1) Generaly said Step Into works. It is tested. So, it should be some special
usecase.

2) Can you attach usecase for Java, if its repdoducible there?

Fixing this concrete exception is not a problem. But I am not sure if its cause
of your problem. Does this exception occures always?

If I remove java.lang from src.zip, and try to step into java.lang sources (in
J2SE project), debugger randomly seems to be confused - stepping and stopping in
sources which does not exist at all. Getting this exception:
Annotation: Exception occurred in Request Processor
com.sun.jdi.VMDisconnectedException: Socket closed
        at com.sun.tools.jdi.TargetVM.send(TargetVM.java:262)
        at
com.sun.tools.jdi.VirtualMachineImpl.sendToTarget(VirtualMachineImpl.java:879)
        at com.sun.tools.jdi.PacketStream.send(PacketStream.java:41)
        at
com.sun.tools.jdi.JDWP$ThreadReference$Status.enqueueCommand(JDWP.java:4126)
        at com.sun.tools.jdi.JDWP$ThreadReference$Status.process(JDWP.java:4112)
        at
com.sun.tools.jdi.ThreadReferenceImpl.jdwpStatus(ThreadReferenceImpl.java:184)
        at
com.sun.tools.jdi.ThreadReferenceImpl.isSuspended(ThreadReferenceImpl.java:200)
        at
org.netbeans.modules.debugger.jpda.JPDADebuggerImpl.run(JPDADebuggerImpl.java:884)
        at org.openide.util.Task.run(Task.java:189)
        at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:330)
[catch] at
org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:721)

I can show the difference between Beta and RC1

Are sources for your application enabled in sources view?

In both situation, it is able to step into and stop in non existing code.

What does it mean step into non existing code?

i.e :Thread main stopped at String.java:2236.
but all java.lang is not available, but debugger is still "somewhere". You
should press F7 couple times, to get cursor line visible again.

The same type of issue apparently breaks whole NB Mobility debugging. Debugger
step into source which does not exist a get completly confused

OK. What does it mean "completely confused"? I am simply still not able to
reproduce it. Can you create step by step "how to reproduce it" use case, plese?
Attach some project / sources here...

Thanks

Created attachment 21766 [details]
j2me project for reproduction

steps to reproduce in j2me project
-have mobility pack installed in netbeans
-unzip and open attached project in nb
-place breakpoint to line Display.getDisplay(this); in hanz/Midlet.java file
-Debug project
-wait when emulator will appeared and 'Launch' midlet
-it stops on breakpoint, do F7 - step into
*debuger goes to Object and get confused

OK. Thanks. Can you do the same excersize for J2SE usecase?

different output from beta and rc, 
--beta-------------------------------------
Attaching to localhost:4146
User program running
Breakpoint hit at line 19 in class hanz.Midlet by thread KVM_main.
Thread KVM_main stopped at Midlet.java:19.
User program running
Thread KVM_main stopped at Midlet.java:19.
User program running
Thread KVM_main stopped at Midlet.java:20.
User program running
--------------------------------------------
--rc----------------------------------------
Attaching to localhost:4295
User program running
Breakpoint hit at line 19 in class hanz.Midlet by thread KVM_main.
Thread KVM_main stopped at Midlet.java:19.
Thread KVM_main stopped at Display.java:558.
Thread KVM_main stopped at Display.java:558.
Thread KVM_main stopped at Midlet.java:19.
Thread KVM_main stopped at Object.java:356.
User program running
Thread KVM_main stopped at Object.java:356.
Thread KVM_main stopped at Object.java:356.
Thread KVM_main stopped at Object.java:356.

it steps into classes where it shouldn't. It's definitely regression from beta
where it worked perfectly.

It is apparently caused by fix for 56053. 

fixed in trunk:
Checking in src/org/netbeans/modules/debugger/jpda/JPDADebuggerImpl.java;
/cvs/debuggerjpda/src/org/netbeans/modules/debugger/jpda/JPDADebuggerImpl.java,v
 <--  JPDADebuggerImpl.java
new revision: 1.68; previous revision: 1.67
done
Checking in
src/org/netbeans/modules/debugger/jpda/actions/ContinueActionProvider.java;
/cvs/debuggerjpda/src/org/netbeans/modules/debugger/jpda/actions/ContinueActionProvider.java,v
 <--  ContinueActionProvider.java
new revision: 1.5; previous revision: 1.4
done
Checking in
src/org/netbeans/modules/debugger/jpda/actions/JPDADebuggerActionProvider.java;
/cvs/debuggerjpda/src/org/netbeans/modules/debugger/jpda/actions/JPDADebuggerActionProvider.java,v
 <--  JPDADebuggerActionProvider.java
new revision: 1.6; previous revision: 1.5
done
Checking in src/org/netbeans/modules/debugger/jpda/actions/PauseActionProvider.java;
/cvs/debuggerjpda/src/org/netbeans/modules/debugger/jpda/actions/PauseActionProvider.java,v
 <--  PauseActionProvider.java
new revision: 1.6; previous revision: 1.5
done
Checking in src/org/netbeans/modules/debugger/jpda/actions/StepActionProvider.java;
/cvs/debuggerjpda/src/org/netbeans/modules/debugger/jpda/actions/StepActionProvider.java,v
 <--  StepActionProvider.java
new revision: 1.14; previous revision: 1.13
done
Checking in
src/org/netbeans/modules/debugger/jpda/actions/StepIntoActionProvider.java;
/cvs/debuggerjpda/src/org/netbeans/modules/debugger/jpda/actions/StepIntoActionProvider.java,v
 <--  StepIntoActionProvider.java
new revision: 1.10; previous revision: 1.9
done

Diff to review:
Index: src/org/netbeans/modules/debugger/jpda/JPDADebuggerImpl.java
===================================================================
RCS file:
/cvs/debuggerjpda/src/org/netbeans/modules/debugger/jpda/JPDADebuggerImpl.java,v
retrieving revision 1.64.2.2
diff -r1.64.2.2 JPDADebuggerImpl.java
85d84
< import org.openide.util.RequestProcessor;
93c92
< public class JPDADebuggerImpl extends JPDADebugger implements Runnable {
---
> public class JPDADebuggerImpl extends JPDADebugger {
580d578
<         RequestProcessor.getDefault ().post (this, 200);
716a715
>             JPDAThreadImpl t = (JPDAThreadImpl) getCurrentThread ();
877,889d875
<     }
<     
<     public void run () {
<         if (getState () == JPDADebugger.STATE_DISCONNECTED)
<             return;
<         JPDAThreadImpl t = (JPDAThreadImpl) getCurrentThread ();
<         if (t != null) {
<             if ( t.getThreadReference ().isSuspended () &&
<                  getState () == STATE_RUNNING
<             )
<                 setState (STATE_STOPPED);
<         }
<         RequestProcessor.getDefault ().post (this, 200);
cvs server: Diffing src/org/netbeans/modules/debugger/jpda/actions
Index: src/org/netbeans/modules/debugger/jpda/actions/ContinueActionProvider.java
===================================================================
RCS file:
/cvs/debuggerjpda/src/org/netbeans/modules/debugger/jpda/actions/ContinueActionProvider.java,v
retrieving revision 1.3.38.1
diff -r1.3.38.1 ContinueActionProvider.java
21a22
> import java.util.Map;
41c42,45
<     public ContinueActionProvider (ContextProvider lookupProvider) {
---
>     private boolean j2meDebugger = false;
>     
>     
>     public ContinueActionProvider (ContextProvider contextProvider) {
43c47
<             (JPDADebuggerImpl) lookupProvider.lookupFirst 
---
>             (JPDADebuggerImpl) contextProvider.lookupFirst 
45a50,52
>         Map properties = (Map) contextProvider.lookupFirst (null, Map.class);
>         if (properties != null)
>             j2meDebugger = properties.containsKey ("J2ME_DEBUGGER");
57a65,71
>         if (j2meDebugger) {
>             setEnabled (
>                 ActionsManager.ACTION_CONTINUE,
>                 debuggerState == JPDADebugger.STATE_STOPPED
>             );
>             return;
>         }
Index:
src/org/netbeans/modules/debugger/jpda/actions/JPDADebuggerActionProvider.java
===================================================================
RCS file:
/cvs/debuggerjpda/src/org/netbeans/modules/debugger/jpda/actions/JPDADebuggerActionProvider.java,v
retrieving revision 1.4.4.1
diff -r1.4.4.1 JPDADebuggerActionProvider.java
15a16
> import com.sun.jdi.ThreadReference;
20a22
> import com.sun.jdi.request.StepRequest;
63,67c65,67
< 
<     /**
<     * Removes last step request.
<     */
<     void removeStepRequests () {
---
>     
>     void removeStepRequests (ThreadReference tr) {
>         //S ystem.out.println ("removeStepRequests");
73,76c73,81
<             if (verbose) {
<                 Iterator it = l.iterator ();
<                 while (it.hasNext ())
<                     System.out.println("  remove request " + it.next ());
---
>             Iterator it = l.iterator ();
>             while (it.hasNext ()) {
>                 StepRequest stepRequest = (StepRequest) it.next ();
>                 if (stepRequest.thread ().equals (tr)) {
>                     //S ystem.out.println("  remove request " + stepRequest);
>                     erm.deleteEventRequest (stepRequest);
>                     break;
>                 }
>                 //S ystem.out.println("  do not remove " + stepRequest + " : "
+ stepRequest.thread ());
78,79d82
<                 
<             erm.deleteEventRequests (l);
Index: src/org/netbeans/modules/debugger/jpda/actions/PauseActionProvider.java
===================================================================
RCS file:
/cvs/debuggerjpda/src/org/netbeans/modules/debugger/jpda/actions/PauseActionProvider.java,v
retrieving revision 1.3.38.1
diff -r1.3.38.1 PauseActionProvider.java
20a21
> import java.util.Map;
41c42,45
<     public PauseActionProvider (ContextProvider lookupProvider) {
---
>     private boolean j2meDebugger = false;
>     
>     
>     public PauseActionProvider (ContextProvider contextProvider) {
43c47
<             (JPDADebuggerImpl) lookupProvider.lookupFirst 
---
>             (JPDADebuggerImpl) contextProvider.lookupFirst 
45a50,52
>         Map properties = (Map) contextProvider.lookupFirst (null, Map.class);
>         if (properties != null)
>             j2meDebugger = properties.containsKey ("J2ME_DEBUGGER");
57a65,71
>         if (j2meDebugger) {
>             setEnabled (
>                 ActionsManager.ACTION_PAUSE,
>                 debuggerState == JPDADebugger.STATE_RUNNING
>             );
>             return;
>         }
Index: src/org/netbeans/modules/debugger/jpda/actions/StepActionProvider.java
===================================================================
RCS file:
/cvs/debuggerjpda/src/org/netbeans/modules/debugger/jpda/actions/StepActionProvider.java,v
retrieving revision 1.12.2.1
diff -r1.12.2.1 StepActionProvider.java
19a20
> import com.sun.jdi.VirtualMachine;
110,112d110
<             // 1) remove old request
<             removeStepRequests ();
<             
114c112,113
<                 // 2) init info about current state
---
>                 // 1) init info about current state & remove old
>                 //    requests in the current thread
116a116
>                 removeStepRequests (tr);
124c124,125
<                 // 3) create new step request
---
>                 
>                 // 2) create new step request
138c139
<                 // 4) resume JVM
---
>                 // 3) resume JVM
143c144
<             //S ystem.out.println("/nStepAction.do end");
---
>             //S ystem.out.println("/nStepAction.doAction end");
166a168
>             System.out.println("/nStepAction.exec");
169c171
<             removeStepRequests ();
---
>             removeStepRequests (((LocatableEvent) ev).thread ());
177c179,189
<             // 3) stop execution here?
---
>             // 3) ignore step events in not current threads
>             JPDAThreadImpl ct = (JPDAThreadImpl) getDebuggerImpl ().
>                 getCurrentThread ();
>             if (ct != null &&
>                 !ct.getThreadReference ().equals (tr)
>             ) {
>                 // step finished in different thread => ignore
>                 return true; // resume debugging
>             }
>             
>             // 4) stop execution here?
188a201
>                 System.out.println("/nStepAction.exec end - do not resume");
198a212
>             System.out.println("/nStepAction.exec end - resume");
200d213
< 
Index: src/org/netbeans/modules/debugger/jpda/actions/StepIntoActionProvider.java
===================================================================
RCS file:
/cvs/debuggerjpda/src/org/netbeans/modules/debugger/jpda/actions/StepIntoActionProvider.java,v
retrieving revision 1.9
diff -r1.9 StepIntoActionProvider.java
117c117,119
<                 removeStepRequests ();
---
>                 ThreadReference tr = ((JPDAThreadImpl) getDebuggerImpl ().
>                     getCurrentThread ()).getThreadReference ();
>                 removeStepRequests (tr);
135c137,139
<             removeStepRequests ();
---
>             ThreadReference tr = ((JPDAThreadImpl) getDebuggerImpl ().
>                 getCurrentThread ()).getThreadReference ();
>             removeStepRequests (tr);
160c164
<             removeStepRequests ();
---
>             removeStepRequests (le.thread ());
199,200c203,204
<     void removeStepRequests () {
<         super.removeStepRequests ();
---
>     void removeStepRequests (ThreadReference tr) {
>         super.removeStepRequests (tr);
207d210
<         removeStepRequests ();
209a213
>         removeStepRequests (tr);

I need QA review and Dev review here!

Created attachment 21893 [details]
Latest diff (together with 58348)

latest fix looks ok in rc41. It doesn't step into unexisting sources in j2me
projects. Marking as verified, set TM=4.1 when it's fixed in release41 branch,
thanks.

The diff (together with #58348) looks good to me. Reviewed.

Seems to be OK.

fixed in release41 branch:

Checking in viewmodel/src/org/netbeans/modules/viewmodel/TreeTable.java;
/cvs/debuggercore/viewmodel/src/org/netbeans/modules/viewmodel/TreeTable.java,v
 <--  TreeTable.java
new revision: 1.15.2.1; previous revision: 1.15
done
Checking in src/org/netbeans/modules/debugger/jpda/JPDADebuggerImpl.java;
/cvs/debuggerjpda/src/org/netbeans/modules/debugger/jpda/JPDADebuggerImpl.java,v
 <--  JPDADebuggerImpl.java
new revision: 1.64.2.3; previous revision: 1.64.2.2
done
Checking in
src/org/netbeans/modules/debugger/jpda/actions/ContinueActionProvider.java;
/cvs/debuggerjpda/src/org/netbeans/modules/debugger/jpda/actions/ContinueActionProvider.java,v
 <--  ContinueActionProvider.java
new revision: 1.3.38.2; previous revision: 1.3.38.1
done
Checking in src/org/netbeans/modules/debugger/jpda/actions/PauseActionProvider.java;
/cvs/debuggerjpda/src/org/netbeans/modules/debugger/jpda/actions/PauseActionProvider.java,v
 <--  PauseActionProvider.java
new revision: 1.3.38.2; previous revision: 1.3.38.1
done
Checking in src/org/netbeans/modules/debugger/jpda/expr/Evaluator.java;
/cvs/debuggerjpda/src/org/netbeans/modules/debugger/jpda/expr/Evaluator.java,v 
<--  Evaluator.java
new revision: 1.14.6.1; previous revision: 1.14
done