtime.VFrame.javaSender(VFrame.java:151)
        at sun.jvm.hotspot.tools.StackTrace.run(StackTrace.java:76)
        at sun.jvm.hotspot.tools.StackTrace.run(StackTrace.java:45)
        at sun.jvm.hotspot.tools.JStack.run(JStack.java:60)
        at sun.jvm.hotspot.tools.Tool.start(Tool.java:221)
        at sun.jvm.hotspot.tools.JStack.main(JStack.java:86)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at sun.tools.jstack.JStack.runJStackTool(JStack.java:118)
        at sun.tools.jstack.JStack.main(JStack.java:84)

Exception in thread "main" java.lang.reflect.InvocationTargetException
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at sun.tools.jstack.JStack.runJStackTool(JStack.java:118)
        at sun.tools.jstack.JStack.main(JStack.java:84)
Caused by: java.lang.RuntimeException: VM.initialize() was not yet called
        at sun.jvm.hotspot.runtime.VM.getVM(VM.java:359)
        at sun.jvm.hotspot.runtime.JavaThread.next(JavaThread.java:114)
        at sun.jvm.hotspot.tools.StackTrace.run(StackTrace.java:65)
        at sun.jvm.hotspot.tools.StackTrace.run(StackTrace.java:45)
        at sun.jvm.hotspot.tools.JStack.run(JStack.java:60)
        at sun.jvm.hotspot.tools.Tool.start(Tool.java:221)
        at sun.jvm.hotspot.tools.JStack.main(JStack.java:86)
        ... 6 more

note that I pressed CTRL+C again

if needed I can get you access to a machine for troubleshooting
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