Document vtable (Virtual Method Table) - Value 5

[LSantha]

vtable (Virtual Method Table)

Document the vtable JNode concept in the wiki.

Value: 5

Concept Summary

Method dispatch table for virtual method calls in class hierarchy. vtable enables efficient virtual method dispatch by providing an index-based lookup table for method implementations in the class hierarchy.

Key Files

• core/src/core/org/jnode/vm/classmgr/vtable.java
• core/src/core/org/jnode/vm/classmgr/VirtualMethods.java

Occurrences

~180 references in virtual methods package

Wiki Status

NOT documented

Bridges

Virtual methods, JIT compiler, Method dispatch

Instructions

Skill to Use

Use the [[update-wiki|update-wiki skill]] (load with skill({ name: "update-wiki" })) for understanding JNode internals.

Context Research

Review vtable.java and VirtualMethods.java to understand the virtual method table. Study how vtable is constructed for each class, how method indices are assigned, and how virtual calls are resolved. Research how vtable interacts with JIT compilation.

Update index.md

• Pages table: Add entry for vtable.md
• Concepts → Pages table: Add "vtable" mapping to [[vtable]]
• Source Path → Pages table: Add mappings for core/src/core/org/jnode/vm/classmgr/vtable.java
• Task Routing table: Add relevant task route(s)

Task Routing Suggestions

1. Virtual method debugging: vtable is central to virtual dispatch
2. JIT optimization: Understanding vtable is key for JIT decisions
3. Inheritance issues: vtable structure affects inheritance behavior

Wiki Page Structure

# vtable (Virtual Method Table)

> Method dispatch table for virtual method calls in class hierarchy.

## Overview
2-3 paragraph explanation of vtable, its role in virtual method dispatch, and how it enables efficient method calls.

## Key Components
| Class / File | Role |
|---|---|
| `core/src/core/org/jnode/vm/classmgr/vtable.java` | vtable implementation |
| `core/src/core/org/jnode/vm/classmgr/VirtualMethods.java` | Virtual methods support |

## How It Works
Explanation of how vtable works, how it's constructed for each class, how method indices are assigned, and how virtual calls use vtable.

## Gotchas & Non-Obvious Behavior
- vtable must be carefully maintained during inheritance
- Method overrides affect vtable layout
- JIT can optimize vtable access

## Related Pages
- [[Virtual-Methods]]
- [[IMT]]
- [[CompiledIMT]]

---

Related Concepts: Virtual methods, Method dispatch, vtable, Inheritance, JIT

[LSantha]

/oc Please proceed with this task.

[LSantha]

/oc Please proceed with this task.

[LSantha]

/oc Please proceed with this task.

[opencode-agent]

vtable wiki page created and pushed.

• .wiki/vtable.md — dedicated vtable deep-dive covering TIB slot assignment, TIBBuilder construction, override vs. append rules, synthetic abstract method cloning, and JIT resolution
• .wiki/index.md — updated all four tables (Pages, Concepts→Pages, Source Path→Pages, Task Routing)
• .wiki/Glossary.md — vtable entry now links to [[vtable]]
• .wiki/Changelog.md — new entry added
• .wiki/Virtual-Methods.md — cross-linked to [[vtable]]
• Issue Document vtable (Virtual Method Table) - Value 5 #84 closed

https://github.com/LSantha/jnode_ai/wiki/vtable

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[opencode-agent]

Wiki: Add vtable spoke page

Task completed. The vtable wiki page was created and pushed successfully.

Created: .wiki/vtable.md (139 lines)
Updated: index.md (Pages, Concepts → Pages, Source Path → Pages, Task Routing tables), Glossary.md (vtable entry), Changelog.md

The page documents:

• TIB structure (vtable starts at index 5 via FIRST_METHOD_INDEX)
• TIBBuilder construction (inherit from superclass, override/replace, append new methods)
• nameSignature2Index HashMap for O(1) method lookup
• JIT codegen for invokevirtual using direct TIB access
• Gotchas (visibility-based slot reuse for package-private overrides, abstract method cloning, JIT index stability)

Wiki URL: https://github.com/LSantha/jnode_ai/wiki/vtable

Issue: #84 already closed.

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