[SPARK-5064][GraphX] Add numEdges upperbound validation for R-MAT graph generator to prevent infinite loop

I looked into GraphGenerators#chooseCell, and found that chooseCell can't generate more edges than pow(2, (2 * (log2(numVertices)-1))) to make a Power-law graph. (Ex. numVertices:4 upperbound:4, numVertices:8 upperbound:16, numVertices:16 upperbound:64)
If we request more edges over the upperbound, rmatGraph fall into infinite loop. So, how about adding an argument validation?

Author: Kenji Kikushima <kikushima.kenji@lab.ntt.co.jp>

Closes #3950 from kj-ki/SPARK-5064 and squashes the following commits:

4ee18c7 [Ankur Dave] Reword error message and add unit test
d760bc7 [Kenji Kikushima] Add numEdges upperbound validation for R-MAT graph generator to prevent infinite loop.

1 files changed, 6 insertions, 0 deletions

diff --git a/graphx/src/main/scala/org/apache/spark/graphx/util/GraphGenerators.scala b/graphx/src/main/scala/org/apache/spark/graphx/util/GraphGenerators.scala
index 8a13c74221..2d6a825b61 100644
--- a/graphx/src/main/scala/org/apache/spark/graphx/util/GraphGenerators.scala
+++ b/graphx/src/main/scala/org/apache/spark/graphx/util/GraphGenerators.scala
@@ -133,6 +133,12 @@ object GraphGenerators {
     // This ensures that the 4 quadrants are the same size at all recursion levels
     val numVertices = math.round(
       math.pow(2.0, math.ceil(math.log(requestedNumVertices) / math.log(2.0)))).toInt
+    val numEdgesUpperBound =
+      math.pow(2.0, 2 * ((math.log(numVertices) / math.log(2.0)) - 1)).toInt
+    if (numEdgesUpperBound < numEdges) {
+      throw new IllegalArgumentException(
+        s"numEdges must be <= $numEdgesUpperBound but was $numEdges")
+    }
     var edges: Set[Edge[Int]] = Set()
     while (edges.size < numEdges) {
       if (edges.size % 100 == 0) {