Remove IDs and Registries

[nical]

This is a meta issue to describe the long-ish term vision for wgpu-core's resource management and track the steps towards it.

Registries and IDs

Internally, all wgpu-core resources are stored behind Arcs. Externally, they are exposed as non-clonable structs containing an ID which conceptually corresponds to a single reference to the Arc of a resource.

The goal

Instead of having wgpu public types wrap a non-clonabe ID, we would like them to wrap the Arc to the internal resource directly (and be clonable).

TODO

• Resolve cycles in wgpu-core using weak references #5120
• (Firefox): Move the wgpu-core part of command recording out of the content process
• Remove remaining internal use of the IDs.
• Make wgpu-core less generic (brainstorm) #5124
• (Firefox): Stop providing the IDs during resource creation and do ID mapping in the gecko-side bindings.
• Move logic present in the Global's methods into methods on wgpu-core objects
• Rewrite the record-reply functionality Add back support for tracing (trace feature) to wgpu #5974
• Remove the registries

[sagudev]

(Firefox): Stop providing the IDs during resource creation and do ID mapping in the gecko-side bindings.

How exactly would that look like? Would that be something like hashmap that would map id to Arc of wgpu object that would live in WebGPU thread?

I'm mostly asking for servo, as it would be nice to share ID mapping stuff.

[nical]

(Firefox): Stop providing the IDs during resource creation and do ID mapping in the gecko-side bindings.

How exactly would that look like? Would that be something like hashmap that would map id to Arc of wgpu object that would live in WebGPU thread?

Yes, that's the general idea. Depending on how you generate the IDs you could get away with arrays instead of hash maps (like wgpu-core currently does).

[sagudev]

There are some cases where this would also be useful in servo, for example when doing swapchain present we always need to send new encoder id from content process so we can create new encoder in wgpu_thread, but removing registries would allow us to have concept of wgc types that are not owned by JS (content process).

I think making descriptors generic over IDs/Arced Resources would be beneficial as that would allow servo to still reuse such types for IPC. Something like this is already done in some parts using Arc* variants descriptors:

wgpu/wgpu-core/src/command/timestamp_writes.rs

Lines 8 to 25 in ad194a8

	pub struct PassTimestampWrites {
	/// The query set to write the timestamps to.
	pub query_set: id::QuerySetId,
	/// The index of the query set at which a start timestamp of this pass is written, if any.
	pub beginning_of_pass_write_index: Option<u32>,
	/// The index of the query set at which an end timestamp of this pass is written, if any.
	pub end_of_pass_write_index: Option<u32>,
	}
	/// Describes the writing of timestamp values in a render or compute pass with the query set resolved.
	pub struct ArcPassTimestampWrites {
	/// The query set to write the timestamps to.
	pub query_set: Arc<crate::resource::QuerySet>,
	/// The index of the query set at which a start timestamp of this pass is written, if any.
	pub beginning_of_pass_write_index: Option<u32>,
	/// The index of the query set at which an end timestamp of this pass is written, if any.
	pub end_of_pass_write_index: Option<u32>,
	}