nil-xit

A lightweight distributed reactive runtime for shared state synchronization, live instrumentation, and multi-client visualization.

Core idea

nil-xit separates execution, state, and frontend rendering.

The nil-xit runtime owns frame semantics, lifecycle, and message handling. Execution is expressed as frame logic; transport is delegated to nil-service.
Frontends are ephemeral sessions This enables live shared visualization of running systems, tests, and experiments without embedding a UI framework into the host application.

System model

frontend (projection layer)
- stateless
- emits signals
- renders values
nil-service (transport dependency)
- event loop
- message forwarding
- multiplexing clients
- no semantic awareness
nil-xit (runtime kernel)
- owns frames
- owns semantics
- owns handlers
- owns state model

Frames (primary runtime unit)

Frames are stateful runtime objects and the only distributed unit in nil-xit.

A Frame encapsulates:

Signals (event definitions)
Values (reactive state objects)

Frame primitives

Signals are internal event channels.

Values are externally accessible reactive state objects exposed via handles.

Runtime Flow

User constructs nil-service (transport backend)
User constructs nil-xit with nil-service injected
User defines Frames via nil-xit, including their signals and values
User starts nil-service event loop
One or more frontends connect and synchronize state
Signals flow into frames from frontends
Frame values are synchronized back to all frontends

Key properties

Backend is the single source of truth
State is automatically rehydrated on reconnect
UI frameworks are interchangeable

What you can build

🧪 Test instrumentation

Wrap test frameworks (e.g. gtest) so each test emits observable frames for live visualization.

📓 Notebook integration

Attach Jupyter notebooks to a running runtime and visualize state in real time.

📊 Multi-client dashboards

Multiple independent UIs can observe and interact with the same execution.

Supported languages

C / C++ (core)
Python bindings
Lua (experimental / internal)

Frontend is language-agnostic as long as it can communicate with nil-service.

Current reference frontend:

Svelte

Status

Actively used in internal systems
Pre-v1 API (subject to change)
Frontend ergonomics still evolving

Examples

nil-sandbox-py
- simple Python sandbox using nil-clix, nil-service and nil-xit
nil-xit-gtest (vcpkg)
- adapter layer of nil-xit to a testing framework
nil-xit-gtest (deb system isntall)
- adapter layer of nil-xit to a testing framework