Utils.scala

/*
 * 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.util

import java.io._
import java.net._
import java.nio.ByteBuffer
import java.util.{Properties, Locale, Random, UUID}
import java.util.concurrent.{ThreadFactory, ConcurrentHashMap, Executors, ThreadPoolExecutor}

import org.eclipse.jetty.util.MultiException

import scala.collection.JavaConversions._
import scala.collection.Map
import scala.collection.mutable.ArrayBuffer
import scala.io.Source
import scala.reflect.ClassTag
import scala.util.Try
import scala.util.control.{ControlThrowable, NonFatal}

import com.google.common.io.Files
import com.google.common.util.concurrent.ThreadFactoryBuilder
import org.apache.commons.lang3.SystemUtils
import org.apache.hadoop.conf.Configuration
import org.apache.log4j.PropertyConfigurator
import org.apache.hadoop.fs.{FileSystem, FileUtil, Path}
import org.json4s._
import tachyon.client.{TachyonFile,TachyonFS}

import org.apache.spark._
import org.apache.spark.executor.ExecutorUncaughtExceptionHandler
import org.apache.spark.serializer.{DeserializationStream, SerializationStream, SerializerInstance}

/** CallSite represents a place in user code. It can have a short and a long form. */
private[spark] case class CallSite(shortForm: String, longForm: String)

private[spark] object CallSite {
  val SHORT_FORM = "callSite.short"
  val LONG_FORM = "callSite.long"
}

/**
 * Various utility methods used by Spark.
 */
private[spark] object Utils extends Logging {
  val random = new Random()

  /** Serialize an object using Java serialization */
  def serialize[T](o: T): Array[Byte] = {
    val bos = new ByteArrayOutputStream()
    val oos = new ObjectOutputStream(bos)
    oos.writeObject(o)
    oos.close()
    bos.toByteArray
  }

  /** Deserialize an object using Java serialization */
  def deserialize[T](bytes: Array[Byte]): T = {
    val bis = new ByteArrayInputStream(bytes)
    val ois = new ObjectInputStream(bis)
    ois.readObject.asInstanceOf[T]
  }

  /** Deserialize an object using Java serialization and the given ClassLoader */
  def deserialize[T](bytes: Array[Byte], loader: ClassLoader): T = {
    val bis = new ByteArrayInputStream(bytes)
    val ois = new ObjectInputStream(bis) {
      override def resolveClass(desc: ObjectStreamClass) =
        Class.forName(desc.getName, false, loader)
    }
    ois.readObject.asInstanceOf[T]
  }

  /** Deserialize a Long value (used for [[org.apache.spark.api.python.PythonPartitioner]]) */
  def deserializeLongValue(bytes: Array[Byte]) : Long = {
    // Note: we assume that we are given a Long value encoded in network (big-endian) byte order
    var result = bytes(7) & 0xFFL
    result = result + ((bytes(6) & 0xFFL) << 8)
    result = result + ((bytes(5) & 0xFFL) << 16)
    result = result + ((bytes(4) & 0xFFL) << 24)
    result = result + ((bytes(3) & 0xFFL) << 32)
    result = result + ((bytes(2) & 0xFFL) << 40)
    result = result + ((bytes(1) & 0xFFL) << 48)
    result + ((bytes(0) & 0xFFL) << 56)
  }

  /** Serialize via nested stream using specific serializer */
  def serializeViaNestedStream(os: OutputStream, ser: SerializerInstance)(
      f: SerializationStream => Unit) = {
    val osWrapper = ser.serializeStream(new OutputStream {
      def write(b: Int) = os.write(b)

      override def write(b: Array[Byte], off: Int, len: Int) = os.write(b, off, len)
    })
    try {
      f(osWrapper)
    } finally {
      osWrapper.close()
    }
  }

  /** Deserialize via nested stream using specific serializer */
  def deserializeViaNestedStream(is: InputStream, ser: SerializerInstance)(
      f: DeserializationStream => Unit) = {
    val isWrapper = ser.deserializeStream(new InputStream {
      def read(): Int = is.read()

      override def read(b: Array[Byte], off: Int, len: Int): Int = is.read(b, off, len)
    })
    try {
      f(isWrapper)
    } finally {
      isWrapper.close()
    }
  }

  /**
   * Get the ClassLoader which loaded Spark.
   */
  def getSparkClassLoader = getClass.getClassLoader

  /**
   * Get the Context ClassLoader on this thread or, if not present, the ClassLoader that
   * loaded Spark.
   *
   * This should be used whenever passing a ClassLoader to Class.ForName or finding the currently
   * active loader when setting up ClassLoader delegation chains.
   */
  def getContextOrSparkClassLoader =
    Option(Thread.currentThread().getContextClassLoader).getOrElse(getSparkClassLoader)

  /** Determines whether the provided class is loadable in the current thread. */
  def classIsLoadable(clazz: String): Boolean = {
    Try { Class.forName(clazz, false, getContextOrSparkClassLoader) }.isSuccess
  }

  /** Preferred alternative to Class.forName(className) */
  def classForName(className: String) = Class.forName(className, true, getContextOrSparkClassLoader)

  /**
   * Primitive often used when writing [[java.nio.ByteBuffer]] to [[java.io.DataOutput]]
   */
  def writeByteBuffer(bb: ByteBuffer, out: ObjectOutput) = {
    if (bb.hasArray) {
      out.write(bb.array(), bb.arrayOffset() + bb.position(), bb.remaining())
    } else {
      val bbval = new Array[Byte](bb.remaining())
      bb.get(bbval)
      out.write(bbval)
    }
  }

  private val shutdownDeletePaths = new scala.collection.mutable.HashSet[String]()
  private val shutdownDeleteTachyonPaths = new scala.collection.mutable.HashSet[String]()

  // Register the path to be deleted via shutdown hook
  def registerShutdownDeleteDir(file: File) {
    val absolutePath = file.getAbsolutePath()
    shutdownDeletePaths.synchronized {
      shutdownDeletePaths += absolutePath
    }
  }

  // Register the tachyon path to be deleted via shutdown hook
  def registerShutdownDeleteDir(tachyonfile: TachyonFile) {
    val absolutePath = tachyonfile.getPath()
    shutdownDeleteTachyonPaths.synchronized {
      shutdownDeleteTachyonPaths += absolutePath
    }
  }

  // Is the path already registered to be deleted via a shutdown hook ?
  def hasShutdownDeleteDir(file: File): Boolean = {
    val absolutePath = file.getAbsolutePath()
    shutdownDeletePaths.synchronized {
      shutdownDeletePaths.contains(absolutePath)
    }
  }

  // Is the path already registered to be deleted via a shutdown hook ?
  def hasShutdownDeleteTachyonDir(file: TachyonFile): Boolean = {
    val absolutePath = file.getPath()
    shutdownDeletePaths.synchronized {
      shutdownDeletePaths.contains(absolutePath)
    }
  }

  // Note: if file is child of some registered path, while not equal to it, then return true;
  // else false. This is to ensure that two shutdown hooks do not try to delete each others
  // paths - resulting in IOException and incomplete cleanup.
  def hasRootAsShutdownDeleteDir(file: File): Boolean = {
    val absolutePath = file.getAbsolutePath()
    val retval = shutdownDeletePaths.synchronized {
      shutdownDeletePaths.exists { path =>
        !absolutePath.equals(path) && absolutePath.startsWith(path)
      }
    }
    if (retval) {
      logInfo("path = " + file + ", already present as root for deletion.")
    }
    retval
  }

  // Note: if file is child of some registered path, while not equal to it, then return true;
  // else false. This is to ensure that two shutdown hooks do not try to delete each others
  // paths - resulting in Exception and incomplete cleanup.
  def hasRootAsShutdownDeleteDir(file: TachyonFile): Boolean = {
    val absolutePath = file.getPath()
    val retval = shutdownDeleteTachyonPaths.synchronized {
      shutdownDeleteTachyonPaths.exists { path =>
        !absolutePath.equals(path) && absolutePath.startsWith(path)
      }
    }
    if (retval) {
      logInfo("path = " + file + ", already present as root for deletion.")
    }
    retval
  }

  /** Create a temporary directory inside the given parent directory */
  def createTempDir(root: String = System.getProperty("java.io.tmpdir")): File = {
    var attempts = 0
    val maxAttempts = 10
    var dir: File = null
    while (dir == null) {
      attempts += 1
      if (attempts > maxAttempts) {
        throw new IOException("Failed to create a temp directory (under " + root + ") after " +
          maxAttempts + " attempts!")
      }
      try {
        dir = new File(root, "spark-" + UUID.randomUUID.toString)
        if (dir.exists() || !dir.mkdirs()) {
          dir = null
        }
      } catch { case e: IOException => ; }
    }

    registerShutdownDeleteDir(dir)

    // Add a shutdown hook to delete the temp dir when the JVM exits
    Runtime.getRuntime.addShutdownHook(new Thread("delete Spark temp dir " + dir) {
      override def run() {
        // Attempt to delete if some patch which is parent of this is not already registered.
        if (! hasRootAsShutdownDeleteDir(dir)) Utils.deleteRecursively(dir)
      }
    })
    dir
  }

  /** Copy all data from an InputStream to an OutputStream */
  def copyStream(in: InputStream,
                 out: OutputStream,
                 closeStreams: Boolean = false): Long =
  {
    var count = 0L
    try {
      if (in.isInstanceOf[FileInputStream] && out.isInstanceOf[FileOutputStream]) {
        // When both streams are File stream, use transferTo to improve copy performance.
        val inChannel = in.asInstanceOf[FileInputStream].getChannel()
        val outChannel = out.asInstanceOf[FileOutputStream].getChannel()
        val size = inChannel.size()

        // In case transferTo method transferred less data than we have required.
        while (count < size) {
          count += inChannel.transferTo(count, size - count, outChannel)
        }
      } else {
        val buf = new Array[Byte](8192)
        var n = 0
        while (n != -1) {
          n = in.read(buf)
          if (n != -1) {
            out.write(buf, 0, n)
            count += n
          }
        }
      }
      count
    } finally {
      if (closeStreams) {
        try {
          in.close()
        } finally {
          out.close()
        }
      }
    }
  }

  /**
   * Construct a URI container information used for authentication.
   * This also sets the default authenticator to properly negotiation the
   * user/password based on the URI.
   *
   * Note this relies on the Authenticator.setDefault being set properly to decode
   * the user name and password. This is currently set in the SecurityManager.
   */
  def constructURIForAuthentication(uri: URI, securityMgr: SecurityManager): URI = {
    val userCred = securityMgr.getSecretKey()
    if (userCred == null) throw new Exception("Secret key is null with authentication on")
    val userInfo = securityMgr.getHttpUser()  + ":" + userCred
    new URI(uri.getScheme(), userInfo, uri.getHost(), uri.getPort(), uri.getPath(),
      uri.getQuery(), uri.getFragment())
  }

  /**
   * Download a file requested by the executor. Supports fetching the file in a variety of ways,
   * including HTTP, HDFS and files on a standard filesystem, based on the URL parameter.
   *
   * Throws SparkException if the target file already exists and has different contents than
   * the requested file.
   */
  def fetchFile(url: String, targetDir: File, conf: SparkConf, securityMgr: SecurityManager,
    hadoopConf: Configuration) {
    val filename = url.split("/").last
    val tempDir = getLocalDir(conf)
    val tempFile =  File.createTempFile("fetchFileTemp", null, new File(tempDir))
    val targetFile = new File(targetDir, filename)
    val uri = new URI(url)
    val fileOverwrite = conf.getBoolean("spark.files.overwrite", defaultValue = false)
    uri.getScheme match {
      case "http" | "https" | "ftp" =>
        logInfo("Fetching " + url + " to " + tempFile)

        var uc: URLConnection = null
        if (securityMgr.isAuthenticationEnabled()) {
          logDebug("fetchFile with security enabled")
          val newuri = constructURIForAuthentication(uri, securityMgr)
          uc = newuri.toURL().openConnection()
          uc.setAllowUserInteraction(false)
        } else {
          logDebug("fetchFile not using security")
          uc = new URL(url).openConnection()
        }

        val timeout = conf.getInt("spark.files.fetchTimeout", 60) * 1000
        uc.setConnectTimeout(timeout)
        uc.setReadTimeout(timeout)
        uc.connect()
        val in = uc.getInputStream()
        val out = new FileOutputStream(tempFile)
        Utils.copyStream(in, out, closeStreams = true)
        if (targetFile.exists && !Files.equal(tempFile, targetFile)) {
          if (fileOverwrite) {
            targetFile.delete()
            logInfo(("File %s exists and does not match contents of %s, " +
              "replacing it with %s").format(targetFile, url, url))
          } else {
            tempFile.delete()
            throw new SparkException(
              "File " + targetFile + " exists and does not match contents of" + " " + url)
          }
        }
        Files.move(tempFile, targetFile)
      case "file" | null =>
        // In the case of a local file, copy the local file to the target directory.
        // Note the difference between uri vs url.
        val sourceFile = if (uri.isAbsolute) new File(uri) else new File(url)
        var shouldCopy = true
        if (targetFile.exists) {
          if (!Files.equal(sourceFile, targetFile)) {
            if (fileOverwrite) {
              targetFile.delete()
              logInfo(("File %s exists and does not match contents of %s, " +
                "replacing it with %s").format(targetFile, url, url))
            } else {
              throw new SparkException(
                "File " + targetFile + " exists and does not match contents of" + " " + url)
            }
          } else {
            // Do nothing if the file contents are the same, i.e. this file has been copied
            // previously.
            logInfo(sourceFile.getAbsolutePath + " has been previously copied to "
              + targetFile.getAbsolutePath)
            shouldCopy = false
          }
        }

        if (shouldCopy) {
          // The file does not exist in the target directory. Copy it there.
          logInfo("Copying " + sourceFile.getAbsolutePath + " to " + targetFile.getAbsolutePath)
          Files.copy(sourceFile, targetFile)
        }
      case _ =>
        // Use the Hadoop filesystem library, which supports file://, hdfs://, s3://, and others
        val fs = getHadoopFileSystem(uri, hadoopConf)
        val in = fs.open(new Path(uri))
        val out = new FileOutputStream(tempFile)
        Utils.copyStream(in, out, closeStreams = true)
        if (targetFile.exists && !Files.equal(tempFile, targetFile)) {
          if (fileOverwrite) {
            targetFile.delete()
            logInfo(("File %s exists and does not match contents of %s, " +
              "replacing it with %s").format(targetFile, url, url))
          } else {
            tempFile.delete()
            throw new SparkException(
              "File " + targetFile + " exists and does not match contents of" + " " + url)
          }
        }
        Files.move(tempFile, targetFile)
    }
    // Decompress the file if it's a .tar or .tar.gz
    if (filename.endsWith(".tar.gz") || filename.endsWith(".tgz")) {
      logInfo("Untarring " + filename)
      Utils.execute(Seq("tar", "-xzf", filename), targetDir)
    } else if (filename.endsWith(".tar")) {
      logInfo("Untarring " + filename)
      Utils.execute(Seq("tar", "-xf", filename), targetDir)
    }
    // Make the file executable - That's necessary for scripts
    FileUtil.chmod(targetFile.getAbsolutePath, "a+x")
  }

  /**
   * Get the path of a temporary directory.  Spark's local directories can be configured through
   * multiple settings, which are used with the following precedence:
   *
   *   - If called from inside of a YARN container, this will return a directory chosen by YARN.
   *   - If the SPARK_LOCAL_DIRS environment variable is set, this will return a directory from it.
   *   - Otherwise, if the spark.local.dir is set, this will return a directory from it.
   *   - Otherwise, this will return java.io.tmpdir.
   *
   * Some of these configuration options might be lists of multiple paths, but this method will
   * always return a single directory.
   */
  def getLocalDir(conf: SparkConf): String = {
    getOrCreateLocalRootDirs(conf)(0)
  }

  private[spark] def isRunningInYarnContainer(conf: SparkConf): Boolean = {
    // These environment variables are set by YARN.
    // For Hadoop 0.23.X, we check for YARN_LOCAL_DIRS (we use this below in getYarnLocalDirs())
    // For Hadoop 2.X, we check for CONTAINER_ID.
    conf.getenv("CONTAINER_ID") != null || conf.getenv("YARN_LOCAL_DIRS") != null
  }

  /**
   * Gets or creates the directories listed in spark.local.dir or SPARK_LOCAL_DIRS,
   * and returns only the directories that exist / could be created.
   *
   * If no directories could be created, this will return an empty list.
   */
  private[spark] def getOrCreateLocalRootDirs(conf: SparkConf): Array[String] = {
    val confValue = if (isRunningInYarnContainer(conf)) {
      // If we are in yarn mode, systems can have different disk layouts so we must set it
      // to what Yarn on this system said was available.
      getYarnLocalDirs(conf)
    } else {
      Option(conf.getenv("SPARK_LOCAL_DIRS")).getOrElse(
        conf.get("spark.local.dir", System.getProperty("java.io.tmpdir")))
    }
    val rootDirs = confValue.split(',')
    logDebug(s"Getting/creating local root dirs at '$confValue'")

    rootDirs.flatMap { rootDir =>
      val localDir: File = new File(rootDir)
      val foundLocalDir = localDir.exists || localDir.mkdirs()
      if (!foundLocalDir) {
        logError(s"Failed to create local root dir in $rootDir.  Ignoring this directory.")
        None
      } else {
        Some(rootDir)
      }
    }
  }

  /** Get the Yarn approved local directories. */
  private def getYarnLocalDirs(conf: SparkConf): String = {
    // Hadoop 0.23 and 2.x have different Environment variable names for the
    // local dirs, so lets check both. We assume one of the 2 is set.
    // LOCAL_DIRS => 2.X, YARN_LOCAL_DIRS => 0.23.X
    val localDirs = Option(conf.getenv("YARN_LOCAL_DIRS"))
      .getOrElse(Option(conf.getenv("LOCAL_DIRS"))
      .getOrElse(""))

    if (localDirs.isEmpty) {
      throw new Exception("Yarn Local dirs can't be empty")
    }
    localDirs
  }

  /**
   * Shuffle the elements of a collection into a random order, returning the
   * result in a new collection. Unlike scala.util.Random.shuffle, this method
   * uses a local random number generator, avoiding inter-thread contention.
   */
  def randomize[T: ClassTag](seq: TraversableOnce[T]): Seq[T] = {
    randomizeInPlace(seq.toArray)
  }

  /**
   * Shuffle the elements of an array into a random order, modifying the
   * original array. Returns the original array.
   */
  def randomizeInPlace[T](arr: Array[T], rand: Random = new Random): Array[T] = {
    for (i <- (arr.length - 1) to 1 by -1) {
      val j = rand.nextInt(i)
      val tmp = arr(j)
      arr(j) = arr(i)
      arr(i) = tmp
    }
    arr
  }

  /**
   * Get the local host's IP address in dotted-quad format (e.g. 1.2.3.4).
   * Note, this is typically not used from within core spark.
   */
  lazy val localIpAddress: String = findLocalIpAddress()
  lazy val localIpAddressHostname: String = getAddressHostName(localIpAddress)

  private def findLocalIpAddress(): String = {
    val defaultIpOverride = System.getenv("SPARK_LOCAL_IP")
    if (defaultIpOverride != null) {
      defaultIpOverride
    } else {
      val address = InetAddress.getLocalHost
      if (address.isLoopbackAddress) {
        // Address resolves to something like 127.0.1.1, which happens on Debian; try to find
        // a better address using the local network interfaces
        // getNetworkInterfaces returns ifs in reverse order compared to ifconfig output order
        // on unix-like system. On windows, it returns in index order.
        // It's more proper to pick ip address following system output order.
        val activeNetworkIFs = NetworkInterface.getNetworkInterfaces.toList
        val reOrderedNetworkIFs = if (isWindows) activeNetworkIFs else activeNetworkIFs.reverse
        for (ni <- reOrderedNetworkIFs) {
          for (addr <- ni.getInetAddresses if !addr.isLinkLocalAddress &&
               !addr.isLoopbackAddress && addr.isInstanceOf[Inet4Address]) {
            // We've found an address that looks reasonable!
            logWarning("Your hostname, " + InetAddress.getLocalHost.getHostName + " resolves to" +
              " a loopback address: " + address.getHostAddress + "; using " + addr.getHostAddress +
              " instead (on interface " + ni.getName + ")")
            logWarning("Set SPARK_LOCAL_IP if you need to bind to another address")
            return addr.getHostAddress
          }
        }
        logWarning("Your hostname, " + InetAddress.getLocalHost.getHostName + " resolves to" +
          " a loopback address: " + address.getHostAddress + ", but we couldn't find any" +
          " external IP address!")
        logWarning("Set SPARK_LOCAL_IP if you need to bind to another address")
      }
      address.getHostAddress
    }
  }

  private var customHostname: Option[String] = None

  /**
   * Allow setting a custom host name because when we run on Mesos we need to use the same
   * hostname it reports to the master.
   */
  def setCustomHostname(hostname: String) {
    // DEBUG code
    Utils.checkHost(hostname)
    customHostname = Some(hostname)
  }

  /**
   * Get the local machine's hostname.
   */
  def localHostName(): String = {
    customHostname.getOrElse(localIpAddressHostname)
  }

  def getAddressHostName(address: String): String = {
    InetAddress.getByName(address).getHostName
  }

  def checkHost(host: String, message: String = "") {
    assert(host.indexOf(':') == -1, message)
  }

  def checkHostPort(hostPort: String, message: String = "") {
    assert(hostPort.indexOf(':') != -1, message)
  }

  // Typically, this will be of order of number of nodes in cluster
  // If not, we should change it to LRUCache or something.
  private val hostPortParseResults = new ConcurrentHashMap[String, (String, Int)]()

  def parseHostPort(hostPort: String): (String,  Int) = {
    // Check cache first.
    val cached = hostPortParseResults.get(hostPort)
    if (cached != null) {
      return cached
    }

    val indx: Int = hostPort.lastIndexOf(':')
    // This is potentially broken - when dealing with ipv6 addresses for example, sigh ...
    // but then hadoop does not support ipv6 right now.
    // For now, we assume that if port exists, then it is valid - not check if it is an int > 0
    if (-1 == indx) {
      val retval = (hostPort, 0)
      hostPortParseResults.put(hostPort, retval)
      return retval
    }

    val retval = (hostPort.substring(0, indx).trim(), hostPort.substring(indx + 1).trim().toInt)
    hostPortParseResults.putIfAbsent(hostPort, retval)
    hostPortParseResults.get(hostPort)
  }

  private val daemonThreadFactoryBuilder: ThreadFactoryBuilder =
    new ThreadFactoryBuilder().setDaemon(true)

  /**
   * Create a thread factory that names threads with a prefix and also sets the threads to daemon.
   */
  def namedThreadFactory(prefix: String): ThreadFactory = {
    daemonThreadFactoryBuilder.setNameFormat(prefix + "-%d").build()
  }

  /**
   * Wrapper over newCachedThreadPool. Thread names are formatted as prefix-ID, where ID is a
   * unique, sequentially assigned integer.
   */
  def newDaemonCachedThreadPool(prefix: String): ThreadPoolExecutor = {
    val threadFactory = namedThreadFactory(prefix)
    Executors.newCachedThreadPool(threadFactory).asInstanceOf[ThreadPoolExecutor]
  }

  /**
   * Wrapper over newFixedThreadPool. Thread names are formatted as prefix-ID, where ID is a
   * unique, sequentially assigned integer.
   */
  def newDaemonFixedThreadPool(nThreads: Int, prefix: String): ThreadPoolExecutor = {
    val threadFactory = namedThreadFactory(prefix)
    Executors.newFixedThreadPool(nThreads, threadFactory).asInstanceOf[ThreadPoolExecutor]
  }

  /**
   * Return the string to tell how long has passed in milliseconds.
   */
  def getUsedTimeMs(startTimeMs: Long): String = {
    " " + (System.currentTimeMillis - startTimeMs) + " ms"
  }

  private def listFilesSafely(file: File): Seq[File] = {
    val files = file.listFiles()
    if (files == null) {
      throw new IOException("Failed to list files for dir: " + file)
    }
    files
  }

  /**
   * Delete a file or directory and its contents recursively.
   * Don't follow directories if they are symlinks.
   */
  def deleteRecursively(file: File) {
    if (file != null) {
      if (file.isDirectory() && !isSymlink(file)) {
        for (child <- listFilesSafely(file)) {
          deleteRecursively(child)
        }
      }
      if (!file.delete()) {
        // Delete can also fail if the file simply did not exist
        if (file.exists()) {
          throw new IOException("Failed to delete: " + file.getAbsolutePath)
        }
      }
    }
  }

  /**
   * Delete a file or directory and its contents recursively.
   */
  def deleteRecursively(dir: TachyonFile, client: TachyonFS) {
    if (!client.delete(dir.getPath(), true)) {
      throw new IOException("Failed to delete the tachyon dir: " + dir)
    }
  }

  /**
   * Check to see if file is a symbolic link.
   */
  def isSymlink(file: File): Boolean = {
    if (file == null) throw new NullPointerException("File must not be null")
    if (isWindows) return false
    val fileInCanonicalDir = if (file.getParent() == null) {
      file
    } else {
      new File(file.getParentFile().getCanonicalFile(), file.getName())
    }

    !fileInCanonicalDir.getCanonicalFile().equals(fileInCanonicalDir.getAbsoluteFile())
  }

  /**
   * Finds all the files in a directory whose last modified time is older than cutoff seconds.
   * @param dir  must be the path to a directory, or IllegalArgumentException is thrown
   * @param cutoff measured in seconds. Files older than this are returned.
   */
  def findOldFiles(dir: File, cutoff: Long): Seq[File] = {
    val currentTimeMillis = System.currentTimeMillis
    if (dir.isDirectory) {
      val files = listFilesSafely(dir)
      files.filter { file => file.lastModified < (currentTimeMillis - cutoff * 1000) }
    } else {
      throw new IllegalArgumentException(dir + " is not a directory!")
    }
  }

  /**
   * Convert a Java memory parameter passed to -Xmx (such as 300m or 1g) to a number of megabytes.
   */
  def memoryStringToMb(str: String): Int = {
    val lower = str.toLowerCase
    if (lower.endsWith("k")) {
      (lower.substring(0, lower.length-1).toLong / 1024).toInt
    } else if (lower.endsWith("m")) {
      lower.substring(0, lower.length-1).toInt
    } else if (lower.endsWith("g")) {
      lower.substring(0, lower.length-1).toInt * 1024
    } else if (lower.endsWith("t")) {
      lower.substring(0, lower.length-1).toInt * 1024 * 1024
    } else {// no suffix, so it's just a number in bytes
      (lower.toLong / 1024 / 1024).toInt
    }
  }

  /**
   * Convert a quantity in bytes to a human-readable string such as "4.0 MB".
   */
  def bytesToString(size: Long): String = {
    val TB = 1L << 40
    val GB = 1L << 30
    val MB = 1L << 20
    val KB = 1L << 10

    val (value, unit) = {
      if (size >= 2*TB) {
        (size.asInstanceOf[Double] / TB, "TB")
      } else if (size >= 2*GB) {
        (size.asInstanceOf[Double] / GB, "GB")
      } else if (size >= 2*MB) {
        (size.asInstanceOf[Double] / MB, "MB")
      } else if (size >= 2*KB) {
        (size.asInstanceOf[Double] / KB, "KB")
      } else {
        (size.asInstanceOf[Double], "B")
      }
    }
    "%.1f %s".formatLocal(Locale.US, value, unit)
  }

  /**
   * Returns a human-readable string representing a duration such as "35ms"
   */
  def msDurationToString(ms: Long): String = {
    val second = 1000
    val minute = 60 * second
    val hour = 60 * minute

    ms match {
      case t if t < second =>
        "%d ms".format(t)
      case t if t < minute =>
        "%.1f s".format(t.toFloat / second)
      case t if t < hour =>
        "%.1f m".format(t.toFloat / minute)
      case t =>
        "%.2f h".format(t.toFloat / hour)
    }
  }

  /**
   * Convert a quantity in megabytes to a human-readable string such as "4.0 MB".
   */
  def megabytesToString(megabytes: Long): String = {
    bytesToString(megabytes * 1024L * 1024L)
  }

  /**
   * Execute a command in the given working directory, throwing an exception if it completes
   * with an exit code other than 0.
   */
  def execute(command: Seq[String], workingDir: File) {
    val process = new ProcessBuilder(command: _*)
        .directory(workingDir)
        .redirectErrorStream(true)
        .start()
    new Thread("read stdout for " + command(0)) {
      override def run() {
        for (line <- Source.fromInputStream(process.getInputStream).getLines()) {
          System.err.println(line)
        }
      }
    }.start()
    val exitCode = process.waitFor()
    if (exitCode != 0) {
      throw new SparkException("Process " + command + " exited with code " + exitCode)
    }
  }

  /**
   * Execute a command and get its output, throwing an exception if it yields a code other than 0.
   */
  def executeAndGetOutput(
      command: Seq[String],
      workingDir: File = new File("."),
      extraEnvironment: Map[String, String] = Map.empty): String = {
    val builder = new ProcessBuilder(command: _*)
        .directory(workingDir)
    val environment = builder.environment()
    for ((key, value) <- extraEnvironment) {
      environment.put(key, value)
    }
    val process = builder.start()
    new Thread("read stderr for " + command(0)) {
      override def run() {
        for (line <- Source.fromInputStream(process.getErrorStream).getLines()) {
          System.err.println(line)
        }
      }
    }.start()
    val output = new StringBuffer
    val stdoutThread = new Thread("read stdout for " + command(0)) {
      override def run() {
        for (line <- Source.fromInputStream(process.getInputStream).getLines()) {
          output.append(line)
        }
      }
    }
    stdoutThread.start()
    val exitCode = process.waitFor()
    stdoutThread.join()   // Wait for it to finish reading output
    if (exitCode != 0) {
      logError(s"Process $command exited with code $exitCode: $output")
      throw new SparkException(s"Process $command exited with code $exitCode")
    }
    output.toString
  }

  /**
   * Execute a block of code that evaluates to Unit, forwarding any uncaught exceptions to the
   * default UncaughtExceptionHandler
   */
  def tryOrExit(block: => Unit) {
    try {
      block
    } catch {
      case e: ControlThrowable => throw e
      case t: Throwable => ExecutorUncaughtExceptionHandler.uncaughtException(t)
    }
  }

  /** Default filtering function for finding call sites using `getCallSite`. */
  private def coreExclusionFunction(className: String): Boolean = {
    // A regular expression to match classes of the "core" Spark API that we want to skip when
    // finding the call site of a method.
    val SPARK_CORE_CLASS_REGEX = """^org\.apache\.spark(\.api\.java)?(\.util)?(\.rdd)?\.[A-Z]""".r
    val SCALA_CLASS_REGEX = """^scala""".r
    val isSparkCoreClass = SPARK_CORE_CLASS_REGEX.findFirstIn(className).isDefined
    val isScalaClass = SCALA_CLASS_REGEX.findFirstIn(className).isDefined
    // If the class is a Spark internal class or a Scala class, then exclude.
    isSparkCoreClass || isScalaClass
  }

  /**
   * When called inside a class in the spark package, returns the name of the user code class
   * (outside the spark package) that called into Spark, as well as which Spark method they called.
   * This is used, for example, to tell users where in their code each RDD got created.
   *
   * @param skipClass Function that is used to exclude non-user-code classes.
   */
  def getCallSite(skipClass: String => Boolean = coreExclusionFunction): CallSite = {
    val trace = Thread.currentThread.getStackTrace().filterNot { ste: StackTraceElement =>
      // When running under some profilers, the current stack trace might contain some bogus
      // frames. This is intended to ensure that we don't crash in these situations by
      // ignoring any frames that we can't examine.
      ste == null || ste.getMethodName == null || ste.getMethodName.contains("getStackTrace")
    }

    // Keep crawling up the stack trace until we find the first function not inside of the spark
    // package. We track the last (shallowest) contiguous Spark method. This might be an RDD
    // transformation, a SparkContext function (such as parallelize), or anything else that leads
    // to instantiation of an RDD. We also track the first (deepest) user method, file, and line.
    var lastSparkMethod = "<unknown>"
    var firstUserFile = "<unknown>"
    var firstUserLine = 0
    var insideSpark = true
    var callStack = new ArrayBuffer[String]() :+ "<unknown>"

    for (el <- trace) {
      if (insideSpark) {
        if (skipClass(el.getClassName)) {
          lastSparkMethod = if (el.getMethodName == "<init>") {
            // Spark method is a constructor; get its class name
            el.getClassName.substring(el.getClassName.lastIndexOf('.') + 1)
          } else {
            el.getMethodName
          }
          callStack(0) = el.toString // Put last Spark method on top of the stack trace.
        } else {
          firstUserLine = el.getLineNumber
          firstUserFile = el.getFileName
          callStack += el.toString
          insideSpark = false
        }
      } else {
        callStack += el.toString
      }
    }
    val callStackDepth = System.getProperty("spark.callstack.depth", "20").toInt
    CallSite(
      shortForm = s"$lastSparkMethod at $firstUserFile:$firstUserLine",
      longForm = callStack.take(callStackDepth).mkString("\n"))
  }

  /** Return a string containing part of a file from byte 'start' to 'end'. */
  def offsetBytes(path: String, start: Long, end: Long): String = {
    val file = new File(path)
    val length = file.length()
    val effectiveEnd = math.min(length, end)
    val effectiveStart = math.max(0, start)
    val buff = new Array[Byte]((effectiveEnd-effectiveStart).toInt)
    val stream = new FileInputStream(file)

    try {
      stream.skip(effectiveStart)
      stream.read(buff)
    } finally {
      stream.close()
    }
    Source.fromBytes(buff).mkString
  }

  /**
   * Return a string containing data across a set of files. The `startIndex`
   * and `endIndex` is based on the cumulative size of all the files take in
   * the given order. See figure below for more details.
   */
  def offsetBytes(files: Seq[File], start: Long, end: Long): String = {
    val fileLengths = files.map { _.length }
    val startIndex = math.max(start, 0)
    val endIndex = math.min(end, fileLengths.sum)
    val fileToLength = files.zip(fileLengths).toMap
    logDebug("Log files: \n" + fileToLength.mkString("\n"))

    val stringBuffer = new StringBuffer((endIndex - startIndex).toInt)
    var sum = 0L
    for (file <- files) {
      val startIndexOfFile = sum
      val endIndexOfFile = sum + fileToLength(file)
      logDebug(s"Processing file $file, " +
        s"with start index = $startIndexOfFile, end index = $endIndex")

      /*
                                      ____________
       range 1:                      |            |
                                     |   case A   |

       files:   |==== file 1 ====|====== file 2 ======|===== file 3 =====|

                     |   case B  .       case C       .    case D    |
       range 2:      |___________.____________________.______________|
       */

      if (startIndex <= startIndexOfFile  && endIndex >= endIndexOfFile) {
        // Case C: read the whole file
        stringBuffer.append(offsetBytes(file.getAbsolutePath, 0, fileToLength(file)))
      } else if (startIndex > startIndexOfFile && startIndex < endIndexOfFile) {
        // Case A and B: read from [start of required range] to [end of file / end of range]
        val effectiveStartIndex = startIndex - startIndexOfFile
        val effectiveEndIndex = math.min(endIndex - startIndexOfFile, fileToLength(file))
        stringBuffer.append(Utils.offsetBytes(
          file.getAbsolutePath, effectiveStartIndex, effectiveEndIndex))
      } else if (endIndex > startIndexOfFile && endIndex < endIndexOfFile) {
        // Case D: read from [start of file] to [end of require range]
        val effectiveStartIndex = math.max(startIndex - startIndexOfFile, 0)
        val effectiveEndIndex = endIndex - startIndexOfFile
        stringBuffer.append(Utils.offsetBytes(
          file.getAbsolutePath, effectiveStartIndex, effectiveEndIndex))
      }
      sum += fileToLength(file)
      logDebug(s"After processing file $file, string built is ${stringBuffer.toString}}")
    }
    stringBuffer.toString
  }

  /**
   * Clone an object using a Spark serializer.
   */
  def clone[T: ClassTag](value: T, serializer: SerializerInstance): T = {
    serializer.deserialize[T](serializer.serialize(value))
  }

  /**
   * Detect whether this thread might be executing a shutdown hook. Will always return true if
   * the current thread is a running a shutdown hook but may spuriously return true otherwise (e.g.
   * if System.exit was just called by a concurrent thread).
   *
   * Currently, this detects whether the JVM is shutting down by Runtime#addShutdownHook throwing
   * an IllegalStateException.
   */
  def inShutdown(): Boolean = {
    try {
      val hook = new Thread {
        override def run() {}
      }
      Runtime.getRuntime.addShutdownHook(hook)
      Runtime.getRuntime.removeShutdownHook(hook)
    } catch {
      case ise: IllegalStateException => return true
    }
    false
  }

  private def isSpace(c: Char): Boolean = {
    " \t\r\n".indexOf(c) != -1
  }

  /**
   * Split a string of potentially quoted arguments from the command line the way that a shell
   * would do it to determine arguments to a command. For example, if the string is 'a "b c" d',
   * then it would be parsed as three arguments: 'a', 'b c' and 'd'.
   */
  def splitCommandString(s: String): Seq[String] = {
    val buf = new ArrayBuffer[String]
    var inWord = false
    var inSingleQuote = false
    var inDoubleQuote = false
    val curWord = new StringBuilder
    def endWord() {
      buf += curWord.toString
      curWord.clear()
    }
    var i = 0
    while (i < s.length) {
      val nextChar = s.charAt(i)
      if (inDoubleQuote) {
        if (nextChar == '"') {
          inDoubleQuote = false
        } else if (nextChar == '\\') {
          if (i < s.length - 1) {
            // Append the next character directly, because only " and \ may be escaped in
            // double quotes after the shell's own expansion
            curWord.append(s.charAt(i + 1))
            i += 1
          }
        } else {
          curWord.append(nextChar)
        }
      } else if (inSingleQuote) {
        if (nextChar == '\'') {
          inSingleQuote = false
        } else {
          curWord.append(nextChar)
        }
        // Backslashes are not treated specially in single quotes
      } else if (nextChar == '"') {
        inWord = true
        inDoubleQuote = true
      } else if (nextChar == '\'') {
        inWord = true
        inSingleQuote = true
      } else if (!isSpace(nextChar)) {
        curWord.append(nextChar)
        inWord = true
      } else if (inWord && isSpace(nextChar)) {
        endWord()
        inWord = false
      }
      i += 1
    }
    if (inWord || inDoubleQuote || inSingleQuote) {
      endWord()
    }
    buf
  }

 /* Calculates 'x' modulo 'mod', takes to consideration sign of x,
  * i.e. if 'x' is negative, than 'x' % 'mod' is negative too
  * so function return (x % mod) + mod in that case.
  */
  def nonNegativeMod(x: Int, mod: Int): Int = {
    val rawMod = x % mod
    rawMod + (if (rawMod < 0) mod else 0)
  }

  // Handles idiosyncracies with hash (add more as required)
  def nonNegativeHash(obj: AnyRef): Int = {

    // Required ?
    if (obj eq null) return 0

    val hash = obj.hashCode
    // math.abs fails for Int.MinValue
    val hashAbs = if (Int.MinValue != hash) math.abs(hash) else 0

    // Nothing else to guard against ?
    hashAbs
  }

  /** Returns a copy of the system properties that is thread-safe to iterator over. */
  def getSystemProperties(): Map[String, String] = {
    System.getProperties.clone().asInstanceOf[java.util.Properties].toMap[String, String]
  }

  /**
   * Method executed for repeating a task for side effects.
   * Unlike a for comprehension, it permits JVM JIT optimization
   */
  def times(numIters: Int)(f: => Unit): Unit = {
    var i = 0
    while (i < numIters) {
      f
      i += 1
    }
  }

  /**
   * Timing method based on iterations that permit JVM JIT optimization.
   * @param numIters number of iterations
   * @param f function to be executed
   */
  def timeIt(numIters: Int)(f: => Unit): Long = {
    val start = System.currentTimeMillis
    times(numIters)(f)
    System.currentTimeMillis - start
  }

  /**
   * Counts the number of elements of an iterator using a while loop rather than calling
   * [[scala.collection.Iterator#size]] because it uses a for loop, which is slightly slower
   * in the current version of Scala.
   */
  def getIteratorSize[T](iterator: Iterator[T]): Long = {
    var count = 0L
    while (iterator.hasNext) {
      count += 1L
      iterator.next()
    }
    count
  }

  /**
   * Creates a symlink. Note jdk1.7 has Files.createSymbolicLink but not used here
   * for jdk1.6 support.  Supports windows by doing copy, everything else uses "ln -sf".
   * @param src absolute path to the source
   * @param dst relative path for the destination
   */
  def symlink(src: File, dst: File) {
    if (!src.isAbsolute()) {
      throw new IOException("Source must be absolute")
    }
    if (dst.isAbsolute()) {
      throw new IOException("Destination must be relative")
    }
    var cmdSuffix = ""
    val linkCmd = if (isWindows) {
      // refer to http://technet.microsoft.com/en-us/library/cc771254.aspx
      cmdSuffix = " /s /e /k /h /y /i"
      "cmd /c xcopy "
    } else {
      cmdSuffix = ""
      "ln -sf "
    }
    import scala.sys.process._
    (linkCmd + src.getAbsolutePath() + " " + dst.getPath() + cmdSuffix) lines_!
    ProcessLogger(line => logInfo(line))
  }


  /** Return the class name of the given object, removing all dollar signs */
  def getFormattedClassName(obj: AnyRef) = {
    obj.getClass.getSimpleName.replace("$", "")
  }

  /** Return an option that translates JNothing to None */
  def jsonOption(json: JValue): Option[JValue] = {
    json match {
      case JNothing => None
      case value: JValue => Some(value)
    }
  }

  /** Return an empty JSON object */
  def emptyJson = JObject(List[JField]())

  /**
   * Return a Hadoop FileSystem with the scheme encoded in the given path.
   */
  def getHadoopFileSystem(path: URI, conf: Configuration): FileSystem = {
    FileSystem.get(path, conf)
  }

  /**
   * Return a Hadoop FileSystem with the scheme encoded in the given path.
   */
  def getHadoopFileSystem(path: String, conf: Configuration): FileSystem = {
    getHadoopFileSystem(new URI(path), conf)
  }

  /**
   * Return the absolute path of a file in the given directory.
   */
  def getFilePath(dir: File, fileName: String): Path = {
    assert(dir.isDirectory)
    val path = new File(dir, fileName).getAbsolutePath
    new Path(path)
  }

  /**
   * Whether the underlying operating system is Windows.
   */
  val isWindows = SystemUtils.IS_OS_WINDOWS

  /**
   * Pattern for matching a Windows drive, which contains only a single alphabet character.
   */
  val windowsDrive = "([a-zA-Z])".r

  /**
   * Format a Windows path such that it can be safely passed to a URI.
   */
  def formatWindowsPath(path: String): String = path.replace("\\", "/")

  /**
   * Indicates whether Spark is currently running unit tests.
   */
  def isTesting = {
    sys.env.contains("SPARK_TESTING") || sys.props.contains("spark.testing")
  }

  /**
   * Strip the directory from a path name
   */
  def stripDirectory(path: String): String = {
    new File(path).getName
  }

  /**
   * Wait for a process to terminate for at most the specified duration.
   * Return whether the process actually terminated after the given timeout.
   */
  def waitForProcess(process: Process, timeoutMs: Long): Boolean = {
    var terminated = false
    val startTime = System.currentTimeMillis
    while (!terminated) {
      try {
        process.exitValue()
        terminated = true
      } catch {
        case e: IllegalThreadStateException =>
          // Process not terminated yet
          if (System.currentTimeMillis - startTime > timeoutMs) {
            return false
          }
          Thread.sleep(100)
      }
    }
    true
  }

  /**
   * Return the stderr of a process after waiting for the process to terminate.
   * If the process does not terminate within the specified timeout, return None.
   */
  def getStderr(process: Process, timeoutMs: Long): Option[String] = {
    val terminated = Utils.waitForProcess(process, timeoutMs)
    if (terminated) {
      Some(Source.fromInputStream(process.getErrorStream).getLines().mkString("\n"))
    } else {
      None
    }
  }

  /**
   * Execute the given block, logging and re-throwing any uncaught exception.
   * This is particularly useful for wrapping code that runs in a thread, to ensure
   * that exceptions are printed, and to avoid having to catch Throwable.
   */
  def logUncaughtExceptions[T](f: => T): T = {
    try {
      f
    } catch {
      case ct: ControlThrowable =>
        throw ct
      case t: Throwable =>
        logError(s"Uncaught exception in thread ${Thread.currentThread().getName}", t)
        throw t
    }
  }

  /** Executes the given block in a Try, logging any uncaught exceptions. */
  def tryLog[T](f: => T): Try[T] = {
    try {
      val res = f
      scala.util.Success(res)
    } catch {
      case ct: ControlThrowable =>
        throw ct
      case t: Throwable =>
        logError(s"Uncaught exception in thread ${Thread.currentThread().getName}", t)
        scala.util.Failure(t)
    }
  }

  /** Returns true if the given exception was fatal. See docs for scala.util.control.NonFatal. */
  def isFatalError(e: Throwable): Boolean = {
    e match {
      case NonFatal(_) | _: InterruptedException | _: NotImplementedError | _: ControlThrowable =>
        false
      case _ =>
        true
    }
  }

  /**
   * Return a well-formed URI for the file described by a user input string.
   *
   * If the supplied path does not contain a scheme, or is a relative path, it will be
   * converted into an absolute path with a file:// scheme.
   */
  def resolveURI(path: String, testWindows: Boolean = false): URI = {

    // In Windows, the file separator is a backslash, but this is inconsistent with the URI format
    val windows = isWindows || testWindows
    val formattedPath = if (windows) formatWindowsPath(path) else path

    val uri = new URI(formattedPath)
    if (uri.getPath == null) {
      throw new IllegalArgumentException(s"Given path is malformed: $uri")
    }
    uri.getScheme match {
      case windowsDrive(d) if windows =>
        new URI("file:/" + uri.toString.stripPrefix("/"))
      case null =>
        // Preserve fragments for HDFS file name substitution (denoted by "#")
        // For instance, in "abc.py#xyz.py", "xyz.py" is the name observed by the application
        val fragment = uri.getFragment
        val part = new File(uri.getPath).toURI
        new URI(part.getScheme, part.getPath, fragment)
      case _ =>
        uri
    }
  }

  /** Resolve a comma-separated list of paths. */
  def resolveURIs(paths: String, testWindows: Boolean = false): String = {
    if (paths == null || paths.trim.isEmpty) {
      ""
    } else {
      paths.split(",").map { p => Utils.resolveURI(p, testWindows) }.mkString(",")
    }
  }

  /** Return all non-local paths from a comma-separated list of paths. */
  def nonLocalPaths(paths: String, testWindows: Boolean = false): Array[String] = {
    val windows = isWindows || testWindows
    if (paths == null || paths.trim.isEmpty) {
      Array.empty
    } else {
      paths.split(",").filter { p =>
        val formattedPath = if (windows) formatWindowsPath(p) else p
        new URI(formattedPath).getScheme match {
          case windowsDrive(d) if windows => false
          case "local" | "file" | null => false
          case _ => true
        }
      }
    }
  }

  /** Return a nice string representation of the exception, including the stack trace. */
  def exceptionString(e: Exception): String = {
    if (e == null) "" else exceptionString(getFormattedClassName(e), e.getMessage, e.getStackTrace)
  }

  /** Return a nice string representation of the exception, including the stack trace. */
  def exceptionString(
      className: String,
      description: String,
      stackTrace: Array[StackTraceElement]): String = {
    val desc = if (description == null) "" else description
    val st = if (stackTrace == null) "" else stackTrace.map("        " + _).mkString("\n")
    s"$className: $desc\n$st"
  }

  /**
   * Convert all spark properties set in the given SparkConf to a sequence of java options.
   */
  def sparkJavaOpts(conf: SparkConf, filterKey: (String => Boolean) = _ => true): Seq[String] = {
    conf.getAll
      .filter { case (k, _) => filterKey(k) }
      .map { case (k, v) => s"-D$k=$v" }
  }

  /**
   * Default maximum number of retries when binding to a port before giving up.
   */
  val portMaxRetries: Int = {
    if (sys.props.contains("spark.testing")) {
      // Set a higher number of retries for tests...
      sys.props.get("spark.port.maxRetries").map(_.toInt).getOrElse(100)
    } else {
      Option(SparkEnv.get)
        .flatMap(_.conf.getOption("spark.port.maxRetries"))
        .map(_.toInt)
        .getOrElse(16)
    }
  }

  /**
   * Attempt to start a service on the given port, or fail after a number of attempts.
   * Each subsequent attempt uses 1 + the port used in the previous attempt (unless the port is 0).
   *
   * @param startPort The initial port to start the service on.
   * @param maxRetries Maximum number of retries to attempt.
   *                   A value of 3 means attempting ports n, n+1, n+2, and n+3, for example.
   * @param startService Function to start service on a given port.
   *                     This is expected to throw java.net.BindException on port collision.
   */
  def startServiceOnPort[T](
      startPort: Int,
      startService: Int => (T, Int),
      serviceName: String = "",
      maxRetries: Int = portMaxRetries): (T, Int) = {
    val serviceString = if (serviceName.isEmpty) "" else s" '$serviceName'"
    for (offset <- 0 to maxRetries) {
      // Do not increment port if startPort is 0, which is treated as a special port
      val tryPort = if (startPort == 0) startPort else (startPort + offset) % (65536 - 1024) + 1024
      try {
        val (service, port) = startService(tryPort)
        logInfo(s"Successfully started service$serviceString on port $port.")
        return (service, port)
      } catch {
        case e: Exception if isBindCollision(e) =>
          if (offset >= maxRetries) {
            val exceptionMessage =
              s"${e.getMessage}: Service$serviceString failed after $maxRetries retries!"
            val exception = new BindException(exceptionMessage)
            // restore original stack trace
            exception.setStackTrace(e.getStackTrace)
            throw exception
          }
          logWarning(s"Service$serviceString could not bind on port $tryPort. " +
            s"Attempting port ${tryPort + 1}.")
      }
    }
    // Should never happen
    throw new SparkException(s"Failed to start service$serviceString on port $startPort")
  }

  /**
   * Return whether the exception is caused by an address-port collision when binding.
   */
  def isBindCollision(exception: Throwable): Boolean = {
    exception match {
      case e: BindException =>
        if (e.getMessage != null && e.getMessage.contains("Address already in use")) {
          return true
        }
        isBindCollision(e.getCause)
      case e: MultiException => e.getThrowables.exists(isBindCollision)
      case e: Exception => isBindCollision(e.getCause)
      case _ => false
    }
  }

  /**
   * config a log4j properties used for testsuite
   */
  def configTestLog4j(level: String): Unit = {
    val pro = new Properties()
    pro.put("log4j.rootLogger", s"$level, console")
    pro.put("log4j.appender.console", "org.apache.log4j.ConsoleAppender")
    pro.put("log4j.appender.console.target", "System.err")
    pro.put("log4j.appender.console.layout", "org.apache.log4j.PatternLayout")
    pro.put("log4j.appender.console.layout.ConversionPattern",
      "%d{yy/MM/dd HH:mm:ss} %p %c{1}: %m%n")
    PropertyConfigurator.configure(pro)
  }

}

/**
 * A utility class to redirect the child process's stdout or stderr.
 */
private[spark] class RedirectThread(in: InputStream, out: OutputStream, name: String)
  extends Thread(name) {

  setDaemon(true)
  override def run() {
    scala.util.control.Exception.ignoring(classOf[IOException]) {
      // FIXME: We copy the stream on the level of bytes to avoid encoding problems.
      val buf = new Array[Byte](1024)
      var len = in.read(buf)
      while (len != -1) {
        out.write(buf, 0, len)
        out.flush()
        len = in.read(buf)
      }
    }
  }
}