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chore: For WASI builds only, use fatalError in all .wait() calls. Recommend using .get() instead. #3421

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chore: For WASI builds only, use fatalError in all .wait() calls. Recommend using .get() instead. #3421

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20 changes: 20 additions & 0 deletions Sources/NIOCore/EventLoopFuture.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -1091,6 +1091,26 @@ extension EventLoopFuture {
@preconcurrency
@inlinable
public func wait(file: StaticString = #file, line: UInt = #line) throws -> Value where Value: Sendable {
#if os(WASI)
// NOTE: As of July 22, 2025 `wait()` calling wait() is not supported on WASI platforms.
//
// This may change down the road if and when true multi-threading evolves. But right now
// calling wait here results in the following runtime crash:
//
// ```
// SomeExecutable.wasm:0x123456 Uncaught (in promise) RuntimeError: Atomics.wait cannot be called in this context
// ```
//
// Using the following fatal error here gives wasm runtime users a much more clear error message
// to identify the issue.
//
// If you're running into this error on WASI, refactoring to `get()` instead of `wait()` will
// likely solve the issue.
fatalError(
"NIO's wait() function should not be called on WASI platforms. It will freeze or crash. Use get() instead."
)
#endif // os(WASI)

try self._blockingWaitForFutureCompletion(file: file, line: line)
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@MaxDesiatov MaxDesiatov Nov 3, 2025 •
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This should fix CI breakage.

Suggested change
try self._blockingWaitForFutureCompletion(file: file, line: line)
return try self._blockingWaitForFutureCompletion(file: file, line: line)

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Hmm, odd that those errors don't show up for me. But could be a linux vs macOS, or swift version difference thing.

https://github.com/apple/swift-nio/actions/runs/18985478598/job/54366370185?pr=3421

But I am seeing some compiler warnings in the wasm build. I don't think adding the return will address that warning. I'll push a slightly different revision that should resolve the warnings as well.

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@MaxDesiatov MaxDesiatov Nov 3, 2025 •
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Are the errors not reproducible with the exact same invocation and container image that CI uses?

docker run -v /home/runner/work/swift-nio/swift-nio:/swift-nio -w /swift-nio \
  -e CI=true -e GITHUB_ACTIONS=true -e SWIFT_VERSION=6.0 \
  -e workspace=/swift-nio swift:6.0-jammy bash

}

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