Python cooperative threading

This component exercises Python’s built-in threading module through jco’s extended suite: thread start/join and sleep, a contended lock, condition notification, and thread-local values/identities across a barrier. Worker exceptions are propagated to the exported call. The host runs each case twice on the same instance and enforces a subprocess deadline for deadlocks.

The start/join case is adapted from componentize-py’s multithreading examplegithub and its upstream testgithub. The synchronization cases are new. The upstream example’s printing is replaced with a returned trace, and assertions allow different timer wakeup orders.

Toolchain

As of 2026-10-29, cooperative threading is in the open componentize-py PR #242, not upstream main or a released wheel. just setup pins revision e520f231f761d771f30224096e4f972fcaaa9c62 and Rust nightly-2026-10-08. The PR downloads its matching CPython build and WASI SDK 34 fork with shared library exception support. A stock SDK 34 installation alone is insufficient to build this version of componentize-py. The setup recipe clears CC, CXX, WASI_SDK_PATH, and WASI_SDK_VERSION for the Cargo install. This lets native dependencies use host compilers and upstream select its matching SDK, even when the WASI SDK setup action has exported WebAssembly compiler overrides.

From the repository root:

just -f test/components/python/coop-threading/justfile setup
just -f test/components/justfile build-python-coop-threading
pnpm --filter '@bytecodealliance/jco-transpile' test:extended python-coop-threading

The source build requires Cargo, rustup, a native C/C++ toolchain, and network access for dependencies. CI caches the resulting binary. To use an already built binary, skip setup and set COMPONENTIZE_PY to its absolute path. The build always passes --target wasm32-wasip3-threads; an older tool fails instead of silently building a non-threaded component.

Replace the source pin with a released componentize-py once the target ships.