Github user tdas commented on a diff in the pull request:
https://github.com/apache/spark/pull/300#discussion_r11759650
--- Diff:
streaming/src/main/scala/org/apache/spark/streaming/receiver/NetworkReceiver.scala
---
@@ -0,0 +1,209 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.streaming.receiver
+
+import java.nio.ByteBuffer
+
+import scala.collection.mutable.ArrayBuffer
+
+import org.apache.spark.storage.StorageLevel
+
+/**
+ * Abstract class of a receiver that can be run on worker nodes to receive
external data. A
+ * custom receiver can be defined by defining the functions onStart() and
onStop(). onStart()
+ * should define the setup steps necessary to start receiving data,
+ * and onStop() should define the cleanup steps necessary to stop
receiving data. A custom
+ * receiver would look something like this.
+ *
+ * class MyReceiver(storageLevel) extends
NetworkReceiver[String](storageLevel) {
+ * def onStart() {
+ * // Setup stuff (start threads, open sockets, etc.) to start
receiving data.
+ * // Must start new thread to receive data, as onStart() must be
non-blocking.
+ *
+ * // Call store(...) in those threads to store received data into
Spark's memory.
+ *
+ * // Call stop(...), restart() or reportError(...) on any thread
based on how
+ * // different errors should be handled.
+ *
+ * // See corresponding method documentation for more details.
+ * }
+ *
+ * def onStop() {
+ * // Cleanup stuff (stop threads, close sockets, etc.) to stop
receiving data.
+ * }
+ * }
+ */
+abstract class NetworkReceiver[T](val storageLevel: StorageLevel) extends
Serializable {
+
+ /**
+ * This method is called by the system when the receiver is started.
This function
+ * must initialize all resources (threads, buffers, etc.) necessary for
receiving data.
+ * This function must be non-blocking, so receiving the data must occur
on a different
+ * thread. Received data can be stored with Spark by calling
`store(data)`.
+ *
+ * If there are errors in threads started here, then following options
can be done
+ * (i) `reportError(...)` can be called to report the error to the
driver.
+ * The receiving of data will continue uninterrupted.
+ * (ii) `stop(...)` can be called to stop receiving data. This will call
`onStop()` to
+ * clear up all resources allocated (threads, buffers, etc.) during
`onStart()`.
+ * (iii) `restart(...)` can be called to restart the receiver. This will
call `onStop()`
+ * immediately, and then `onStart()` after a delay.
+ */
+ def onStart()
+
+ /**
+ * This method is called by the system when the receiver is stopped. All
resources
+ * (threads, buffers, etc.) setup in `onStart()` must be cleaned up in
this method.
+ */
+ def onStop()
+
+ /** Override this to specify a preferred location (hostname). */
+ def preferredLocation : Option[String] = None
+
+ /** Store a single item of received data to Spark's memory. */
+ def store(dataItem: T) {
--- End diff --
Not sure if these are that critical. I would think that if some one is
doing something advanced enough to require overriding them, then they would
know what they are doing.
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