[SPARK-986]: Job cancelation for PySpark

* Additions to the PySpark API to cancel jobs
* Monitor Thread in PythonRDD to kill Python workers if a task is interrupted

Author: Ahir Reddy <ahirreddy@gmail.com>

Closes #541 from ahirreddy/python-cancel and squashes the following commits:

dfdf447 [Ahir Reddy] Changed success -> completed and made logging message clearer
6c860ab [Ahir Reddy] PR Comments
4b4100a [Ahir Reddy] Success flag
adba6ed [Ahir Reddy] Destroy python workers
27a2f8f [Ahir Reddy] Start the writer thread...
d422f7b [Ahir Reddy] Remove unnecesssary vals
adda337 [Ahir Reddy] Busy wait on the ocntext.interrupted flag, and then kill the python worker
d9e472f [Ahir Reddy] Revert "removed unnecessary vals"
5b9cae5 [Ahir Reddy] removed unnecessary vals
07b54d9 [Ahir Reddy] Fix canceling unit test
8ae9681 [Ahir Reddy] Don't interrupt worker
7722342 [Ahir Reddy] Monitor Thread for python workers
db04e16 [Ahir Reddy] Added canceling api to PySpark

1 files changed, 49 insertions, 3 deletions

diff --git a/python/pyspark/context.py b/python/pyspark/context.py
index f63cc4a55f..c74dc5fd4f 100644
--- a/python/pyspark/context.py
+++ b/python/pyspark/context.py
@@ -429,7 +429,7 @@ class SparkContext(object):
                                storageLevel.deserialized,
                                storageLevel.replication)
 
-    def setJobGroup(self, groupId, description):
+    def setJobGroup(self, groupId, description, interruptOnCancel=False):
         """
         Assigns a group ID to all the jobs started by this thread until the group ID is set to a
         different value or cleared.
@@ -437,8 +437,41 @@ class SparkContext(object):
         Often, a unit of execution in an application consists of multiple Spark actions or jobs.
         Application programmers can use this method to group all those jobs together and give a
         group description. Once set, the Spark web UI will associate such jobs with this group.
-        """
-        self._jsc.setJobGroup(groupId, description)
+
+        The application can use L{SparkContext.cancelJobGroup} to cancel all
+        running jobs in this group.
+
+        >>> import thread, threading
+        >>> from time import sleep
+        >>> result = "Not Set"
+        >>> lock = threading.Lock()
+        >>> def map_func(x):
+        ...     sleep(100)
+        ...     return x * x
+        >>> def start_job(x):
+        ...     global result
+        ...     try:
+        ...         sc.setJobGroup("job_to_cancel", "some description")
+        ...         result = sc.parallelize(range(x)).map(map_func).collect()
+        ...     except Exception as e:
+        ...         result = "Cancelled"
+        ...     lock.release()
+        >>> def stop_job():
+        ...     sleep(5)
+        ...     sc.cancelJobGroup("job_to_cancel")
+        >>> supress = lock.acquire()
+        >>> supress = thread.start_new_thread(start_job, (10,))
+        >>> supress = thread.start_new_thread(stop_job, tuple())
+        >>> supress = lock.acquire()
+        >>> print result
+        Cancelled
+
+        If interruptOnCancel is set to true for the job group, then job cancellation will result
+        in Thread.interrupt() being called on the job's executor threads. This is useful to help ensure
+        that the tasks are actually stopped in a timely manner, but is off by default due to HDFS-1208,
+        where HDFS may respond to Thread.interrupt() by marking nodes as dead.
+        """
+        self._jsc.setJobGroup(groupId, description, interruptOnCancel)
 
     def setLocalProperty(self, key, value):
         """
@@ -460,6 +493,19 @@ class SparkContext(object):
         """
         return self._jsc.sc().sparkUser()
 
+    def cancelJobGroup(self, groupId):
+        """
+        Cancel active jobs for the specified group. See L{SparkContext.setJobGroup}
+        for more information.
+        """
+        self._jsc.sc().cancelJobGroup(groupId)
+
+    def cancelAllJobs(self):
+        """
+        Cancel all jobs that have been scheduled or are running.
+        """
+        self._jsc.sc().cancelAllJobs()
+
 def _test():
     import atexit
     import doctest