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Fix Flow.timeout swallowing the channel closure exception #4072

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merged 1 commit into from
Mar 25, 2024
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Fix Flow.timeout swallowing the channel closure exception #4072

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1 change: 1 addition & 0 deletions kotlinx-coroutines-core/common/src/flow/operators/Delay.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -394,6 +394,7 @@ private fun <T> Flow<T>.timeoutInternal(
value.onSuccess {
downStream.emit(it)
}.onClosed {
it?.let { throw it }
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Is it correct that the reason this issue manifested itself is our fusing optimization?

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Oh, it boils down to the following:

val job = Job()
val produce = produce<Int>(job) { close(TestException()) }
(produce as Job).join()
job.isCancelled // False

Which makes sense for produce specifically (when it's used as a standalone coroutine builder), but not much when used as part of the flow machinery

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Also, kind of confusing semantics-wise: close with a cause fails the channel, and when a coroutine fails, the channel fails as well. Yet the channel failure on its now does not represent failure.

return@onReceiveCatching false
}
return@onReceiveCatching true
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11 changes: 11 additions & 0 deletions kotlinx-coroutines-core/common/test/flow/operators/TimeoutTest.kt
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Expand Up @@ -237,6 +237,17 @@ class TimeoutTest : TestBase() {
testImmediateTimeout(-1.seconds)
}

@Test
fun testClosing() = runTest {
assertFailsWith<TestException> {
channelFlow<Int> { close(TestException()) }
.timeout(Duration.INFINITE)
.collect {
expectUnreached()
}
}
}

private fun testImmediateTimeout(timeout: Duration) {
expect(1)
val flow = emptyFlow<Int>().timeout(timeout)
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