Crate pyodide_webassembly_runtime_layer

pyodide-webassembly-runtime-layer implements the wasm_runtime_layer backend API to provide access to the web browser’s WebAssembly runtime using Pyodide.

The implementation of this crate is heavily inspired by the web_backend of the wasm_runtime_layer. Instead of relying on the js-sys and wasm-bindgen crates to generate JavaScript-based bindings to the WebAssembly JavaScript API, this crate uses Pyodide’s js FFI layer to interact with WebAssembly through Python running inside WASM. pyodide-webassembly-runtime-layer is therefore useful when developing a Python module in Rust, e.g. using PyO3, which requires access to some WASM runtime using the wasm_runtime_layer API and may be deployed to the web itself using Pyodide.

Memory Management

pyodide-webassembly-runtime-layer generally tries to keep memory management intuitive by relying primarily on Python’s reference counting to drop objects once they are no longer needed by both the user-written Rust code and the WebAssembly runtime. As this crate coordinates interop across Rust, Python, and JavaScript, it takes extra care to avoid reference cycles across the different memory management strategies of the languages which would otherwise lead to memory leakage. If using this crate produces a memory leak that is avoided with a different wasm_runtime_layer backend, please report it as a bug.

There is one exception to the intuitive memory management strategy:

• Func::new creates a host function, which may capture arbitrary data. To avoid cross-language reference cycles, it is stored using wobbly references inside the Func and its associated Store. Even though the host function and its data are dropped once either the Store is dropped or references to the Func are dropped, additional bookkeeping data is required until both have been dropped.

Structs

• Engine
  Runtime for WebAssembly web runtime.
• ExternRef
  Extern host reference type.
• Func
  A bound function, which may be an export from a WASM Instance or a host function.
• Global
  A global variable accesible as an import or export in a module.
• Instance
  An instantiated instance of a WASM Module.
• Memory
  A WASM memory.
• Module
  A WASM module.
• Store
  A store for the Engine, which stores host-defined data T and internal state.
• StoreContext
  Immutable context to the store
• StoreContextMut
  Mutable context to the store
• Table
  A WASM table.