SI-9043 ArrayBuffer.insert and insertAll are very slow

insert and insertAll were slower than their java equivalents by factors
of 5 and 10 respectively.

Benchmark code was provided here:
https://gist.github.com/rklaehn/3e9290118fcf63d1feae

We are using a toList to the source Traversable
Then doing a length and a copy on that collection.

By using an array, we can make use of faster methods.
Managed to get the ratios down to 1.5 and 1.5 respectively.

In addition to this, I think we should consider breaking insert into 2
separate methods, one for a single item and one for a collection.  The
varags version is very expensive when a single item is being inserted.

@phaller @axel22

1 files changed, 36 insertions, 0 deletions

diff --git a/test/junit/scala/collection/mutable/ArrayBufferTest.scala b/test/junit/scala/collection/mutable/ArrayBufferTest.scala
new file mode 100644
index 0000000000..8c83164027
--- /dev/null
+++ b/test/junit/scala/collection/mutable/ArrayBufferTest.scala
@@ -0,0 +1,36 @@
+package scala.collection.mutable
+
+import org.junit.runner.RunWith
+import org.junit.runners.JUnit4
+import org.junit.{Assert, Test}
+
+import scala.tools.testing.AssertUtil
+
+/* Test for SI-9043 */
+@RunWith(classOf[JUnit4])
+class ArrayBufferTest {
+  @Test
+  def testInsertAll: Unit = {
+    val traver = ArrayBuffer(2, 4, 5, 7)
+    val testSeq = List(1, 3, 6, 9)
+
+    def insertAt(x: Int) = {
+      val clone = traver.clone()
+      clone.insertAll(x, testSeq)
+      clone
+    }
+
+    // Just insert some at position 0
+    Assert.assertEquals(ArrayBuffer(1, 3, 6, 9, 2, 4, 5, 7), insertAt(0))
+
+    // Insert in the middle
+    Assert.assertEquals(ArrayBuffer(2, 4, 1, 3, 6, 9, 5, 7), insertAt(2))
+
+    // No strange last position weirdness
+    Assert.assertEquals(ArrayBuffer(2, 4, 5, 7, 1, 3, 6, 9), insertAt(traver.size))
+
+    // Overflow is caught
+    AssertUtil.assertThrows[IndexOutOfBoundsException] { insertAt(-1) }
+    AssertUtil.assertThrows[IndexOutOfBoundsException] { insertAt(traver.size + 10) }
+  }
+}