SPARK-5425: Use synchronised methods in system properties to create SparkConf

SPARK-5425: Fixed usages of system properties

This patch fixes few problems caused by the fact that the Scala wrapper over system properties is not thread-safe and is basically invalid because it doesn't take into account the default values which could have been set in the properties object. The problem is fixed by modifying `Utils.getSystemProperties` method so that it uses `stringPropertyNames` method of the `Properties` class, which is thread-safe (internally it creates a defensive copy in a synchronized method) and returns keys of the properties which were set explicitly and which are defined as defaults.
The other related problem, which is fixed here. was in `ResetSystemProperties` mix-in. It created a copy of the system properties in the wrong way.

This patch also introduces a test case for thread-safeness of SparkConf creation.

Refer to the discussion in https://github.com/apache/spark/pull/4220 for more details.

Author: Jacek Lewandowski <lewandowski.jacek@gmail.com>

Closes #4221 from jacek-lewandowski/SPARK-5425-1.2 and squashes the following commits:

87951a2 [Jacek Lewandowski] SPARK-5425: Modified Utils.getSystemProperties to return a map of all system properties - explicit + defaults
01dd5cb [Jacek Lewandowski] SPARK-5425: Use SerializationUtils to save properties in ResetSystemProperties trait
94aeacf [Jacek Lewandowski] SPARK-5425: Use synchronised methods in system properties to create SparkConf

1 files changed, 3 insertions, 1 deletions

diff --git a/examples/src/main/scala/org/apache/spark/examples/DriverSubmissionTest.scala b/examples/src/main/scala/org/apache/spark/examples/DriverSubmissionTest.scala
index 65251e9319..e757283823 100644
--- a/examples/src/main/scala/org/apache/spark/examples/DriverSubmissionTest.scala
+++ b/examples/src/main/scala/org/apache/spark/examples/DriverSubmissionTest.scala
@@ -19,6 +19,8 @@ package org.apache.spark.examples
 
 import scala.collection.JavaConversions._
 
+import org.apache.spark.util.Utils
+
 /** Prints out environmental information, sleeps, and then exits. Made to
   * test driver submission in the standalone scheduler. */
 object DriverSubmissionTest {
@@ -30,7 +32,7 @@ object DriverSubmissionTest {
     val numSecondsToSleep = args(0).toInt
 
     val env = System.getenv()
-    val properties = System.getProperties()
+    val properties = Utils.getSystemProperties
 
     println("Environment variables containing SPARK_TEST:")
     env.filter{case (k, v) => k.contains("SPARK_TEST")}.foreach(println)