ProtoPromise

Robust and efficient library for management of asynchronous operations.

• Allocation-free async operations
• Cancelable operations with custom allocation-free CancelationToken/Source
• Allocation-free async iterators with async Linq
• Progress with enforced normalization
• Structured concurrency
• async/await support and .Then API
• Thread safe
• Easily switch to foreground or background context
• Circular await detection
• Full causality traces
• Interoperable with Tasks and Unity's Coroutines/Awaitables
• CLS compliant

ProtoPromise conforms to the Promises/A+ Spec as far as is possible with C# (using static typing instead of dynamic), and further extends it to support Cancelations and Progress.

This library was built to work in all C#/.Net ecosystems, including Unity, Mono, .Net Framework, .Net Core, and AOT compilation. It is CLS compliant, so it is not restricted to only C#, and will work with any .Net language.

• ProtoPromise v3 supports .Net Standard 2.0 or newer (Unity 2018.3 or newer).
• ProtoPromise v2 supports .Net 3.5 or newer (Unity 5.5 or newer).

See Guides for information on how to install and use this library.

Compare performance to other async libraries:

Type	Pending	Mean	Allocated	Survived
ProtoPromise	False	37.56 ns	-	-
Task	False	49.97 ns	192 B	-
UniTask	False	81.06 ns	-	-
UnityFxAsync	False	62.05 ns	360 B	-
ValueTask	False	70.66 ns	-	-
ProtoPromise	True	401.37 ns	-	624 B
Task	True	455.15 ns	1120 B	-
UniTask	True	478.92 ns	-	744 B
UnityFxAsync	True	433.54 ns	1952 B	-
ValueTask	True	498.24 ns	968 B	40 B

See the C# Asynchronous Benchmarks Repo for a full performance comparison.

Latest Updates

v3.3.0 - January 27, 2025

• Added Proto.Timers and time-based APIs.
• Added CancelationToken(bool) constructor and CancelationToken.RegisterWithoutImmediateInvoke APIs.
• Added PromiseYielder.Initialize() API to help with early code running before Unity can auto initialize.
• Fixed Unity initialization not being fully initialized before user Awake methods run.
• Reduced memory and increased speed.
• Deprecated several APIs.

See ChangeLog for the full changelog.

Acknowledgements

This library was inspired by ES6 Promises, RSG Promises, uPromise, TPL, UniTask, AsyncEx, and UnityAsync.