smarm

Silly Marks Abstract Rust Machine. A prototype green-thread actor runtime for Rust.

Implements the core ideas in LOOM.md: green-thread actors on a shared heap, scheduled cooperatively, communicating only by Send messages. Erlang's isolation model without Erlang's copying GC, Rust's zero-copy ownership transfers without async's function colouring.

This is single-threaded for now — one scheduler, one OS thread. Multi-threaded scheduling is on the deferred list. The public API is shaped to match what the multi-threaded version will expose, so the migration shouldn't require source changes for downstream code.

What's here

Module	What it does
stack	mmap'd growable stack with guard page; SIGSEGV on overflow
context	#[naked] x86-64 context-switch shims, callee-saved regs only
preempt	Allocator-driven preemption; check!() macro for no-alloc loops
pid	(index, generation) PIDs; stale handles are detectable, not silent
actor	Trampoline + catch_unwind boundary at the actor entry point
scheduler	Run queue, slot table, spawn/join, parking, idle path
channel	Unbounded MPSC channel; recv parks the actor
mutex	Mutex<T> with mandatory timeout; FIFO waiters; parks the green thread
timer	Min-heap of (deadline, reason); Sleep and WaitTimeout reasons
io	block_on_io for blocking work; wait_readable/wait_writable + read/write via epoll
supervisor	Signal::Exit / Signal::Panic delivered to a parent actor's mailbox

Quick taste

use smarm::{run, spawn, channel};

run(|| {
    let (tx, rx) = channel::<i64>();
    let h = spawn(move || {
        for _ in 0..3 {
            let v = rx.recv().unwrap();
            println!("got {v}");
        }
    });
    for v in 1..=3i64 {
        tx.send(v).unwrap();
    }
    h.join().unwrap();
});

Layout

src/
  stack.rs context.rs preempt.rs pid.rs actor.rs
  scheduler.rs channel.rs mutex.rs timer.rs io.rs supervisor.rs
  lib.rs
tests/
  per-module integration tests
benches/
  primes.rs    fan-out/fan-in compute, vs tokio current_thread
LOOM.md        design intent

Building and running

Standard Cargo. Requires Rust 1.95 or newer (the #[naked] attribute went stable in 1.88; we use a few unrelated post-1.88 features). x86-64 Linux only — ARM64 and macOS are on the deferred list because of the assembly shim and the epoll dependency.

cargo test                # all tests
cargo test --test mutex   # one module
cargo bench               # primes benchmark vs tokio

What's not here

See the Defer section of LOOM.md. Notable absences: multi-threaded scheduler, supervisor restart-intensity caps, join! for handle groups, stack growth via remap, hierarchical timer wheel, fd-wait timeouts, Signal::Timeout. Each is mechanism we know how to add; none belongs in this iteration.