SparkContext

1.创建Spark 执行环境SparkEnv

createSparkEnv方法其实是调用createDriverEnv创建SparkEnv，createDriverEnv方法中，获取Driver相关信息，然后调用了SparkEnv私有的create方法。具体请查看SparkEnv

// Create the Spark execution environment (cache, map output tracker, etc)
_env = createSparkEnv(_conf, isLocal, listenerBus)
SparkEnv.set(_env)

  // This function allows components created by SparkEnv to be mocked in unit tests:
  private[spark] def createSparkEnv(
      conf: SparkConf,
      isLocal: Boolean,
      listenerBus: LiveListenerBus): SparkEnv = {
    SparkEnv.createDriverEnv(conf, isLocal, listenerBus, SparkContext.numDriverCores(master))
  }