Crate compact_waitgroup 

A compact asynchronous WaitGroup synchronization primitive.

This crate is designed to be lightweight and executor-agnostic. It works with any async runtime and supports no_std environments (requires alloc).

Usage

MonoWaitGroup

use compact_waitgroup::MonoWaitGroup;

let (wg, token) = MonoWaitGroup::new();
assert!(!wg.is_done());

std::thread::spawn(move || {
    // Long-running task
    token.release();
});

// Wait for the task to complete
wg.await;

WaitGroup

use compact_waitgroup::WaitGroup;

let (wg, factory) = WaitGroup::new();

factory.scope(|token| {
    let token_cloned = token.clone();
    std::thread::spawn(move || {
        // Long-running task
        token_cloned.release();
    });
    std::thread::spawn(move || {
        // Another long-running task
        token.release();
    });
});

// Wait for all tasks to complete
wg.await;

With async Runtime

use compact_waitgroup::{GroupTokenExt, WaitGroup};

let (wg, factory) = WaitGroup::new();

for (i, token) in std::iter::repeat_n(factory.into_token(), 8).enumerate() {
    let task = async move {
        println!("Task {i} started");
        // Long-running task...
        sleep(std::time::Duration::from_secs(1)).await;
        println!("Task {i} finished");
    };
    spawn(task.release_on_ready(token));
}

// Wait for all tasks to complete
wg.await;

Memory Layout

This crate is designed to be extremely lightweight. The memory footprint depends on the architecture and the enabled features.

By default, MonoWaitGroup shares the same underlying memory structure as WaitGroup. However, this means MonoWaitGroup carries a usize field for reference counting of workers, which is redundant for the singly-owned MonoGroupToken.

Enabling the compact-mono feature changes the internal definition of MonoWaitGroup. It switches to a dedicated, stripped-down layout that removes the reference counter.

Component	Default (64-bit)	With compact-mono	Saving
WaitGroup	32 bytes	32 bytes	0 bytes
MonoWaitGroup	32 bytes	24 bytes	8 bytes

Structs

GroupToken

Clonable group token.

GroupTokenFactory

Factory of GroupToken.

GroupTokenReleaseOnDrop

Wrapper that releases a token when the future is dropped.

GroupTokenReleaseOnReady

Wrapper that releases a token when the future is ready or dropped.

MonoGroupToken

Non-clonable group token.

MonoWaitGroup

WaitGroup with a single non-clonable group token.

WaitGroup

WaitGroup with clonable group tokens.

Traits

GroupTokenExt

Extension trait for futures to automatically release group tokens.

GroupTokenFuncExt

Extension trait for FnOnce to automatically release group tokens.