SparkContext.scala 源代码学习

package org.apache.spark  //定义spark包

 import scala.language.implicitConversions //导入各类包。。。。
class SparkContext(config: SparkConf) extends Logging with ExecutorAllocationClient { //定义类 SparkContext，传入配置参数SparkConf，继承特质Logging及ExecutorAllocationClient

def this() = this(new SparkConf()) //以下一系列辅助构造器，适应各种参数传入构造
def this(config: SparkConf, preferredNodeLocationData: Map[String, Set[SplitInfo]]) = {
     this(config)
     logWarning("Passing in preferred locations has no effect at all, see SPARK-8949")
   }def this(master: String, appName: String, conf: SparkConf) =
     this(SparkContext.updatedConf(conf, master, appName))
 def this(
       master: String,
       appName: String,
       sparkHome: String = null,
       jars: Seq[String] = Nil,
       environment: Map[String, String] = Map(),
       preferredNodeLocationData: Map[String, Set[SplitInfo]] = Map()) =
   {
     this(SparkContext.updatedConf(new SparkConf(), master, appName, sparkHome, jars, environment))
     if (preferredNodeLocationData.nonEmpty) {
       logWarning("Passing in preferred locations has no effect at all, see SPARK-8949")
     }
   }


   // NOTE: The below constructors could be consolidated using default arguments. Due to
   // Scala bug SI-8479, however, this causes the compile step to fail when generating docs.
   // Until we have a good workaround for that bug the constructors remain broken out.


   /**
    * Alternative constructor that allows setting common Spark properties directly
    *
    * @param master Cluster URL to connect to (e.g. mesos://host:port, spark://host:port, local[4]).
    * @param appName A name for your application, to display on the cluster web UI.
    */
   private[spark] def this(master: String, appName: String) =
     this(master, appName, null, Nil, Map())


   /**
    * Alternative constructor that allows setting common Spark properties directly
    *
    * @param master Cluster URL to connect to (e.g. mesos://host:port, spark://host:port, local[4]).
    * @param appName A name for your application, to display on the cluster web UI.
    * @param sparkHome Location where Spark is installed on cluster nodes.
    */
   private[spark] def this(master: String, appName: String, sparkHome: String) =
     this(master, appName, sparkHome, Nil, Map())


   /**
    * Alternative constructor that allows setting common Spark properties directly
    *
    * @param master Cluster URL to connect to (e.g. mesos://host:port, spark://host:port, local[4]).
    * @param appName A name for your application, to display on the cluster web UI.
    * @param sparkHome Location where Spark is installed on cluster nodes.
    * @param jars Collection of JARs to send to the cluster. These can be paths on the local file
    *             system or HDFS, HTTP, HTTPS, or FTP URLs.
    */
   private[spark] def this(master: String, appName: String, sparkHome: String, jars: Seq[String]) =
     this(master, appName, sparkHome, jars, Map())