Pyspark的Py4JJavaError None.org.apache.spark.api.java.JavaSparkContext

Question

下面的代码

import findspark
findspark.init()
import pyspark
import random
sc = pyspark.SparkContext(master = "spark://host:7077" ,appName="Pi")
num_samples = 1000
def inside(p):     
  x, y = random.random(), random.random()
  return x*x + y*y < 1
count = sc.parallelize(range(0, num_samples)).filter(inside).count()
pi = 4 * count / num_samples
print(pi)
sc.stop()

错误：

Py4JJavaError: An error occurred while calling None.org.apache.spark.api.java.JavaSparkContext.
: java.lang.NullPointerException
    at org.apache.spark.storage.BlockManagerMaster.registerBlockManager(BlockManagerMaster.scala:64)
    at org.apache.spark.storage.BlockManager.initialize(BlockManager.scala:243)
    at org.apache.spark.SparkContext.<init>(SparkContext.scala:509)
    at org.apache.spark.api.java.JavaSparkContext.<init>(JavaSparkContext.scala:58)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45
Error on line 5