c-two 0.4.0

C-Two is a resource-RPC framework that enables resource-oriented classes to be remotely invoked across different processes or machines.

C-Two

A resource-oriented RPC framework for Python — turn stateful classes into location-transparent distributed resources.

中文版

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Basic Idea

• Resources, not services — C-Two doesn't expose RPC endpoints. It makes Python classes remotely accessible while preserving their stateful, object-oriented nature.

• Zero-copy when local, transparent when remote — Same-process calls skip serialization entirely. Cross-process calls use shared memory. Cross-machine calls go over HTTP. Your code doesn't change.

• Built for scientific Python — Native support for Apache Arrow, NumPy arrays, and large payloads (chunked streaming for data beyond 256 MB). Designed for computational workloads, not microservices.

• Rust-powered transport — The IPC layer uses a Rust buddy allocator for shared memory and a Rust HTTP relay for high-throughput networking.

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Quick Start

pip install c-two

Define a resource interface and its implementation

import c_two as cc

# Interface — declares which methods are remotely accessible
@cc.icrm(namespace='demo.counter', version='0.1.0')
class ICounter:
    def increment(self, amount: int) -> int: ...

    @cc.read
    def value(self) -> int: ...

    def reset(self) -> int: ...


# Implementation — a plain Python class holding state
class Counter:
    def __init__(self, initial: int = 0):
        self._value = initial

    def increment(self, amount: int) -> int:
        self._value += amount
        return self._value

    def value(self) -> int:
        return self._value

    def reset(self) -> int:
        old = self._value
        self._value = 0
        return old

Use it locally (zero serialization)

cc.register(ICounter, Counter(initial=100), name='counter')
counter = cc.connect(ICounter, name='counter')

counter.increment(10)    # → 110
counter.value()          # → 110
counter.reset()          # → 110 (returns old value)
counter.value()          # → 0

cc.close(counter)

Or remotely — same API, different address

# Server process
cc.set_address('ipc:///tmp/my_server')
cc.register(ICounter, Counter(), name='counter')

# Client process (separate terminal)
counter = cc.connect(ICounter, name='counter', address='ipc:///tmp/my_server')
counter.increment(5)     # works identically
cc.close(counter)

See examples/ for complete runnable demos.

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Core Concepts

ICRM — Interface

An ICRM (Interface of Core Resource Model) declares which CRM methods are remotely accessible. Decorated with @cc.icrm(), method bodies are ... (pure interface — no implementation).

@cc.icrm(namespace='demo.greeter', version='0.1.0')
class IGreeter:
    @cc.read                              # concurrent reads allowed
    def greet(self, name: str) -> str: ...

    @cc.read
    def language(self) -> str: ...

Methods can be annotated with @cc.read (concurrent access allowed) or left as default write (exclusive access).

CRM — Core Resource Model

A CRM is a plain Python class that holds state and implements domain logic. It is not decorated — the framework discovers its methods through the ICRM interface.

class Greeter:
    def __init__(self, lang: str = 'en'):
        self._lang = lang
        self._templates = {'en': 'Hello, {}!', 'zh': '你好, {}!'}

    def greet(self, name: str) -> str:
        return self._templates.get(self._lang, 'Hi, {}!').format(name)

    def language(self) -> str:
        return self._lang

Component — Consumer

Components consume CRM resources through ICRM proxies. The proxy is location-transparent — it works the same whether the CRM is in the same process or on a remote machine.

greeter = cc.connect(IGreeter, name='greeter')
greeter.greet('World')     # → 'Hello, World!'
cc.close(greeter)

@transferable — Custom Serialization

For custom data types that need to cross the wire, use @cc.transferable. Without it, pickle is used as fallback.

@cc.transferable
class GridAttribute:
    level: int
    global_id: int
    elevation: float

    def serialize(data: 'GridAttribute') -> bytes:
        # Custom serialization (e.g., Apache Arrow)
        ...

    def deserialize(raw: bytes) -> 'GridAttribute':
        ...

serialize and deserialize are written as instance-style methods but are automatically converted to @staticmethod by the framework.

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Examples

Single Process — Thread Preference

When cc.connect() targets a CRM registered in the same process, the proxy calls methods directly with zero serialization overhead.

import c_two as cc

# Register two CRMs in the same process
cc.register(IGreeter, Greeter(lang='en'), name='greeter')
cc.register(ICounter, Counter(initial=100), name='counter')

# Connect — zero-serde thread-local proxies
greeter = cc.connect(IGreeter, name='greeter')
counter = cc.connect(ICounter, name='counter')

print(greeter.greet('World'))    # → Hello, World!
print(counter.value())           # → 100
counter.increment(10)

# Cleanup
cc.close(greeter)
cc.close(counter)
cc.shutdown()

Best for: local prototyping, testing, single-machine computation.

Multi-Process — IPC

Separate server and client processes communicating over Unix domain sockets with shared memory.

Server (server.py):

import c_two as cc

cc.set_address('ipc://my_server')
cc.register(IGrid, grid_instance, name='grid')
print(f'Listening at {cc.server_address()}')

cc.serve()  # blocks until interrupted

Client (client.py):

import c_two as cc

grid = cc.connect(IGrid, name='grid', address='ipc://my_server')
infos = grid.get_grid_infos(1, [0, 1, 2])
keys = grid.subdivide_grids([1], [0])

cc.close(grid)
cc.shutdown()

Best for: multi-process on same host, worker isolation, high-throughput local IPC.

Cross-Machine — HTTP Relay

An HTTP relay bridges network requests to CRM processes running on IPC.

CRM Server (resource.py):

import c_two as cc

cc.set_address('ipc://grid_server')
cc.register(IGrid, grid_instance, name='grid')
# Auto-registers with relay when C2_RELAY_ADDRESS is set
cc.serve()

Relay (relay.py):

from c_two.transport.relay import Relay

relay = Relay(bind='127.0.0.1:8080')
relay.start(blocking=True)

Client (client.py):

import c_two as cc

# Same API — just change the address
grid = cc.connect(IGrid, name='grid', address='http://127.0.0.1:8080')
grid.get_grid_infos(1, [0])

cc.close(grid)

Best for: network-accessible services, web integration, cross-machine deployment.

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Architecture

The design philosophy of C-Two is not to define services, but to empower resources.

In scientific computation, resources encapsulating complex state and domain-specific operations need to be organized into cohesive units. We call these Core Resource Models (CRMs). Applications care more about how to interact with resources than where they are located. We call resource consumers Components. C-Two provides location transparency and uniform resource access, allowing components to interact with CRMs as if they were local objects.

graph LR
    subgraph Component Layer
        C1[Component] -->|cc.connect| P1[ICRM Proxy]
        C2[Component] -->|cc.connect| P2[ICRM Proxy]
    end

    subgraph Transport Layer
        P1 --> T{Protocol<br/>Auto-detect}
        P2 --> T
        T -->|thread://| TH[Thread<br/>Direct Call]
        T -->|ipc://| IPC[IPC<br/>UDS + SHM]
        T -->|http://| HTTP[HTTP<br/>Relay]
    end

    subgraph CRM Layer
        TH --> CRM1[CRM Instance]
        IPC --> CRM1
        HTTP --> CRM1
    end

Component Layer

Client-side consumers that access remote resources through ICRM proxies. The proxy provides full type safety and location transparency — components don't know (or care) where the CRM is running.

• Script-based: cc.connect(ICRMClass, name='...', address='...') returns a typed ICRM proxy
• Function-based: @cc.runtime.connect decorator injects the ICRM proxy as the first parameter

CRM Layer

Server-side stateful resources exposed through standardized ICRM interfaces.

• CRM: Plain Python class — state + domain logic. Not decorated.
• ICRM: Interface class decorated with @cc.icrm(). Only methods declared here are remotely accessible.
• @transferable: Custom serialization for domain data types (e.g., Apache Arrow for scientific data).
• @cc.read / @cc.write: Concurrency annotations — parallel reads, exclusive writes.

Transport Layer

Protocol-agnostic communication with automatic protocol detection based on address scheme:

Scheme	Transport	Use case
thread://	In-process direct call	Zero serialization, testing
ipc:///path	Unix domain socket + shared memory	Multi-process, same host
http://host:port	HTTP relay	Cross-machine, web-compatible

The IPC transport uses a control-plane / data-plane separation: method routing flows through UDS inline frames while payload bytes are exchanged via shared memory — zero-copy on the data path.

Rust Native Layer

Performance-critical components are implemented in Rust and compiled as a Python extension via PyO3 + maturin:

• Buddy Allocator — Zero-syscall shared memory allocation for the IPC transport. Cross-process, lock-free on the fast path.
• HTTP Relay — High-throughput axum-based gateway bridging HTTP to IPC. Handles connection pooling and request multiplexing.

The Rust extension is compiled automatically during pip install c-two (from pre-built wheels) or uv sync (from source).

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Installation

From PyPI

pip install c-two

Pre-built wheels are available for:

• Linux: x86_64, aarch64
• macOS: Apple Silicon (aarch64), Intel (x86_64)
• Python: 3.10, 3.11, 3.12, 3.13, 3.14, 3.14t (free-threading)

If no pre-built wheel is available for your platform, pip will build from source (requires a Rust toolchain).

Development Setup

git clone https://github.com/world-in-progress/c-two.git
cd c-two
uv sync          # install dependencies + compile Rust extensions
uv run pytest    # run the test suite

Requires uv and a Rust toolchain.

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Roadmap

Feature	Status
Core RPC framework (CRM / ICRM / Component)	✅ Stable
IPC transport with SHM buddy allocator	✅ Stable
HTTP relay (Rust-powered)	✅ Stable
Chunked streaming (payloads > 256 MB)	✅ Stable
Heartbeat & connection management	✅ Stable
Read/write concurrency control	✅ Stable
CI/CD & multi-platform PyPI publishing	✅ Stable
Async interfaces	🔜 Planned
Disk spill for extreme payloads	✅ Stable
Cross-language clients (Rust/C++)	🔮 Future

See the full roadmap for details.

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License

MIT

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Built for scientific Python. Powered by Rust.