title: Multiple SpartContexts run on same JVM
body: <p>I am using spark, and got such an error which stop the whole spark process:</p>
  
  <pre><code>16:01:37.289 [main] WARN  org.apache.spark.SparkContext - Another SparkContext is being 
  constructed (or threw an exception in its constructor).  This may indicate an error, since 
  only one SparkContext may be running in this JVM (see SPARK-2243). The other SparkContext 
  was created at:
  org.apache.spark.api.java.JavaSparkContext.&lt;init&gt;(JavaSparkContext.scala:61)
  </code></pre>
  
  <p>I don't think I have multiple <code>SparkContext</code> running on the same JVM. How to check this? Or force kill the one already running?</p>