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Update init_resource to not overwrite #1349

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merged 5 commits into from
Jan 30, 2021
Merged

Update init_resource to not overwrite #1349

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b8c790b
Update init_resource to not overwrite
DJMcNab Jan 29, 2021
dc1a26e
Don't double check for init_resources
DJMcNab Jan 29, 2021
d749b51
Fix incorrect conditions
DJMcNab Jan 29, 2021
e231ada
Add comment about double hashing
DJMcNab Jan 30, 2021
bdc4f3c
add PERF label
cart Jan 30, 2021
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16 changes: 12 additions & 4 deletions crates/bevy_app/src/app_builder.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -235,8 +235,13 @@ impl AppBuilder {
where
R: FromResources + Send + Sync + 'static,
{
let resource = R::from_resources(&self.app.resources);
self.app.resources.insert(resource);
// We could avoid double hashing here, since the `from_resources` call is guaranteed not to
// modify the map. However, we would need to be borrowing resources both mutably and immutably,
// so we would need to be extremely certain this is correct
if !self.resources().contains::<R>() {
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This does "double hash" the type id. Resources don't currently have an "entry" api. And I don't think adding one is in scope for this pr. But can we add a // PERF: remove this double hash comment so it is discoverable?

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That would be difficult in this case, because we need to both be modifying self.resources() for the Entry, and reading it for the from_resources call - so without some gnarly unsafe code, I'm not sure this is feasible.
It's also worth noting that this is using the bevy_utils::HashMap, so the hashing is rather cheap.
Also this only happens at app startup time, so the cost doesn't matter too much. I've added a comment explaining this though

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makes sense. i added a "PERF" label here. I use those like TODO labels, but for places where we are knowingly leaving perf on the table.

let resource = R::from_resources(&self.resources());
self.add_resource(resource);
}

self
}
Expand All @@ -245,8 +250,11 @@ impl AppBuilder {
where
R: FromResources + 'static,
{
let resource = R::from_resources(&self.app.resources);
self.app.resources.insert_thread_local(resource);
// See perf comment in init_resource
if self.app.resources.get_thread_local::<R>().is_none() {
let resource = R::from_resources(&self.app.resources);
self.app.resources.insert_thread_local(resource);
}

self
}
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4 changes: 1 addition & 3 deletions crates/bevy_render/src/lib.rs
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Expand Up @@ -177,9 +177,7 @@ impl Plugin for RenderPlugin {
shader::clear_shader_defs_system.system(),
);

if app.resources().get::<Msaa>().is_none() {
app.init_resource::<Msaa>();
}
app.init_resource::<Msaa>();

if let Some(ref config) = self.base_render_graph_config {
let resources = app.resources();
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