[40.0.0] trap on blocking call in sync task before return #12144
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) * trap on blocking call in sync task before return This implements a spec change (PR pending) such that tasks created for calls to synchronous exports may not call potentially-blocking imports or return `wait` or `poll` callback codes prior to returning a value. Specifically, the following are prohibited in that scenario: - returning callback-code.{wait,poll} - sync calling an async import - sync calling subtask.cancel - sync calling {stream,future}.{read,write} - sync calling {stream,future}.cancel-{read,write} - calling waitable-set.{wait,poll} - calling thread.suspend This breaks a number of tests, which will be addressed in follow-up commits: - The `{tcp,udp}-socket.bind` implementation in `wasmtime-wasi` is implemented using `Linker::func_wrap_concurrent` and thus assumed to be async, whereas the WIT interface says they're sync, leading to a type mismatch error at runtime. Alex and I have discussed this and have a general plan to address it. - A number of tests in the tests/component-model submodule that points to the spec repo are failing. Those will presumably be fixed as part of the upcoming spec PR (although some could be due to bugs in this implementation, in which case I'll fix them). - A number of tests in tests/misc_testsuite are failing. I'll address those in a follow-up commit. Signed-off-by: Joel Dice <[email protected]> * call `check_may_leave` before `check_blocking` `check_blocking` needs access to the current task, but that's not set for post-return functions since those should not be calling _any_ imports at all, so first check for that. Signed-off-by: Joel Dice <[email protected]> * fix `misc_testsuite` test regressions This amounts to adding `async` to any exported component functions that might need to block. Signed-off-by: Joel Dice <[email protected]> * simplify code in `ConcurrentState::check_blocking` Signed-off-by: Joel Dice <[email protected]> * make `thread.yield` a no-op in non-blocking contexts Per the proposed spec changes, `thread.yield` should return control to the guest immediately without allowing any other thread to run. Similarly, when an async-lifted export or callback returns `CALLBACK_CODE_YIELD`, we should call the callback again immediately without allowing another thread to run. Signed-off-by: Joel Dice <[email protected]> * fix build when `component-model-async` feature disabled Signed-off-by: Joel Dice <[email protected]> * fix more test regressions Signed-off-by: Joel Dice <[email protected]> * fix more test regressions Note that this temporarily updates the `tests/component-model` submodule to the branch for WebAssembly/component-model#577 until that PR is merged. Signed-off-by: Joel Dice <[email protected]> * tweak `Trap::CannotBlockSyncTask` message This clarifies that such a task cannot block prior to returning. Signed-off-by: Joel Dice <[email protected]> * fix cancel_host_future test Signed-off-by: Joel Dice <[email protected]> * trap sync-lowered, guest->guest async calls in sync tasks I somehow forgot to address this earlier. Thanks to Luke for catching this. Note that this commit doesn't include test coverage, but Luke's forthecoming tests in the `component-model` repo will cover it, and we'll pull that in with the next submodule update. Signed-off-by: Joel Dice <[email protected]> * switch back to `main` branch of `component-model` repo ...and skip or `should_fail` the tests that won't pass until WebAssembly/component-model#578 is merged. Signed-off-by: Joel Dice <[email protected]> * add `trap-if-block-and-sync.wast` We'll remove this again in favor of the upstream version once WebAssembly/component-model#578 has been merged. Signed-off-by: Joel Dice <[email protected]> * address review feedback - Assert that `StoreOpaque::suspend` is not called in a non-blocking context except in specific circumstances - Typecheck async-ness for dynamic host functions - Use type parameter instead of value parameter in `call_host[_dynamic]` Signed-off-by: Joel Dice <[email protected]> * add explanation comments to `check_blocking` calls Signed-off-by: Joel Dice <[email protected]> * fix fuzz test oracle for async functions Signed-off-by: Joel Dice <[email protected]> --------- Signed-off-by: Joel Dice <[email protected]>
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Dec 10, 2025
alexcrichton
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This is a backport of #12043 to the as-of-now-not-yet-released 40.0.0 branch. This PR contains the behavior change of adding
asyncto function types in the component model type system and this backport means we don't have a release whereasyncis in the type system without affecting the runtime semantics.