Replace JoinIterator & improve ConcatIterator#5033
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adriaanm merged 1 commit intoscala:2.12.xfrom Mar 30, 2016
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The new `ConcatIterator` requires only one extra lightweight wrapper object (cons cell) to be allocated compared to `JoinIterator`. All additional concatenations are then done in place with one cons cell per appended iterator. Running 1000000 iterations of the following benchmark for LHS recursion: ``` def lhs(n: Int) = (1 to n).foldLeft(Iterator.empty: Iterator[Int])((res, _) => res ++ Iterator(1)).sum ``` On 2.12.x before SI-9623 fix: ``` $ ../scala/build-sbt/quick/bin/scala -J-Xmx1024M -nc concatit.scala 1000000: 555ms 1000000: 344ms 1000000: 397ms 1000000: 309ms 1000000: 290ms 1000000: 283ms 1000000: 282ms 1000000: 281ms 1000000: 290ms 1000000: 279ms ``` With SI-9623 fix: ``` $ ../scala/build-sbt/quick/bin/scala -J-Xmx1024M -nc concatit.scala 1000000: 610ms 1000000: 324ms 1000000: 387ms 1000000: 315ms 1000000: 296ms 1000000: 300ms 1000000: 341ms 1000000: 294ms 1000000: 291ms 1000000: 281ms ``` With this version: ``` $ ../scala/build-sbt/quick/bin/scala -J-Xmx1024M -nc concatit.scala 1000000: 362ms 1000000: 162ms 1000000: 140ms 1000000: 150ms 1000000: 110ms 1000000: 57ms 1000000: 79ms 1000000: 109ms 1000000: 120ms 1000000: 49ms ``` And for RHS recursion: ``` def rhs(n: Int) = (1 to n).foldLeft(Iterator.empty: Iterator[Int])((res, _) => Iterator(1) ++ res).sum ``` On 2.12.x before SI-9623 fix: ``` StackOverflowError ``` With SI-9623 fix: ``` StackOverflowError ``` With this version: ``` $ ../scala/build-sbt/quick/bin/scala -J-Xmx1024M -nc concatit.scala 1000000: 3156ms 1000000: 1536ms 1000000: 1240ms 1000000: 1575ms 1000000: 439ms 1000000: 706ms 1000000: 1043ms 1000000: 1211ms 1000000: 515ms 1000000: 314ms ```
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Since this was reviewed before, and the followup comment regarding nulling was implemented, I'm going to merge this! |
This was referenced Apr 7, 2017
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This is a follow-up to #4937 (the "SI-9623 fix" mentioned below). Review by @Ichoran.
The new
ConcatIteratorrequires only one extra lightweight wrapperobject (cons cell) to be allocated compared to
JoinIterator. Alladditional concatenations are then done in place with one cons cell per
appended iterator.
Running 1000000 iterations of the following benchmark for LHS recursion:
On 2.12.x before SI-9623 fix:
With SI-9623 fix:
With this version:
And for RHS recursion:
On 2.12.x before SI-9623 fix:
With SI-9623 fix:
With this version: