1.x: optimize concatMapIterable/flatMapIterable #3864
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| BackpressureUtils.getAndAddRequest(requested, n); | ||
| drain(); | ||
| } else | ||
| if (n < 0) { |
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Could you move the if on the same line as the else, it makes me uncomfortable to see a line ending with else
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Other that my previous comment, 👍. |
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This PR reduces the overhead of
concatMapIterable/flatMapIterableby not wrapping them intoObservable.fromsources but handling the generatedIterables directly.Since
Iterables are inherently synchronous, there is no difference between the two operators that now use the common underlying operator (i.e., flatMap can't chose a different source because it can't tell if anIterablesource is not ready or not;hasNext()is for indicating completion, not temporary lack of data).Benchmark (i7 4790, Window 7 x64, Java 8u77):
Iterable-Mis the current master,Plainis usingconcatMap(Observable::from)as a reference.The
count=1cases are bit slower because there is no good way of detecting if anIterableholds only a single element, unlike withjust(), and have to instantiate the full infrastructure even for a single element.The same table using the master as baseline: