Allow to send Spark logs to the Almond kernel console output

Can be useful for debugging

modules/almond-spark/src/main/scala/org/apache/spark/sql/NotebookSparkSession.scala

@@ -1,5 +1,6 @@
 package org.apache.spark.sql
 
+import almond.api.JupyterApi
 import almond.interpreter.api.{CommHandler, OutputHandler}
 import ammonite.repl.api.ReplAPI
 import ammonite.interp.api.InterpAPI
@@ -11,7 +12,8 @@ object NotebookSparkSession {
     interpApi: InterpAPI,
     replApi: ReplAPI,
     publish: OutputHandler,
-    commHandler: CommHandler
+    commHandler: CommHandler,
+    jupyterApi: JupyterApi
   ): NotebookSparkSessionBuilder =
     new NotebookSparkSessionBuilder
 

modules/almond-spark/src/main/scala/org/apache/spark/sql/almondinternals/NotebookSparkSessionBuilder.scala

@@ -3,6 +3,7 @@ package org.apache.spark.sql.almondinternals
 import java.io.File
 import java.lang.{Boolean => JBoolean}
 
+import almond.api.JupyterApi
 import almond.interpreter.api.{CommHandler, OutputHandler}
 import almond.display.Display.html
 import ammonite.interp.api.InterpAPI
@@ -19,7 +20,8 @@ class NotebookSparkSessionBuilder(implicit
   interpApi: InterpAPI,
   replApi: ReplAPI,
   publish: OutputHandler,
-  commHandler: CommHandler
+  commHandler: CommHandler,
+  jupyterApi: JupyterApi
 ) extends AmmoniteSparkSessionBuilder {
 
   override def toString = "NotebookSparkSessionBuilder"
@@ -37,6 +39,11 @@ class NotebookSparkSessionBuilder(implicit
   private var useBars0  = false
 
   private var logsInDeveloperConsoleOpt = Option.empty[Boolean]
+  private var logsInKernelOutputOpt     = Option.empty[Boolean]
+
+  private def defaultLogsInKernelOutput() =
+    Option(System.getenv("ALMOND_SPARK_LOGS_IN_KERNEL_OUTPUT"))
+      .exists(v => v == "1" || v == "true")
 
   def progress(
     enable: Boolean = true,
@@ -54,6 +61,11 @@ class NotebookSparkSessionBuilder(implicit
     this
   }
 
+  def logsInKernelOutput(enable: JBoolean = null): this.type = {
+    logsInKernelOutputOpt = Option[JBoolean](enable).map[Boolean](x => x)
+    this
+  }
+
   override def getOrCreate(): SparkSession = {
 
     def defaultLogFileOpt = {
@@ -78,13 +90,23 @@ class NotebookSparkSessionBuilder(implicit
         defaultLogFileOpt
     }
 
-    var sendLogOpt = Option.empty[SendLog]
+    var sendLogOpt          = Option.empty[SendLog]
+    var sendLogToConsoleOpt = Option.empty[SendLogToConsole]
 
     try {
       sendLogOpt = logFileOpt.map { f =>
         SendLog.start(f)
       }
 
+      if (logsInKernelOutputOpt.contains(true) && defaultLogFileOpt.isEmpty)
+        Console.err.println(
+          "Warning: cannot determine log file, logs won't be sent to the kernel console."
+        )
+      if (logsInKernelOutputOpt.getOrElse(defaultLogsInKernelOutput()))
+        sendLogToConsoleOpt = defaultLogFileOpt.map { f =>
+          SendLogToConsole.start(f)
+        }
+
       val session = super.getOrCreate()
 
       val reverseProxyUrlOpt = session.sparkContext.getConf.getOption("spark.ui.reverseProxyUrl")
@@ -106,8 +128,10 @@ class NotebookSparkSessionBuilder(implicit
 
       session.sparkContext.addSparkListener(
         new SparkListener {
-          override def onApplicationEnd(applicationEnd: SparkListenerApplicationEnd) =
+          override def onApplicationEnd(applicationEnd: SparkListenerApplicationEnd) = {
             sendLogOpt.foreach(_.stop())
+            sendLogToConsoleOpt.foreach(_.stop())
+          }
         }
       )
 
@@ -116,6 +140,7 @@ class NotebookSparkSessionBuilder(implicit
     catch {
       case NonFatal(e) =>
         sendLogOpt.foreach(_.stop())
+        sendLogToConsoleOpt.foreach(_.stop())
         throw e
     }
   }

modules/almond-spark/src/main/scala/org/apache/spark/sql/almondinternals/SendLogToConsole.scala

@@ -0,0 +1,95 @@
+package org.apache.spark.sql.almondinternals
+
+import almond.api.JupyterApi
+
+import java.io.{BufferedReader, File, FileReader, PrintStream}
+import java.nio.file.{Files, StandardOpenOption}
+
+import scala.collection.mutable.ListBuffer
+import scala.concurrent.duration.{DurationInt, FiniteDuration}
+
+final class SendLogToConsole(
+  f: File,
+  out: PrintStream,
+  threadName: String = "send-log-console",
+  lineBufferSize: Int = 10,
+  delay: FiniteDuration = 2.seconds
+) {
+
+  @volatile private var keepReading = true
+
+  val thread: Thread =
+    new Thread(threadName) {
+      override def run(): Unit = {
+
+        var r: FileReader = null
+
+        try {
+          // https://stackoverflow.com/questions/557844/java-io-implementation-of-unix-linux-tail-f/558262#558262
+
+          r = new FileReader(f)
+          val br = new BufferedReader(r)
+
+          var lines = new ListBuffer[String]
+          while (keepReading) {
+            val line = br.readLine()
+            if (line == null)
+              // wait until there is more in the file
+              Thread.sleep(delay.toMillis)
+            else {
+              lines += line
+
+              while (keepReading && lines.length <= lineBufferSize && br.ready())
+                lines += br.readLine()
+
+              val l = lines.result()
+              lines.clear()
+
+              for (line <- l)
+                out.println(line)
+            }
+          }
+        }
+        catch {
+          case _: InterruptedException =>
+          // normal exit
+          case e: Throwable =>
+            System.err.println(s"Thread $threadName crashed")
+            e.printStackTrace(System.err)
+        }
+        finally
+          if (r != null)
+            r.close()
+      }
+    }
+
+  def start(): Unit = {
+    assert(keepReading, "Already stopped")
+    if (!thread.isAlive)
+      synchronized {
+        if (!thread.isAlive)
+          thread.start()
+      }
+  }
+
+  def stop(): Unit = {
+    keepReading = false
+    thread.interrupt()
+  }
+
+}
+
+object SendLogToConsole {
+
+  def start(f: File)(implicit jupyterApi: JupyterApi): SendLogToConsole = {
+
+    // It seems the file must exist for the reader above to get content appended to it.
+    if (!f.exists())
+      Files.write(f.toPath, Array.emptyByteArray, StandardOpenOption.CREATE)
+
+    val sendLog = new SendLogToConsole(f, jupyterApi.consoleErr)
+    sendLog.start()
+    sendLog
+  }
+
+}

project/deps.sc

@@ -6,7 +6,7 @@ object Versions {
 
   def scala = Seq(scala213, scala212)
 
-  def almond        = "0.14.0-RC8"
+  def almond        = "0.14.0-RC9"
   def ammonite      = "3.0.0-M0-41-26a93d9c"
   def jsoniterScala = "2.13.5"
 }