Github user andrewor14 commented on a diff in the pull request:
https://github.com/apache/spark/pull/5096#discussion_r27764985
--- Diff: core/src/main/scala/org/apache/spark/api/r/RBackend.scala ---
@@ -0,0 +1,145 @@
+/*
+ * 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.api.r
+
+import java.io.{DataOutputStream, File, FileOutputStream, IOException}
+import java.net.{InetSocketAddress, ServerSocket}
+import java.util.concurrent.TimeUnit
+
+import io.netty.bootstrap.ServerBootstrap
+import io.netty.channel.{ChannelFuture, ChannelInitializer, EventLoopGroup}
+import io.netty.channel.nio.NioEventLoopGroup
+import io.netty.channel.socket.SocketChannel
+import io.netty.channel.socket.nio.NioServerSocketChannel
+import io.netty.handler.codec.LengthFieldBasedFrameDecoder
+import io.netty.handler.codec.bytes.{ByteArrayDecoder, ByteArrayEncoder}
+
+import org.apache.spark.Logging
+
+/**
+ * Netty-based backend server that is used to communicate between R and
Java.
+ */
+private[spark] class RBackend {
+
+ private[this] var channelFuture: ChannelFuture = null
+ private[this] var bootstrap: ServerBootstrap = null
+ private[this] var bossGroup: EventLoopGroup = null
+
+ def init(): Int = {
+ bossGroup = new NioEventLoopGroup(2)
+ val workerGroup = bossGroup
+ val handler = new RBackendHandler(this)
+
+ bootstrap = new ServerBootstrap()
+ .group(bossGroup, workerGroup)
+ .channel(classOf[NioServerSocketChannel])
+
+ bootstrap.childHandler(new ChannelInitializer[SocketChannel]() {
+ def initChannel(ch: SocketChannel) = {
+ ch.pipeline()
+ .addLast("encoder", new ByteArrayEncoder())
+ .addLast("frameDecoder",
+ // maxFrameLength = 2G
+ // lengthFieldOffset = 0
+ // lengthFieldLength = 4
+ // lengthAdjustment = 0
+ // initialBytesToStrip = 4, i.e. strip out the length field
itself
+ new LengthFieldBasedFrameDecoder(Integer.MAX_VALUE, 0, 4, 0,
4))
+ .addLast("decoder", new ByteArrayDecoder())
+ .addLast("handler", handler)
+ }
+ })
+
+ channelFuture = bootstrap.bind(new InetSocketAddress(0))
+ channelFuture.syncUninterruptibly()
+
channelFuture.channel().localAddress().asInstanceOf[InetSocketAddress].getPort()
+ }
+
+ def run(): Unit = {
+ channelFuture.channel.closeFuture().syncUninterruptibly()
+ }
+
+ def close(): Unit = {
+ if (channelFuture != null) {
+ // close is a local operation and should finish within milliseconds;
timeout just to be safe
+ channelFuture.channel().close().awaitUninterruptibly(10,
TimeUnit.SECONDS)
+ channelFuture = null
+ }
+ if (bootstrap != null && bootstrap.group() != null) {
+ bootstrap.group().shutdownGracefully()
+ }
+ if (bootstrap != null && bootstrap.childGroup() != null) {
+ bootstrap.childGroup().shutdownGracefully()
+ }
+ bootstrap = null
+ }
+
+}
+
+private[spark] object RBackend extends Logging {
+ def main(args: Array[String]) {
+ if (args.length < 1) {
+ System.err.println("Usage: RBackend <tempFilePath>")
+ System.exit(-1)
+ }
+ val sparkRBackend = new RBackend()
+ try {
+ // bind to random port
+ val boundPort = sparkRBackend.init()
+ val serverSocket = new ServerSocket(0, 1)
+ val listenPort = serverSocket.getLocalPort()
+
+ // tell the R process via temporary file
+ val path = args(0)
+ val f = new File(path + ".tmp")
+ val dos = new DataOutputStream(new FileOutputStream(f))
+ dos.writeInt(boundPort)
+ dos.writeInt(listenPort)
+ dos.close()
+ f.renameTo(new File(path))
+
+ // wait for the end of stdin, then exit
+ new Thread("wait for socket to close") {
+ setDaemon(true)
+ override def run(): Unit = {
+ // any un-catched exception will also shutdown JVM
+ val buf = new Array[Byte](1024)
+ // shutdown JVM if R does not connect back in 10 seconds
+ serverSocket.setSoTimeout(10000)
+ try {
+ val inSocket = serverSocket.accept()
+ serverSocket.close()
+ // wait for the end of socket, closed if R process die
+ inSocket.getInputStream().read(buf)
+ } finally {
+ sparkRBackend.close()
+ System.exit(0)
+ }
+ }
+ }.start()
+
+ sparkRBackend.run()
+ } catch {
+ case e: IOException =>
+ logError("Server shutting down: failed with exception ", e)
+ sparkRBackend.close()
+ System.exit(1)
+ }
+ System.exit(0)
--- End diff --
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