diff options
author | Stefan Zeiger <szeiger@novocode.com> | 2016-01-29 17:28:16 +0100 |
---|---|---|
committer | Stefan Zeiger <szeiger@novocode.com> | 2016-02-01 14:41:17 +0100 |
commit | ecee7b75328ae1f856b5fa832ebad7fc9e42f64a (patch) | |
tree | d49c0a1e1d2f1b546d374e8888b431f0e069bf86 /test | |
parent | ea154faf467ae27c221ba0dcd7235e1e55673c51 (diff) | |
download | scala-ecee7b75328ae1f856b5fa832ebad7fc9e42f64a.tar.gz scala-ecee7b75328ae1f856b5fa832ebad7fc9e42f64a.tar.bz2 scala-ecee7b75328ae1f856b5fa832ebad7fc9e42f64a.zip |
SI-9623 Avoid unnecessary hasNext calls in JoinIterator & ConcatIterator
These iterator implementations are used to concatenate two (JoinIterator)
or more (ConcatIterator) other iterators with `++`. They used to perform
many unnecessary calls to the child iterators’ `hasNext` methods.
This improved state machine-based implementation reduces that number to
the bare minimum, i.e. iterating over concatenated iterators with
`foreach` calls the children's `hasNext` methods a total of (number of
children) + (number of elements) times, the same as when iterating over
all children separately.
Diffstat (limited to 'test')
-rw-r--r-- | test/junit/scala/collection/IteratorTest.scala | 28 |
1 files changed, 28 insertions, 0 deletions
diff --git a/test/junit/scala/collection/IteratorTest.scala b/test/junit/scala/collection/IteratorTest.scala index 1c1e50aed9..329c85127a 100644 --- a/test/junit/scala/collection/IteratorTest.scala +++ b/test/junit/scala/collection/IteratorTest.scala @@ -164,4 +164,32 @@ class IteratorTest { assertEquals(1, y.next) assertFalse(x.hasNext) // was true, after advancing underlying iterator } + // SI-9623 + @Test def noExcessiveHasNextInJoinIterator: Unit = { + var counter = 0 + val exp = List(1,2,3,1,2,3) + def it: Iterator[Int] = new Iterator[Int] { + val parent = List(1,2,3).iterator + def next(): Int = parent.next + def hasNext: Boolean = { counter += 1; parent.hasNext } + } + // Iterate separately + val res = new mutable.ArrayBuffer[Int] + it.foreach(res += _) + it.foreach(res += _) + assertSameElements(exp, res) + assertEquals(8, counter) + // JoinIterator + counter = 0 + res.clear + (it ++ it).foreach(res += _) + assertSameElements(exp, res) + assertEquals(8, counter) // was 17 + // ConcatIterator + counter = 0 + res.clear + (Iterator.empty ++ it ++ it).foreach(res += _) + assertSameElements(exp, res) + assertEquals(8, counter) // was 14 + } } |