lmflow 0.3.3

Dataflow-graph compute engine: a pure-Rust scheduler behind a stable C ABI
Documentation

lmflow

crates.io docs.rs ci license

A dataflow-graph compute engine: a pure-Rust scheduler behind a stable C ABI. Computation is described as a directed graph — nodes are kernels, and timestamped packets flow along the edges.

use lmflow::{register_kernel, Graph, Kernel, KernelCtx, Packet};

#[derive(Default)]
struct Double;
impl Kernel for Double {
    fn process(&mut self, cc: &mut KernelCtx) -> lmflow::Result<()> {
        let v = cc.input(0).and_then(|p| p.as_i64()).unwrap_or(0);
        cc.emit(0, Packet::from_i64(v * 2))
    }
}

register_kernel::<Double>("Double")?;
let g = Graph::from_yaml(yaml)?;

Install

cargo add lmflow

No C++ toolchain required. Kernels are decoupled from the engine: write them in Rust with trait Kernel + register_kernel, or plug C++/Python kernels in through the C ABI (lmflow_register_kernel) — the registry is language-agnostic, and the engine neither knows nor cares what language a kernel is written in.

Full documentation: https://docs.rs/lmflow (this crate) · https://laomou.github.io/lm-flow/ (the whole project: Rust / C++ / Python).

Built-in Rust kernels

Two, registered automatically on graph construction — no setup call needed:

Name What it does Ports
PassThrough zero-copy forward (wiring / placeholder) 1 → 1, any type
Sink consume only, so a branch can terminate itself 1 → 0, any type

Deliberately only these two: both are purely structural, with no assumptions about the payload. Kernels like Scale/Sum/Zip/Filter would have to assume a concrete payload type (i64), which contradicts the engine's design rule that it never interprets payloads. Fan-out needs no kernel either — one edge can feed several consumers natively. Compute is yours to write; the engine provides structure.

Declared in YAML, not in your kernels

Topology, threading and flow-control policy are configuration, not code:

Field What it does
executors thread pools, with optional CPU affinity and real-time priority
input_policy per node: sync (timestamp-aligned), immediate, fixed_size (bounded, drops oldest), sync_set, batch
on_error abort (default) or skip — drop the offending packet, advance the downstream bound, count it and warn, instead of killing the pipeline
rate source pacing in Hz; the engine guarantees the interval, so the kernel needs no timing code
back_edges turn an input port into a latest-value register that is excluded from readiness, termination and alignment — this is what lets a topology contain a cycle
subgraphs / type / include reusable subgraphs, inlined at graph-build time
watchdog_ms, stats, max_queued_* slow-callback warnings, tiered runtime diagnostics, global watermarks

Graph::reset() puts a terminated graph back to a startable state while keeping already-opened kernel instances alive, so an expensive one-off such as loading a model is not repeated per run. Per-node statistics (packets in/out, invocations, errors, peak queue depth, processing time) and Graph::to_dot() — with an optional latency heat map — cover observability.

Configuration that asks for something unimplemented is rejected loudly at graph construction rather than ignored: silently doing less than the config asked for is the one failure mode that cannot be debugged from the outside.

The same engine is also consumed from C/C++ (#include "lmflow/flow.h", link liblmflow.a), Python (pip install lm-lmflow), and mobile (Android / iOS / HarmonyOS bridges). See the repository for the native SDK and the 18 bundled C++ kernels — those live outside this crate and are not distributed with it.

License: Apache-2.0.