Hello! I am working on a new kind of debugger which extracts information about the state of Java programs through the JDI to build RDF knowledge graphs.
While working on the project, I noticed that there is certain information about the program state that is accessible through JDWP, but which is hidden by the
JDI interfaces (see below for examples).I am curious, whether this was done to simplify the interface, or if there is
a deeper reason behind this, e.g. because the information in question is unreliable etc. If there is no such reason, I might try to modify the JDI reference implementation to provide this information to me. *First Example: Retrieving Objects by ID*The ObjectReference JDI interface does allow to retrieve the unique id assigned to
an object by the JDWP agent.However, it seems it is not possible to construct an ObjectReference from such
an id. That is, one can not quickly look up an object by its id, but has to search through all objects to find it again.Looking at the JDWP specification, it seems that the underlying JDWP protocol
does support looking up objects using just their id: https://docs.oracle.com/en/java/javase/17/docs/specs/jdwp/jdwp-protocol.html#JDWP_ObjectReferenceThe reference implementation of the `ObjectReference` interface also seems to
only require this id to retrieve all required information: https://github.com/openjdk/jdk/blob/dfacda488bfbe2e11e8d607a6d08527710286982/src/jdk.jdi/share/classes/com/sun/tools/jdi/ObjectReferenceImpl.java#L109 /My question now is:/Is there a specific reason that there is no public factory method to construct
an ObjectReference from an object id?Or would it be "safe" to create a custom `ObjectReference` implementation that allows this, as long as it deals with the `INVALID_OBJECT` error case of JDWP?
*Second Example: Variable Locations*The JDWP `VariableTable` command reply does contain the code index of variables. Nevertheless, it is neither possible to retrieve the code index of a variable through the `LocalVariable` JDI interface, nor through the `Method` interface.
Meanwhile, internally, the `LocalVariable` reference implementation does seem
to store the scope of a variable: https://github.com/openjdk/jdk/blob/dfacda488bfbe2e11e8d607a6d08527710286982/src/jdk.jdi/share/classes/com/sun/tools/jdi/LocalVariableImpl.java#L56 The Eclipse JDI implementation also stores the plain code index value: https://git.eclipse.org/c/jdt/eclipse.jdt.debug.git/tree/org.eclipse.jdt.debug/jdi/org/eclipse/jdi/internal/LocalVariableImpl.java#n63Is there a specific reason, why this location information is not exposed in the
public interface? Thank you very much for reading my questions. Can you help me to answer them? Best regards, Anton Haubner
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