add TimedIterator

core/src/main/scala/spark/util/TimedIterator.scala

@@ -0,0 +1,32 @@
+package spark.util
+
+/**
+ * A utility for tracking the total time an iterator takes to iterate through its elements.
+ *
+ * In general, this should only be used if you expect it to take a considerable amount of time
+ * (eg. milliseconds) to get each element -- otherwise, the timing won't be very accurate,
+ * and you are probably just adding more overhead
+ */
+class TimedIterator[+A](val sub: Iterator[A]) extends Iterator[A] {
+  private var netMillis = 0l
+  private var nElems = 0
+  def hasNext = {
+    val start = System.currentTimeMillis()
+    val r = sub.hasNext
+    val end = System.currentTimeMillis()
+    netMillis += (end - start)
+    r
+  }
+  def next = {
+    val start = System.currentTimeMillis()
+    val r = sub.next
+    val end = System.currentTimeMillis()
+    netMillis += (end - start)
+    nElems += 1
+    r
+  }
+
+  def getNetMillis = netMillis
+  def getAverageTimePerItem = netMillis / nElems.toDouble
+
+}