# Objective
Fix some grammatical errors: it's -> its
Not the most useful commit in the world, but I saw a couple of these and
decided to fix the lot.
## Solution
-
## Testing
-
# Objective
Now that `bevy_platform::cfg` is merged, we can start tidying up
features. This PR starts with `bevy_utils`.
## Solution
- Removed `serde` and `critical-section` features (they were just
re-exports of `bevy_platform` anyway)
- Removed `std`, `alloc` features, relying on `bevy_platform::cfg` to
check for availability.
- Added `parallel` feature to provide access to the `Parallel` type.
- Moved the `HashMap` type aliases into `map.rs` for better
organisation.
## Testing
- CI
# Background
In `no_std` compatible crates, there is often an `std` feature which
will allow access to the standard library. Currently, with the `std`
feature _enabled_, the
[`std::prelude`](https://doc.rust-lang.org/std/prelude/index.html) is
implicitly imported in all modules. With the feature _disabled_, instead
the [`core::prelude`](https://doc.rust-lang.org/core/prelude/index.html)
is implicitly imported. This creates a subtle and pervasive issue where
`alloc` items _may_ be implicitly included (if `std` is enabled), or
must be explicitly included (if `std` is not enabled).
# Objective
- Make the implicit imports for `no_std` crates consistent regardless of
what features are/not enabled.
## Solution
- Replace the `cfg_attr` "double negative" `no_std` attribute with
conditional compilation to _include_ `std` as an external crate.
```rust
// Before
#![cfg_attr(not(feature = "std"), no_std)]
// After
#![no_std]
#[cfg(feature = "std")]
extern crate std;
```
- Fix imports that are currently broken but are only now visible with
the above fix.
## Testing
- CI
## Notes
I had previously used the "double negative" version of `no_std` based on
general consensus that it was "cleaner" within the Rust embedded
community. However, this implicit prelude issue likely was considered
when forming this consensus. I believe the reason why is the items most
affected by this issue are provided by the `alloc` crate, which is
rarely used within embedded but extensively used within Bevy.
# Objective
- Adjust `bevy_utils` to make it `no_std` compatible
- Partially replaces #6581
- Contributes to #8161
- Contributes to #6370
## Solution
Added `alloc` and `std` features to `bevy_utils` (`std` is enabled by
default), allowing the crate's use in `no_std` contexts.
## Testing
- CI passed locally.
- Used `bevy_utils` in a `no_std` crate as an experiment and compiled
successfully.
## Migration Guide
If you were importing `bevy_utils` and setting `default_features` to
`false`, but relying on elements which are now gated behind the `std` or
`alloc` features, include the relevant feature in your `Cargo.toml`.
## Notes
- Bevy already includes a single `no_std` crate, `bevy_ptr`, so there is
precedent for this change.
- As `bevy_utils` is widely used across the rest of Bevy, further work
to make Bevy `no_std` compatible would be blocked on this crate, if such
work was to be undertaken.
- Most of the changes in this PR are just the removal of an unnecessary
call to `to_string()` within unit tests.
# Objective
- `Parallel::drain()` has an unused type parameter `B` than can be
removed.
- Caught [on
Discord](https://discord.com/channels/691052431525675048/692572690833473578/1259004180560085003)
by Andrew, thanks!
## Solution
- Remove it! :)
## Testing
- `Parallel::drain()` should still function exactly the same.
---
## Changelog
- Removed unused type parameter in `Parallel::drain()`.
## Migration Guide
The type parameter of `Parallel::drain()` was unused, so it is now
removed. If you were manually specifying it, you can remove the bounds.
```rust
// 0.14
// Create a `Parallel` and give it a value.
let mut parallel: Parallel<Vec<u8>> = Parallel::default();
*parallel.borrow_local_mut() = vec![1, 2, 3];
for v in parallel.drain::<u8>() {
// ...
}
// 0.15
let mut parallel: Parallel<Vec<u8>> = Parallel::default();
*parallel.borrow_local_mut() = vec![1, 2, 3];
// Remove the type parameter.
for v in parallel.drain() {
// ...
}
```
# Objective
- bevy usually use `Parallel::scope` to collect items from `par_iter`,
but `scope` will be called with every satifified items. it will cause a
lot of unnecessary lookup.
## Solution
- similar to Rayon ,we introduce `for_each_init` for `par_iter` which
only be invoked when spawn a task for a group of items.
---
## Changelog
- added `for_each_init`
## Performance
`check_visibility ` in `many_foxes `
~40% performance gain in `check_visibility`.
---------
Co-authored-by: James Liu <contact@jamessliu.com>
# Objective
There's a repeating pattern of `ThreadLocal<Cell<Vec<T>>>` which is very
useful for low overhead, low contention multithreaded queues that have
cropped up in a few places in the engine. This pattern is surprisingly
useful when building deferred mutation across multiple threads, as noted
by it's use in `ParallelCommands`.
However, `ThreadLocal<Cell<Vec<T>>>` is not only a mouthful, it's also
hard to ensure the thread-local queue is replaced after it's been
temporarily removed from the `Cell`.
## Solution
Wrap the pattern into `bevy_utils::Parallel<T>` which codifies the
entire pattern and ensures the user follows the contract. Instead of
fetching indivdual cells, removing the value, mutating it, and replacing
it, `Parallel::get` returns a `ParRef<'a, T>` which contains the
temporarily removed value and a reference back to the cell, and will
write the mutated value back to the cell upon being dropped.
I would like to use this to simplify the remaining part of #4899 that
has not been adopted/merged.
---
## Changelog
TODO
---------
Co-authored-by: Joseph <21144246+JoJoJet@users.noreply.github.com>
