Merge pull request #779 from adatao/adatao-global-SparkEnv

[HOTFIX] Extend thread safety for SparkEnv.get()

core/src/main/scala/spark/SparkEnv.scala

@@ -97,13 +97,26 @@ class SparkEnv (
 
 object SparkEnv extends Logging {
   private val env = new ThreadLocal[SparkEnv]
+  @volatile private var lastSetSparkEnv : SparkEnv = _
 
   def set(e: SparkEnv) {
+	  lastSetSparkEnv = e
     env.set(e)
   }
 
+  /**
+   * Returns the ThreadLocal SparkEnv, if non-null. Else returns the SparkEnv
+   * previously set in any thread.
+   */
   def get: SparkEnv = {
-    env.get()
+    Option(env.get()).getOrElse(lastSetSparkEnv)
+  }
+
+  /**
+   * Returns the ThreadLocal SparkEnv.
+   */
+  def getThreadLocal : SparkEnv = {
+	  env.get()
   }
 
   def createFromSystemProperties(