Memory leak through FuncDataRegistry when repeatedly instantiating module

[matklad]

Describe the bug

The following code:

let module = wasmer::Module::new(&store, &wasm).unwrap();
loop {
  let imports = ...;
  let instance = wasmer::Instance::new(&module, &imports).unwrap();
}

uses unbounded amount of memory

Steps to reproduce

Full repro is here: https://github.com/matklad/repros/blob/9f98e5cda5a54a7242ba2b3c39b1a36bee5d4404/wasmer-leak/src/main.rs

Expected behavior

Bounded memory usage

Actual behavior

Memory usage increases without bound

Additional context

Reproduces this with both wasmer2 and current master. The culprit is this data structure:

wasmer/lib/engine-universal/src/artifact.rs

Line 42 in e389ad0

func_data_registry: Arc<FuncDataRegistry>,

This is a hashmap keyed by addresses of all imported functions. It is a part of Store, so it is shared across all Instances we create. The hashmap is append only and never shrinks, so it accumulates imports from long-dead instances.

[syrusakbary]

Related PR: #2437

[syrusakbary]

Thanks to #2699 we now don't leak the function references by default to the store.

This means that if the Wasm is not using reference types, the functions are not stored in the store, and therefore not leaked anywhere.
However, if the funcrefs are used this will be registered in the store until the store drops.