akka/akka-core
Support non-eager cancellation for alsoTo steam combinator
Aperta
#27.618 aperta il 3 set 2019
1 - triagedhelp wantedt:stream
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Descrizione
Consider the following code
val (f1, f2) = Source(1 to 100)
.alsoToMat(Sink.head)(Keep.right)
.toMat(Sink.last)(Keep.both)
.run()
for {
head <- f1
last <- f2
} {
println(s"head: $head , last: $last")
}
This prints
head: 1 , last: 1
It appears that the behaviour of alsoTo and alsoToMat was changed as part of #24423 (a followup of #24291 ). For these cases this seams reasonable. However I commonly use alsoToMat to process one source with multiple sinks. I just found out that a sink such as Sink.head which cancels early can have unexpected effects on the other sinks.
This comment suggests adding an overload. However appearently using wireTap was suggested as an alternative. Unfortunately, wiretap will drop elements on backpressure which is not what I want in my usecase.
Would it make sense to add an overloaded version of alsoTo and alsoToMat which includes an eagerCancel boolean?