Remove Sync bound on Component and Resource (adopted) #5879

JohnTheCoolingFan · 2022-09-04T18:52:41Z

Adoption of #4680

Objective

Fixes #2487. Remove the Sync bound on Component and Resource to allow Send-only components.

Solution

Remove Sync bound from Component and Resource.
Address the compilation errors.
Changed the PhantomData<T> in FetchState and SystemParamState to use PhantomData<fn() -> T> to ensure they're Sync.
Add a compile_fail_test.
Add Sync bound on the WorldQuery impl for &T.
Add Sync bound on Res<T> and Option<Res<T>>
Add Sync bound on Query::get_component, World::get, EntityRef::get, and EntityMut::get.

Changelog

Removed: Sync bound on Component and Resource.

Migration Guide

Component and Resource no longer requires Sync. Any generic code using Component as a bound, &T as Query parameter, or Res<T> might require an additional Sync bound.

JohnTheCoolingFan · 2022-09-04T19:11:09Z

Currently working on resolving merge conflicts

alice-i-cecile · 2022-09-04T20:47:26Z

Sounds good :) Let us know if you have any questions or need help.

bjorn3 · 2022-09-05T13:12:43Z

crates/bevy_ecs/src/schedule/stage.rs

@@ -25,7 +25,7 @@ use std::fmt::Debug;
 use super::IntoSystemDescriptor;

 /// A type that can run as a step of a [`Schedule`](super::Schedule).
-pub trait Stage: Downcast + Send + Sync {
+pub trait Stage: Downcast + Send {


Doesn't schedule.get_stage() depend on stages being Sync?

Same for .iter_stages().

bjorn3 · 2022-09-05T13:16:56Z

crates/bevy_ecs/src/world/mod.rs

@@ -1385,7 +1402,7 @@ impl World {
    #[inline]
    pub fn get_resource_by_id(&self, component_id: ComponentId) -> Option<Ptr<'_>> {
        let info = self.components.get_info(component_id)?;
-        if !info.is_send_and_sync() {
+        if !info.is_send() {


This should check for sync, right?

JohnTheCoolingFan · 2022-09-05T16:43:07Z

Currently can't figure out how to make impl WorldQuery for &mut T for !Sync T

BoxyUwU · 2022-09-05T17:10:56Z

crates/bevy_ecs/src/query/fetch.rs

+/// Non-`Sync` components are supported, but cannot be accessed as `&T`,
+/// as the type cannot be safely read from multiple threads at the same
+/// time. These components must be accessed via a `&mut T` to guarentee
+/// that the system has exclusive access to the components.


this isnt going to work and imo is flawed anyway, why shouldn't you be able to use &T from multiple places in a system?
imo we should do one of:

Add NonSync versions of &T and &mut T, leaving the existing types requiring T: Sync

Remove T: Sync bound from &T and &mut T worldqueries (this is a bad idea since now we're going to be registering almost eveyr component as !Sync)

Add a NonSync<T> and use that as the readonly version of &mut T (this is a bad idea since its going to screw up the Query::to_readonly effort by making the readonly version of Query<&mut T> not be Query<&T>)

I am assuming here that the scheduler is smart enough to know not to schedule two systems with read only access of a !Sync component in parallel, if not that should be fixed

Why not just add NonSyncRead<T> for the 'use &T from multiple places in a system' case?

Fundamentally, &mut T requiring T: Sync is entirely superfluous - the requirement that T is Sync would never be used.

Oh I see, because we need to convert to readonly. That's annoying.
I don't suppose we can gate a readonly conversion existing on T being Sync? Is conversion to readonly really a fundamental part of the Query API?

conversion to readonly doesnt require it. we could after all set the readonly version of &mut T to be NonSync<T>. It's just kinda silly to have the readonly version of &mut T not be &T.

Is conversion to readonly really a fundamental part of the Query API?

I think so? It's not quite there yet but I hope that in a bit of time we'll have much more flexibility around changing the Q/F generics and being able to downgrade a query to readonly is a part of that. Personally I value to_readonly working on everything a lot more than some extreme edge case of non sync components needing to use NonSyncMut<T> instead of &mut T

BoxyUwU · 2022-10-17T19:06:41Z

@JohnTheCoolingFan are you still working on this? I'd like to get !Send !Sync components implemented to make World: !Send + !Sync a more usable option for solving some other bevy issues

JohnTheCoolingFan · 2022-10-17T19:37:05Z

No, I just resolved the merge conflicts in an attempt to bring some attention and possibly merge. I now realise that I do not have the knowledge and skills to further maintain this PR.
@BoxyUwU

BoxyUwU · 2022-10-18T01:51:13Z

I'll make a PR for this then 👍

james7132 added 17 commits May 6, 2022 13:19

Bare minimum: Get it to compile

87ec70a

Update bounds on Query/World/Entity{Ref/Mut}

16e86ac

Add compile_fail_test and update Component derive macro

998b4bf

Formatting

dd6fcd3

unsafe impl -> PhantomData<fn() -> T>

f101e84

Fix examples

61f4d7c

Fix examples

01669da

Update paths for compile tests

62d0c4b

Attempt removing Sync on Resource

4feca9d

Formatting k

3f7a0a3

Remaining unsafe impl

6deee18

Use TRYBUILD='overwrite'

7b40740

Convert compile_fail_tests to doctests

dd63b22

Add error codes for compile_fail tests

e6cb45c

Merge branch 'main' into relax-sync-bound

f5b2b4b

Remove unecessary bounds

f1e3983

is_send_and_sync -> is_send

6251294

alice-i-cecile added A-ECS Entities, components, systems, and events C-Usability A targeted quality-of-life change that makes Bevy easier to use labels Sep 4, 2022

alice-i-cecile requested review from BoxyUwU and DJMcNab September 4, 2022 20:46

alice-i-cecile mentioned this pull request Sep 4, 2022

Remove Sync bound on Component and Resource #4680

Closed

Merge branch 'relax-sync-bound'

799f197

bjorn3 reviewed Sep 5, 2022

View reviewed changes

JohnTheCoolingFan added 3 commits September 5, 2022 16:29

Add a Sync bound on impl Plugin for CameraProjectionPlugin

25f5b80

Add a Sync bound on ExtractResource::Source

02c35f9

Remove Sync bound in impl WorldQuery for &mut T

b8ca58a

BoxyUwU reviewed Sep 5, 2022

View reviewed changes

alice-i-cecile added the S-Adopt-Me The original PR author has no intent to complete this work. Pick me up! label Oct 17, 2022

BoxyUwU removed the S-Adopt-Me The original PR author has no intent to complete this work. Pick me up! label Oct 18, 2022

alice-i-cecile closed this Oct 18, 2022

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Remove Sync bound on Component and Resource (adopted) #5879

Remove Sync bound on Component and Resource (adopted) #5879

JohnTheCoolingFan commented Sep 4, 2022

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BoxyUwU commented Oct 18, 2022

Remove Sync bound on Component and Resource (adopted) #5879

Remove Sync bound on Component and Resource (adopted) #5879

Conversation

JohnTheCoolingFan commented Sep 4, 2022

Objective

Solution

Changelog

Migration Guide

JohnTheCoolingFan commented Sep 4, 2022

alice-i-cecile commented Sep 4, 2022

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