[SPARK-15528][SQL] Fix race condition in NumberConverter

## What changes were proposed in this pull request?
A local variable in NumberConverter is wrongly shared between threads.
This pr fixes the race condition.

## How was this patch tested?
Manually checked.

Author: Takeshi YAMAMURO <linguin.m.s@gmail.com>

Closes apache#13391 from maropu/SPARK-15528.

Author: maropu

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/NumberConverter.scala

@@ -21,8 +21,6 @@ import org.apache.spark.unsafe.types.UTF8String
 
 object NumberConverter {
 
-  private val value = new Array[Byte](64)
-
   /**
    * Divide x by m as if x is an unsigned 64-bit integer. Examples:
    * unsignedLongDiv(-1, 2) == Long.MAX_VALUE unsignedLongDiv(6, 3) == 2
@@ -49,7 +47,7 @@ object NumberConverter {
    * @param v is treated as an unsigned 64-bit integer
    * @param radix must be between MIN_RADIX and MAX_RADIX
    */
-  private def decode(v: Long, radix: Int): Unit = {
+  private def decode(v: Long, radix: Int, value: Array[Byte]): Unit = {
     var tmpV = v
     java.util.Arrays.fill(value, 0.asInstanceOf[Byte])
     var i = value.length - 1
@@ -69,11 +67,9 @@ object NumberConverter {
    * @param fromPos is the first element that should be considered
    * @return the result should be treated as an unsigned 64-bit integer.
    */
-  private def encode(radix: Int, fromPos: Int): Long = {
+  private def encode(radix: Int, fromPos: Int, value: Array[Byte]): Long = {
     var v: Long = 0L
     val bound = unsignedLongDiv(-1 - radix, radix) // Possible overflow once
-    // val
-    // exceeds this value
     var i = fromPos
     while (i < value.length && value(i) >= 0) {
       if (v >= bound) {
@@ -94,7 +90,7 @@ object NumberConverter {
    * @param radix must be between MIN_RADIX and MAX_RADIX
    * @param fromPos is the first nonzero element
    */
-  private def byte2char(radix: Int, fromPos: Int): Unit = {
+  private def byte2char(radix: Int, fromPos: Int, value: Array[Byte]): Unit = {
     var i = fromPos
     while (i < value.length) {
       value(i) = Character.toUpperCase(Character.forDigit(value(i), radix)).asInstanceOf[Byte]
@@ -109,9 +105,9 @@ object NumberConverter {
    * @param radix must be between MIN_RADIX and MAX_RADIX
    * @param fromPos is the first nonzero element
    */
-  private def char2byte(radix: Int, fromPos: Int): Unit = {
+  private def char2byte(radix: Int, fromPos: Int, value: Array[Byte]): Unit = {
     var i = fromPos
-    while ( i < value.length) {
+    while (i < value.length) {
       value(i) = Character.digit(value(i), radix).asInstanceOf[Byte]
       i += 1
     }
@@ -124,8 +120,8 @@ object NumberConverter {
    */
   def convert(n: Array[Byte], fromBase: Int, toBase: Int ): UTF8String = {
     if (fromBase < Character.MIN_RADIX || fromBase > Character.MAX_RADIX
-      || Math.abs(toBase) < Character.MIN_RADIX
-      || Math.abs(toBase) > Character.MAX_RADIX) {
+        || Math.abs(toBase) < Character.MIN_RADIX
+        || Math.abs(toBase) > Character.MAX_RADIX) {
       return null
     }
 
@@ -136,15 +132,16 @@ object NumberConverter {
     var (negative, first) = if (n(0) == '-') (true, 1) else (false, 0)
 
     // Copy the digits in the right side of the array
+    val temp = new Array[Byte](64)
     var i = 1
     while (i <= n.length - first) {
-      value(value.length - i) = n(n.length - i)
+      temp(temp.length - i) = n(n.length - i)
       i += 1
     }
-    char2byte(fromBase, value.length - n.length + first)
+    char2byte(fromBase, temp.length - n.length + first, temp)
 
     // Do the conversion by going through a 64 bit integer
-    var v = encode(fromBase, value.length - n.length + first)
+    var v = encode(fromBase, temp.length - n.length + first, temp)
     if (negative && toBase > 0) {
       if (v < 0) {
         v = -1
@@ -156,21 +153,20 @@ object NumberConverter {
       v = -v
       negative = true
     }
-    decode(v, Math.abs(toBase))
+    decode(v, Math.abs(toBase), temp)
 
     // Find the first non-zero digit or the last digits if all are zero.
     val firstNonZeroPos = {
-      val firstNonZero = value.indexWhere( _ != 0)
-      if (firstNonZero != -1) firstNonZero else value.length - 1
+      val firstNonZero = temp.indexWhere( _ != 0)
+      if (firstNonZero != -1) firstNonZero else temp.length - 1
     }
-
-    byte2char(Math.abs(toBase), firstNonZeroPos)
+    byte2char(Math.abs(toBase), firstNonZeroPos, temp)
 
     var resultStartPos = firstNonZeroPos
     if (negative && toBase < 0) {
       resultStartPos = firstNonZeroPos - 1
-      value(resultStartPos) = '-'
+      temp(resultStartPos) = '-'
     }
-    UTF8String.fromBytes(java.util.Arrays.copyOfRange(value, resultStartPos, value.length))
+    UTF8String.fromBytes(java.util.Arrays.copyOfRange(temp, resultStartPos, temp.length))
   }
 }