wg

Golang like WaitGroup implementation for sync/async Rust, support no_std environment.

Introduction

wg provides three WaitGroup flavors so you can pick the right synchronization primitive for the context you're in — blocking, async, or lock-free — all with the same add / done / wait / remaining surface.

Status

wg follows Semantic Versioning and has a deliberately narrow scope: three WaitGroup variants (blocking, async, lock-free). The API is considered complete for that scope. Bug fixes, documentation improvements, and small non-breaking additions (trait impls, ergonomic tweaks) are welcome; new features outside the WaitGroup concept are out of scope — use a different primitive.

Which WaitGroup should I use?

Type	When to use	Backed by
wg::WaitGroup	Default choice for synchronous code on std. Blocks the calling thread in wait.	Mutex + Condvar (or parking_lot equivalents)
wg::future::WaitGroup	Async contexts (also support no_std + alloc environments). Works with any async runtime (tokio, smol, …). Exposes wait().await plus a wait_blocking() escape hatch.	event-listener
wg::spin::WaitGroup	no_std + alloc environments, or short waits where you want to avoid OS synchronization.	AtomicUsize with adaptive backoff (yields on std, spins on pure no_std)

All three implement Clone, Debug, Send + Sync, and From<usize>. API is otherwise identical — easy to switch between variants.

Installation

Default build (blocking WaitGroup, std, parking_lot, triomphe):

[dependencies]
wg = "1"

Enable the async variant (wg::future::WaitGroup):

[dependencies]
wg = { version = "1", features = ["future"] }

no_std + alloc build (only wg::spin::WaitGroup and, with future, wg::future::WaitGroup):

[dependencies]
wg = { version = "1", default-features = false, features = ["alloc"] }

# + async:
wg = { version = "1", default-features = false, features = ["alloc", "future"] }

Feature flags

Feature	Default	Description
std	yes	Enables the blocking wg::WaitGroup (uses std::sync).
parking_lot	yes	Switches the blocking variant to parking_lot::{Mutex, Condvar}.
triomphe	yes	Uses triomphe::Arc (no weak refs, smaller footprint).
alloc	no	Required in no_std builds to use spin::WaitGroup / future::WaitGroup.
future	no	Enables wg::future::WaitGroup (event-listener based).

Examples

See examples/ for more.

MSRV

Minimum supported Rust version is 1.76.0. This is dictated by the current parking_lot and triomphe minima; enabling neither feature would drop the floor further. MSRV bumps are considered a breaking change and will require a major version bump.

Acknowledgements

• Inspired by Go's sync.WaitGroup and crossbeam_utils::WaitGroup.

License

wg is under the terms of both the MIT license and the Apache License (Version 2.0).

See LICENSE-APACHE, LICENSE-MIT for details.

Copyright (c) 2026 Al Liu.