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# Objective - Fixes #15460 (will open new issues for further `no_std` efforts) - Supersedes #17715 ## Solution - Threaded in new features as required - Made certain crates optional but default enabled - Removed `compile-check-no-std` from internal `ci` tool since GitHub CI can now simply check `bevy` itself now - Added CI task to check `bevy` on `thumbv6m-none-eabi` to ensure `portable-atomic` support is still valid [^1] [^1]: This may be controversial, since it could be interpreted as implying Bevy will maintain support for `thumbv6m-none-eabi` going forward. In reality, just like `x86_64-unknown-none`, this is a [canary](https://en.wiktionary.org/wiki/canary_in_a_coal_mine) target to make it clear when `portable-atomic` no longer works as intended (fixing atomic support on atomically challenged platforms). If a PR comes through and makes supporting this class of platforms impossible, then this CI task can be removed. I however wager this won't be a problem. ## Testing - CI --- ## Release Notes Bevy now has support for `no_std` directly from the `bevy` crate. Users can disable default features and enable a new `default_no_std` feature instead, allowing `bevy` to be used in `no_std` applications and libraries. ```toml # Bevy for `no_std` platforms bevy = { version = "0.16", default-features = false, features = ["default_no_std"] } ``` `default_no_std` enables certain required features, such as `libm` and `critical-section`, and as many optional crates as possible (currently just `bevy_state`). For atomically-challenged platforms such as the Raspberry Pi Pico, `portable-atomic` will be used automatically. For library authors, we recommend depending on `bevy` with `default-features = false` to allow `std` and `no_std` users to both depend on your crate. Here are some recommended features a library crate may want to expose: ```toml [features] # Most users will be on a platform which has `std` and can use the more-powerful `async_executor`. default = ["std", "async_executor"] # Features for typical platforms. std = ["bevy/std"] async_executor = ["bevy/async_executor"] # Features for `no_std` platforms. libm = ["bevy/libm"] critical-section = ["bevy/critical-section"] [dependencies] # We disable default features to ensure we don't accidentally enable `std` on `no_std` targets, for example. bevy = { version = "0.16", default-features = false } ``` While this is verbose, it gives the maximum control to end-users to decide how they wish to use Bevy on their platform. We encourage library authors to experiment with `no_std` support. For libraries relying exclusively on `bevy` and no other dependencies, it may be as simple as adding `#![no_std]` to your `lib.rs` and exposing features as above! Bevy can also provide many `std` types, such as `HashMap`, `Mutex`, and `Instant` on all platforms. See `bevy::platform_support` for details on what's available out of the box! ## Migration Guide - If you were previously relying on `bevy` with default features disabled, you may need to enable the `std` and `async_executor` features. - `bevy_reflect` has had its `bevy` feature removed. If you were relying on this feature, simply enable `smallvec` and `smol_str` instead. --------- Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com> |
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Bevy Tasks
A refreshingly simple task executor for bevy. :)
This is a simple threadpool with minimal dependencies. The main usecase is a scoped fork-join, i.e. spawning tasks from
a single thread and having that thread await the completion of those tasks. This is intended specifically for
bevy as a lighter alternative to rayon for this specific usecase. There are also utilities for
generating the tasks from a slice of data. This library is intended for games and makes no attempt to ensure fairness
or ordering of spawned tasks.
It is based on async-executor, a lightweight executor that allows the end user to manage their own threads.
async-executor is based on async-task, a core piece of async-std.
Usage
In order to be able to optimize task execution in multi-threaded environments, bevy provides three different thread pools via which tasks of different kinds can be spawned. (The same API is used in single-threaded environments, even if execution is limited to a single thread. This currently applies to Wasm targets.) The determining factor for what kind of work should go in each pool is latency requirements:
-
For CPU-intensive work (tasks that generally spin until completion) we have a standard [
ComputeTaskPool] and an [AsyncComputeTaskPool]. Work that does not need to be completed to present the next frame should go to the [AsyncComputeTaskPool]. -
For IO-intensive work (tasks that spend very little time in a "woken" state) we have an [
IoTaskPool] whose tasks are expected to complete very quickly. Generally speaking, they should just await receiving data from somewhere (i.e. disk) and signal other systems when the data is ready for consumption. (likely via channels)
no_std Support
To enable no_std support in this crate, you will need to disable default features, and enable the edge_executor and critical-section features.