Merge pull request #3392 from mpilquist/topic/from-iterator-perf

mpilquist · web-flow · commit ce6392eb6ca4 · 2024-02-19T08:52:45.000-05:00
Fix performance of Stream.from(Blocking)Iterator when using large chunk sizes
diff --git a/core/shared/src/main/scala/fs2/Stream.scala b/core/shared/src/main/scala/fs2/Stream.scala
@@ -3605,7 +3605,7 @@ object Stream extends StreamLowPriority {
 
       def getNextChunk(i: Iterator[A]): F[Option[(Chunk[A], Iterator[A])]] =
         F.suspend(hint) {
-          for (_ <- 1 to chunkSize if i.hasNext) yield i.next()
+          i.take(chunkSize).toVector
         }.map { s =>
           if (s.isEmpty) None else Some((Chunk.from(s), i))
         }

Original file line number	Diff line number	Diff line change
`@@ -3605,7 +3605,7 @@ object Stream extends StreamLowPriority {`
`3605`	`3605`
`3606`	`3606`	`def getNextChunk(i: Iterator[A]): F[Option[(Chunk[A], Iterator[A])]] =`
`3607`	`3607`	`F.suspend(hint) {`
`3608`		`- for (_ <- 1 to chunkSize if i.hasNext) yield i.next()`
	`3608`	`+ i.take(chunkSize).toVector`
`3609`	`3609`	`}.map { s =>`
`3610`	`3610`	`if (s.isEmpty) None else Some((Chunk.from(s), i))`
`3611`	`3611`	`}`