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
• async/await support and .Then API
• Thread safe
• Full causality traces
• Easily switch to foreground or background context
• Combine async operations
• Circular await detection
• 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:

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

• Fixed Promise.ParallelFor* canceling workers too early.
• Promise.ParallelFor* and AsyncEnumerable.Merge propagate exceptions from cancelation token callbacks instead of deadlocking.
• AsyncEnumerable.Merge more eagerly stops iteration if a rejection or cancelation occurs.

See ChangeLog for the full changelog.

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