[SPARK-4415] [PySpark] JVM should exit after Python exit

When JVM is started in a Python process, it should exit once the stdin is closed.

test: add spark.driver.memory in conf/spark-defaults.conf

```
daviesdm:~/work/spark$ cat conf/spark-defaults.conf
spark.driver.memory       8g
daviesdm:~/work/spark$ bin/pyspark
>>> quit
daviesdm:~/work/spark$ jps
4931 Jps
286
daviesdm:~/work/spark$ python wc.py
943738
0.719928026199
daviesdm:~/work/spark$ jps
286
4990 Jps
```

Author: Davies Liu <davies@databricks.com>

Closes #3274 from davies/exit and squashes the following commits:

df0e524 [Davies Liu] address comments
ce8599c [Davies Liu] address comments
050651f [Davies Liu] JVM should exit after Python exit

1 files changed, 3 insertions, 1 deletions

diff --git a/python/pyspark/java_gateway.py b/python/pyspark/java_gateway.py
index 9c70fa5c16..a975dc19cb 100644
--- a/python/pyspark/java_gateway.py
+++ b/python/pyspark/java_gateway.py
@@ -45,7 +45,9 @@ def launch_gateway():
             # Don't send ctrl-c / SIGINT to the Java gateway:
             def preexec_func():
                 signal.signal(signal.SIGINT, signal.SIG_IGN)
-            proc = Popen(command, stdout=PIPE, stdin=PIPE, preexec_fn=preexec_func)
+            env = dict(os.environ)
+            env["IS_SUBPROCESS"] = "1"  # tell JVM to exit after python exits
+            proc = Popen(command, stdout=PIPE, stdin=PIPE, preexec_fn=preexec_func, env=env)
         else:
             # preexec_fn not supported on Windows
             proc = Popen(command, stdout=PIPE, stdin=PIPE)