Implemented DStream.foreachRDD in the Python API using Py4J callback server.

Author: tdas

examples/src/main/python/streaming/network_wordcount.py

@@ -17,9 +17,7 @@
     fm_lines = lines.flatMap(lambda x: x.split(" "))
     mapped_lines = fm_lines.map(lambda x: (x, 1))
     reduced_lines = mapped_lines.reduceByKey(add)
-    
-    fm_lines.pyprint()
-    mapped_lines.pyprint()
+
     reduced_lines.pyprint()
     ssc.start()
     ssc.awaitTermination()

python/pyspark/java_gateway.py

@@ -102,7 +102,7 @@ def run(self):
         EchoOutputThread(proc.stdout).start()
 
     # Connect to the gateway
-    gateway = JavaGateway(GatewayClient(port=gateway_port), auto_convert=False)
+    gateway = JavaGateway(GatewayClient(port=gateway_port), auto_convert=False, start_callback_server=True)
 
     # Import the classes used by PySpark
     java_import(gateway.jvm, "org.apache.spark.SparkConf")

python/pyspark/streaming/dstream.py

@@ -43,14 +43,6 @@ def print_(self):
         #hack to call print function in DStream
         getattr(self._jdstream, "print")()
 
-    def pyprint(self):
-        """
-        Print the first ten elements of each RDD generated in this DStream. This is an output
-        operator, so this DStream will be registered as an output stream and there materialized.
-
-        """
-        self._jdstream.pyprint()
-
     def filter(self, f):
         """
         Return DStream containing only the elements that satisfy predicate.
@@ -203,6 +195,38 @@ def getNumPartitions(self):
         return 2
 >>>>>>> clean up code
 
+    def foreachRDD(self, func):
+        """
+        """
+        from utils import RDDFunction
+        wrapped_func = RDDFunction(self.ctx, self._jrdd_deserializer, func)
+        self.ctx._jvm.PythonForeachDStream(self._jdstream.dstream(), wrapped_func)
+
+    def pyprint(self):
+        """
+        Print the first ten elements of each RDD generated in this DStream. This is an output
+        operator, so this DStream will be registered as an output stream and there materialized.
+
+        """
+        def takeAndPrint(rdd, time):
+            taken = rdd.take(11)
+            print "-------------------------------------------"
+            print "Time: %s" % (str(time))
+            print "-------------------------------------------"
+            for record in taken[:10]:
+                print record
+            if len(taken) > 10:
+                print "..."
+            print
+
+        self.foreachRDD(takeAndPrint)
+
+
+    #def transform(self, func):
+    #    from utils import RDDFunction
+    #    wrapped_func = RDDFunction(self.ctx, self._jrdd_deserializer, func)
+    #    jdstream = self.ctx._jvm.PythonTransformedDStream(self._jdstream.dstream(), wrapped_func).toJavaDStream
+    #    return DStream(jdstream, self._ssc, ...)  ## DO NOT KNOW HOW 
 
 class PipelinedDStream(DStream):
     def __init__(self, prev, func, preservesPartitioning=False):
@@ -222,7 +246,6 @@ def pipeline_func(split, iterator):
             self._prev_jdstream = prev._prev_jdstream  # maintain the pipeline
             self._prev_jrdd_deserializer = prev._prev_jrdd_deserializer
         self.is_cached = False
-        self.is_checkpointed = False
         self._ssc = prev._ssc
         self.ctx = prev.ctx
         self.prev = prev
@@ -259,4 +282,5 @@ def _jdstream(self):
         return self._jdstream_val
 
     def _is_pipelinable(self):
-        return not (self.is_cached or self.is_checkpointed)
+        return not (self.is_cached)
+

python/pyspark/streaming/utils.py

@@ -15,6 +15,27 @@
 # limitations under the License.
 #
 
+from pyspark.rdd import RDD
+
+class RDDFunction():
+    def __init__(self, ctx, jrdd_deserializer, func):
+        self.ctx = ctx
+        self.deserializer = jrdd_deserializer
+        self.func = func
+
+    def call(self, jrdd, time):
+        # Wrap JavaRDD into python's RDD class
+        rdd = RDD(jrdd, self.ctx, self.deserializer)
+        # Call user defined RDD function
+        self.func(rdd, time)
+
+    def __str__(self):
+        return "%s, %s" % (str(self.deserializer), str(self.func))
+
+    class Java:
+        implements = ['org.apache.spark.streaming.api.python.PythonRDDFunction']
+
+
 
 def msDurationToString(ms):
     """

streaming/src/main/scala/org/apache/spark/streaming/api/java/JavaDStreamLike.scala

@@ -54,14 +54,6 @@ trait JavaDStreamLike[T, This <: JavaDStreamLike[T, This, R], R <: JavaRDDLike[T
     dstream.print()
   }
 
-  /**
-   * Print the first ten elements of each PythonRDD generated in the PythonDStream. This is an output
-   * operator, so this PythonDStream will be registered as an output stream and there materialized.
-   * This function is for PythonAPI.
-   */
-  //TODO move this function to PythonDStream
-  def pyprint() = dstream.pyprint()
-
   /**
    * Return a new DStream in which each RDD has a single element generated by counting each RDD
    * of this DStream.

streaming/src/main/scala/org/apache/spark/streaming/api/python/PythonDStream.scala

@@ -56,6 +56,10 @@ class PythonDStream[T: ClassTag](
     }
   }
 
+  def foreachRDD(foreachFunc: PythonRDDFunction) {
+    new PythonForeachDStream(this, context.sparkContext.clean(foreachFunc, false)).register()
+  }
+
   val asJavaDStream  = JavaDStream.fromDStream(this)
 
   /**
@@ -160,6 +164,40 @@ DStream[Array[Byte]](prev.ssc){
       case None => None
     }
   }
+
+  val asJavaDStream  = JavaDStream.fromDStream(this)
+}
+
+class PythonForeachDStream(
+    prev: DStream[Array[Byte]],
+    foreachFunction: PythonRDDFunction
+  ) extends ForEachDStream[Array[Byte]](
+    prev,
+    (rdd: RDD[Array[Byte]], time: Time) => {
+      foreachFunction.call(rdd.toJavaRDD(), time.milliseconds)
+    }
+  ) {
+
+  this.register()
+}
+/*
+This does not work. Ignore this for now. -TD
+class PythonTransformedDStream(
+    prev: DStream[Array[Byte]],
+    transformFunction: PythonRDDFunction
+  ) extends DStream[Array[Byte]](prev.ssc) {
+
+  override def dependencies = List(prev)
+
+  override def slideDuration: Duration = prev.slideDuration
+
+  override def compute(validTime: Time): Option[RDD[Array[Byte]]] = {
+    prev.getOrCompute(validTime).map(rdd => {
+      transformFunction.call(rdd.toJavaRDD(), validTime.milliseconds).rdd
+    })
+  }
+
   val asJavaDStream  = JavaDStream.fromDStream(this)
   //val asJavaPairDStream : JavaPairDStream[Long, Array[Byte]]  = JavaPairDStream.fromJavaDStream(this)
 }
+*/

streaming/src/main/scala/org/apache/spark/streaming/dstream/DStream.scala

@@ -623,66 +623,6 @@ abstract class DStream[T: ClassTag] (
     new ForEachDStream(this, context.sparkContext.clean(foreachFunc)).register()
   }
 
-//TODO: move pyprint to PythonDStream and executed by py4j call back function
-  /**
-   * Print the first ten elements of each PythonRDD generated in this PythonDStream. This is an output
-   * operator, so this PythonDStream will be registered as an output stream and there materialized.
-   * Since serialized Python object is readable by Python, pyprint writes out binary data to
-   * temporary file and run python script to deserialized and print the first ten elements
-   *
-   * Currently call python script directly. We should avoid this
-   */
-  private[streaming] def pyprint() {
-    def foreachFunc = (rdd: RDD[T], time: Time) => {
-      val iter = rdd.take(11).iterator
-
-      // Generate a temporary file
-      val prefix = "spark"
-      val suffix = ".tmp"
-      val tempFile = File.createTempFile(prefix, suffix)
-      val tempFileStream = new DataOutputStream(new FileOutputStream(tempFile.getAbsolutePath))
-      // Write out serialized python object to temporary file
-      PythonRDD.writeIteratorToStream(iter, tempFileStream)
-      tempFileStream.close()
-
-      // pythonExec should be passed from python. Move pyprint to PythonDStream
-      val pythonExec = new ProcessBuilder().environment().get("PYSPARK_PYTHON")
-
-      val sparkHome = new ProcessBuilder().environment().get("SPARK_HOME")
-      // Call python script to deserialize and print result in stdout
-      val pb = new ProcessBuilder(pythonExec, sparkHome + "/python/pyspark/streaming/pyprint.py", tempFile.getAbsolutePath)
-      val workerEnv = pb.environment()
-
-      // envVars also should be pass from python
-      val pythonPath = sparkHome + "/python/" + File.pathSeparator + workerEnv.get("PYTHONPATH")
-      workerEnv.put("PYTHONPATH", pythonPath)
-      val worker = pb.start()
-      val is = worker.getInputStream()
-      val isr = new InputStreamReader(is)
-      val br = new BufferedReader(isr)
-
-      println ("-------------------------------------------")
-      println ("Time: " + time)
-      println ("-------------------------------------------")
-
-      // Print values which is from python std out
-      var line = ""
-      breakable {
-        while (true) {
-          line = br.readLine()
-          if (line == null) break()
-          println(line)
-        }
-      }
-      // Delete temporary file
-      tempFile.delete()
-      println()
-
-    }
-    new ForEachDStream(this, context.sparkContext.clean(foreachFunc)).register()
-  }
-
-
   /**
    * Return a new DStream in which each RDD contains all the elements in seen in a
    * sliding window of time over this DStream. The new DStream generates RDDs with