Crate lunatic[−][src]

Expand description

Helper library for building Rust applications that run on Lunatic.

Main concepts

The main abstraction in Lunatic is a Process. Contrary to operating system processes, lunatic processes are lightweight and fast to spawn. They are designed for MASSIVE concurrency.

Processes can be spawned from just a function:

use lunatic::{process, Mailbox};

process::spawn(|_: Mailbox<()>| {
    println!("Hi! I'm a process.");
})
.unwrap()
.join()
.unwrap();

One important characteristic of processes is that they are sandboxed. Each of them gets a separate memory and they can’t access any memory from the parent, not even through raw pointer access. If we need to pass any information to the newly spawned process we can do it through a context:

use lunatic::{process, Mailbox};

let proc = "Process";
process::spawn_with(proc.to_string(), |proc, _: Mailbox<()>| {
    // This closure gets a new heap and stack to execute on,
    // and can't access the memory of the parent process.
    println!("Hello {}!", proc);
})
.unwrap()
.join()
.unwrap();

Messaging

Processes can exchange information with each other through messages:

use lunatic::process;

let proc = process::spawn(|mailbox| {
    let message = mailbox.receive();
    println!("Hello {}", message);
})
.unwrap();

proc.send("World!".to_string());
proc.join().unwrap();

Most types should automatically implement the Message trait, but for custom types a #[derive(lunatic::derive::Message)] helper can be used.

Each process gets a Mailbox as an argument to the entry function. Mailboxes can be used to receive messages. If there are no messages in the mailbox the process will block on receive until a message arrives.

Linking

Processes can be linked together. This means that if one of them fails, all the ones linked to it will get notified. A linked process can be spawned with the process::spawn_link function. The function will take the current Mailbox and return a LinkMailbox, that will also receive notifications about linked processes. If we would like to automatically fail as soon as one of the linked processes fails, we can turn the LinkMailbox back to a regular one with the panic_if_child_panics() function.

use lunatic::{process, Mailbox};

fn main() {
    process::spawn(|mailbox: Mailbox<()>| {
        let (_child, mailbox) = process::spawn_link(mailbox, child).unwrap();
        // Wait on message
        assert_eq!(mailbox.receive().is_err(), true);
    })
    .unwrap()
    .join()
    .unwrap();
}

fn child(_: Mailbox<()>) {
    panic!("Error");
}

Sandboxing

A Environment can define characteristics that processes spawned into it have. The environment can limit:

Memory usage
Compute usage
WebAssembly host function (syscalls) access

An Environment is configured through a Config.

use lunatic::{Config, Environment, Mailbox};

// Create a new environment where processes can use maximum 17 Wasm pages of
// memory (17 * 64KB) & 1 gallon of instructions (~=100k CPU cycles).
let config = Config::new(17, Some(1));
// Allow only syscalls under the "wasi_snapshot_preview1::environ*" namespace
config.allow_namespace("wasi_snapshot_preview1::environ");
let env = Environment::new(config).unwrap();
let module = env.add_this_module().unwrap();

// This process will fail because it can't uses syscalls for std i/o
let proc = module
    .spawn(|_: Mailbox<()>| {
        println!("Hi from different env");
    })
    .unwrap()
    .join();
assert_eq!(proc.is_err(), true);

// This process will fail because it uses too much memory
let proc = module
    .spawn(|_: Mailbox<()>| {
        vec![0; 15_000];
    })
    .unwrap()
    .join();
assert_eq!(proc.is_err(), true);

// This process will fail because it uses too much compute
let proc = module
    .spawn(|_: Mailbox<()>| loop {
        let _ = 1 + 1;
    })
    .unwrap()
    .join();
assert_eq!(proc.is_err(), true);

Loading other WebAssembly modules

Lunatic allows for dynamic loading of other WebAssembly modules during runtime. Environment::add_module can be used to add WebAssembly modules to an environment.

Setting up Cargo for lunatic

To simplify developing, testing and running lunatic applications with cargo, you can add a .cargo/config.toml file to your project with the following content:

[build]
target = "wasm32-wasi"

[target.wasm32-wasi]
runner = "lunatic"

Now you can just use the commands you were already familiar with, such as cargo run, cargo test and cargo is going to automatically build your project as a WebAssembly module and run it inside of lunatic.

Debugging

If a process dies, either because an unsupported syscall was called or a Kill signal was received there is not going to be any output in the terminal. To get more insight set the RUST_LOG environment variable to lunatic=debug. E.g. RUST_LOG=lunatic=debug cargo run.