public static SparkContext create(final SparkConf sparkConf) {
        if (isContextNullOrStopped()) {
            // Set the default app name if it is not specified
            if (sparkConf.get("spark.app.name", DEFAULT_APP_NAME).equals(DEFAULT_APP_NAME)) {
                sparkConf.setAppName(DEFAULT_APP_NAME);
            }
            CONTEXT = SparkContext.getOrCreate(sparkConf);
        }
        return CONTEXT;
    }
This is a static cache the prevents Spark from garbage collecting unreferenced RDDs.

@author Marko A. Rodriguez (http://markorodriguez.com)
spark-gremlin/src/main/java/org/apache/tinkerpop/gremlin/spark/structure/Spark.java