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from py4j.java_gateway import java_import, is_instance_of
from pyspark import RDD, SparkConf
from pyspark.serializers import NoOpSerializer, UTF8Deserializer, CloudPickleSerializer
from pyspark.context import SparkContext
from pyspark.storagelevel import StorageLevel
from pyspark.streaming.dstream import DStream
from pyspark.streaming.util import TransformFunction, TransformFunctionSerializer
__all__ = ["StreamingContext"]
[docs]class StreamingContext(object):
"""
Main entry point for Spark Streaming functionality. A StreamingContext
represents the connection to a Spark cluster, and can be used to create
:class:`DStream` various input sources. It can be from an existing :class:`SparkContext`.
After creating and transforming DStreams, the streaming computation can
be started and stopped using `context.start()` and `context.stop()`,
respectively. `context.awaitTermination()` allows the current thread
to wait for the termination of the context by `stop()` or by an exception.
Parameters
----------
sparkContext : :class:`SparkContext`
SparkContext object.
batchDuration : int, optional
the time interval (in seconds) at which streaming
data will be divided into batches
"""
_transformerSerializer = None
# Reference to a currently active StreamingContext
_activeContext = None
def __init__(self, sparkContext, batchDuration=None, jssc=None):
self._sc = sparkContext
self._jvm = self._sc._jvm
self._jssc = jssc or self._initialize_context(self._sc, batchDuration)
def _initialize_context(self, sc, duration):
self._ensure_initialized()
return self._jvm.JavaStreamingContext(sc._jsc, self._jduration(duration))
def _jduration(self, seconds):
"""
Create Duration object given number of seconds
"""
return self._jvm.Duration(int(seconds * 1000))
@classmethod
def _ensure_initialized(cls):
SparkContext._ensure_initialized()
gw = SparkContext._gateway
java_import(gw.jvm, "org.apache.spark.streaming.*")
java_import(gw.jvm, "org.apache.spark.streaming.api.java.*")
java_import(gw.jvm, "org.apache.spark.streaming.api.python.*")
from pyspark.java_gateway import ensure_callback_server_started
ensure_callback_server_started(gw)
# register serializer for TransformFunction
# it happens before creating SparkContext when loading from checkpointing
cls._transformerSerializer = TransformFunctionSerializer(
SparkContext._active_spark_context, CloudPickleSerializer(), gw)
[docs] @classmethod
def getOrCreate(cls, checkpointPath, setupFunc):
"""
Either recreate a StreamingContext from checkpoint data or create a new StreamingContext.
If checkpoint data exists in the provided `checkpointPath`, then StreamingContext will be
recreated from the checkpoint data. If the data does not exist, then the provided setupFunc
will be used to create a new context.
Parameters
----------
checkpointPath : str
Checkpoint directory used in an earlier streaming program
setupFunc : function
Function to create a new context and setup DStreams
"""
cls._ensure_initialized()
gw = SparkContext._gateway
# Check whether valid checkpoint information exists in the given path
ssc_option = gw.jvm.StreamingContextPythonHelper().tryRecoverFromCheckpoint(checkpointPath)
if ssc_option.isEmpty():
ssc = setupFunc()
ssc.checkpoint(checkpointPath)
return ssc
jssc = gw.jvm.JavaStreamingContext(ssc_option.get())
# If there is already an active instance of Python SparkContext use it, or create a new one
if not SparkContext._active_spark_context:
jsc = jssc.sparkContext()
conf = SparkConf(_jconf=jsc.getConf())
SparkContext(conf=conf, gateway=gw, jsc=jsc)
sc = SparkContext._active_spark_context
# update ctx in serializer
cls._transformerSerializer.ctx = sc
return StreamingContext(sc, None, jssc)
[docs] @classmethod
def getActive(cls):
"""
Return either the currently active StreamingContext (i.e., if there is a context started
but not stopped) or None.
"""
activePythonContext = cls._activeContext
if activePythonContext is not None:
# Verify that the current running Java StreamingContext is active and is the same one
# backing the supposedly active Python context
activePythonContextJavaId = activePythonContext._jssc.ssc().hashCode()
activeJvmContextOption = activePythonContext._jvm.StreamingContext.getActive()
if activeJvmContextOption.isEmpty():
cls._activeContext = None
elif activeJvmContextOption.get().hashCode() != activePythonContextJavaId:
cls._activeContext = None
raise RuntimeError(
"JVM's active JavaStreamingContext is not the JavaStreamingContext "
"backing the action Python StreamingContext. This is unexpected.")
return cls._activeContext
[docs] @classmethod
def getActiveOrCreate(cls, checkpointPath, setupFunc):
"""
Either return the active StreamingContext (i.e. currently started but not stopped),
or recreate a StreamingContext from checkpoint data or create a new StreamingContext
using the provided setupFunc function. If the checkpointPath is None or does not contain
valid checkpoint data, then setupFunc will be called to create a new context and setup
DStreams.
Parameters
----------
checkpointPath : str
Checkpoint directory used in an earlier streaming program. Can be
None if the intention is to always create a new context when there
is no active context.
setupFunc : function
Function to create a new JavaStreamingContext and setup DStreams
"""
if not callable(setupFunc):
raise TypeError("setupFunc should be callable.")
activeContext = cls.getActive()
if activeContext is not None:
return activeContext
elif checkpointPath is not None:
return cls.getOrCreate(checkpointPath, setupFunc)
else:
return setupFunc()
@property
def sparkContext(self):
"""
Return SparkContext which is associated with this StreamingContext.
"""
return self._sc
[docs] def start(self):
"""
Start the execution of the streams.
"""
self._jssc.start()
StreamingContext._activeContext = self
[docs] def awaitTermination(self, timeout=None):
"""
Wait for the execution to stop.
Parameters
----------
timeout : int, optional
time to wait in seconds
"""
if timeout is None:
self._jssc.awaitTermination()
else:
self._jssc.awaitTerminationOrTimeout(int(timeout * 1000))
[docs] def awaitTerminationOrTimeout(self, timeout):
"""
Wait for the execution to stop. Return `true` if it's stopped; or
throw the reported error during the execution; or `false` if the
waiting time elapsed before returning from the method.
Parameters
----------
timeout : int
time to wait in seconds
"""
return self._jssc.awaitTerminationOrTimeout(int(timeout * 1000))
[docs] def stop(self, stopSparkContext=True, stopGraceFully=False):
"""
Stop the execution of the streams, with option of ensuring all
received data has been processed.
Parameters
----------
stopSparkContext : bool, optional
Stop the associated SparkContext or not
stopGracefully : bool, optional
Stop gracefully by waiting for the processing of all received
data to be completed
"""
self._jssc.stop(stopSparkContext, stopGraceFully)
StreamingContext._activeContext = None
if stopSparkContext:
self._sc.stop()
[docs] def remember(self, duration):
"""
Set each DStreams in this context to remember RDDs it generated
in the last given duration. DStreams remember RDDs only for a
limited duration of time and releases them for garbage collection.
This method allows the developer to specify how long to remember
the RDDs (if the developer wishes to query old data outside the
DStream computation).
Parameters
----------
duration : int
Minimum duration (in seconds) that each DStream should remember its RDDs
"""
self._jssc.remember(self._jduration(duration))
[docs] def checkpoint(self, directory):
"""
Sets the context to periodically checkpoint the DStream operations for master
fault-tolerance. The graph will be checkpointed every batch interval.
Parameters
----------
directory : str
HDFS-compatible directory where the checkpoint data will be reliably stored
"""
self._jssc.checkpoint(directory)
[docs] def socketTextStream(self, hostname, port, storageLevel=StorageLevel.MEMORY_AND_DISK_2):
"""
Create an input from TCP source hostname:port. Data is received using
a TCP socket and receive byte is interpreted as UTF8 encoded ``\\n`` delimited
lines.
Parameters
----------
hostname : str
Hostname to connect to for receiving data
port : int
Port to connect to for receiving data
storageLevel : :class:`pyspark.StorageLevel`, optional
Storage level to use for storing the received objects
"""
jlevel = self._sc._getJavaStorageLevel(storageLevel)
return DStream(self._jssc.socketTextStream(hostname, port, jlevel), self,
UTF8Deserializer())
[docs] def textFileStream(self, directory):
"""
Create an input stream that monitors a Hadoop-compatible file system
for new files and reads them as text files. Files must be written to the
monitored directory by "moving" them from another location within the same
file system. File names starting with . are ignored.
The text files must be encoded as UTF-8.
"""
return DStream(self._jssc.textFileStream(directory), self, UTF8Deserializer())
[docs] def binaryRecordsStream(self, directory, recordLength):
"""
Create an input stream that monitors a Hadoop-compatible file system
for new files and reads them as flat binary files with records of
fixed length. Files must be written to the monitored directory by "moving"
them from another location within the same file system.
File names starting with . are ignored.
Parameters
----------
directory : str
Directory to load data from
recordLength : int
Length of each record in bytes
"""
return DStream(self._jssc.binaryRecordsStream(directory, recordLength), self,
NoOpSerializer())
def _check_serializers(self, rdds):
# make sure they have same serializer
if len(set(rdd._jrdd_deserializer for rdd in rdds)) > 1:
for i in range(len(rdds)):
# reset them to sc.serializer
rdds[i] = rdds[i]._reserialize()
[docs] def queueStream(self, rdds, oneAtATime=True, default=None):
"""
Create an input stream from a queue of RDDs or list. In each batch,
it will process either one or all of the RDDs returned by the queue.
Parameters
----------
rdds : list
Queue of RDDs
oneAtATime : bool, optional
pick one rdd each time or pick all of them once.
default : :class:`pyspark.RDD`, optional
The default rdd if no more in rdds
Notes
-----
Changes to the queue after the stream is created will not be recognized.
"""
if default and not isinstance(default, RDD):
default = self._sc.parallelize(default)
if not rdds and default:
rdds = [rdds]
if rdds and not isinstance(rdds[0], RDD):
rdds = [self._sc.parallelize(input) for input in rdds]
self._check_serializers(rdds)
queue = self._jvm.PythonDStream.toRDDQueue([r._jrdd for r in rdds])
if default:
default = default._reserialize(rdds[0]._jrdd_deserializer)
jdstream = self._jssc.queueStream(queue, oneAtATime, default._jrdd)
else:
jdstream = self._jssc.queueStream(queue, oneAtATime)
return DStream(jdstream, self, rdds[0]._jrdd_deserializer)
[docs] def transform(self, dstreams, transformFunc):
"""
Create a new DStream in which each RDD is generated by applying
a function on RDDs of the DStreams. The order of the JavaRDDs in
the transform function parameter will be the same as the order
of corresponding DStreams in the list.
"""
jdstreams = [d._jdstream for d in dstreams]
# change the final serializer to sc.serializer
func = TransformFunction(self._sc,
lambda t, *rdds: transformFunc(rdds),
*[d._jrdd_deserializer for d in dstreams])
jfunc = self._jvm.TransformFunction(func)
jdstream = self._jssc.transform(jdstreams, jfunc)
return DStream(jdstream, self, self._sc.serializer)
[docs] def union(self, *dstreams):
"""
Create a unified DStream from multiple DStreams of the same
type and same slide duration.
"""
if not dstreams:
raise ValueError("should have at least one DStream to union")
if len(dstreams) == 1:
return dstreams[0]
if len(set(s._jrdd_deserializer for s in dstreams)) > 1:
raise ValueError("All DStreams should have same serializer")
if len(set(s._slideDuration for s in dstreams)) > 1:
raise ValueError("All DStreams should have same slide duration")
jdstream_cls = SparkContext._jvm.org.apache.spark.streaming.api.java.JavaDStream
jpair_dstream_cls = SparkContext._jvm.org.apache.spark.streaming.api.java.JavaPairDStream
gw = SparkContext._gateway
if is_instance_of(gw, dstreams[0]._jdstream, jdstream_cls):
cls = jdstream_cls
elif is_instance_of(gw, dstreams[0]._jdstream, jpair_dstream_cls):
cls = jpair_dstream_cls
else:
cls_name = dstreams[0]._jdstream.getClass().getCanonicalName()
raise TypeError("Unsupported Java DStream class %s" % cls_name)
jdstreams = gw.new_array(cls, len(dstreams))
for i in range(0, len(dstreams)):
jdstreams[i] = dstreams[i]._jdstream
return DStream(self._jssc.union(jdstreams), self, dstreams[0]._jrdd_deserializer)
[docs] def addStreamingListener(self, streamingListener):
"""
Add a [[org.apache.spark.streaming.scheduler.StreamingListener]] object for
receiving system events related to streaming.
"""
self._jssc.addStreamingListener(self._jvm.JavaStreamingListenerWrapper(
self._jvm.PythonStreamingListenerWrapper(streamingListener)))