Concurrent iteration of AsyncStream can 'leak' continuations #71412
Description
Description
per its documention, AsyncStream nominally does not support concurrent iteration. in practice, however, this functionality exists and can be used. if one creates multiple iterators over a single underlying AsyncStream and uses them from different Tasks, then termination of the stream may cause some number of the concurrent iterators to remain suspended indefinitely.
Reproduction
func test_multiConsume() async {
let (stream, continuation) = AsyncStream<Int>.makeStream()
await withTaskGroup(of: Void.self) { group in
for i in 1...10 { // fewer consumers will often also result in the same issue
group.addTask {
print("starting iterator \(i)")
for await value in stream {
print("iterator \(i): \(value)")
}
print("iterator \(i) finished")
}
}
group.addTask {
print("terminating stream")
continuation.finish()
}
}
print("done") // generally never reached
}Expected behavior
AsyncStream should not allow concurrent iteration. attempting to do so should be either a compiler or runtime error, as it (sometimes) is with AsyncThrowingStream.
Environment
swift-driver version: 1.87.3 Apple Swift version 5.9.2 (swiftlang-5.9.2.2.56 clang-1500.1.0.2.5)
Target: arm64-apple-macosx13.0