Scala example source code file (DotRunner.scala)

This example Scala source code file (DotRunner.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

bufferedreader, cleanup, compiler, concurrent, dot, dotprocess, exception, inputstream, nsc, process, string, system, these, throwable, unit

The DotRunner.scala Scala example source code

package scala.tools.nsc
package doc
package html
package page
package diagram

import java.io.InputStream
import java.io.OutputStream
import java.io.InputStreamReader
import java.io.OutputStreamWriter
import java.io.BufferedWriter
import java.io.BufferedReader
import scala.sys.process._
import scala.concurrent.SyncVar

import model._

/** This class takes care of running the graphviz dot utility */
class DotRunner(settings: doc.Settings) {

  private[this] var dotRestarts = 0
  private[this] var dotProcess: DotProcess  = null

  def feedToDot(dotInput: String, template: DocTemplateEntity): String = {

    if (dotProcess == null) {
      if (dotRestarts < settings.docDiagramsDotRestart.value) {
        if (dotRestarts != 0)
          settings.printMsg("Graphviz will be restarted...\n")
        dotRestarts += 1
        dotProcess = new DotProcess(settings)
      } else
        return null
    }

    val tStart = System.currentTimeMillis
    val result = dotProcess.feedToDot(dotInput, template.qualifiedName)
    val tFinish = System.currentTimeMillis
    DiagramStats.addDotRunningTime(tFinish - tStart)

    if (result == null) {
      dotProcess.cleanup()
      dotProcess = null
      if (dotRestarts == settings.docDiagramsDotRestart.value) {
        settings.printMsg("\n")
        settings.printMsg("**********************************************************************")
        settings.printMsg("Diagrams will be disabled for this run because the graphviz dot tool")
        settings.printMsg("has malfunctioned too many times. These scaladoc flags may help:")
        settings.printMsg("")
        val baseList = List(settings.docDiagramsDebug,
                            settings.docDiagramsDotPath,
                            settings.docDiagramsDotRestart,
                            settings.docDiagramsDotTimeout)
        val width    = (baseList map (_.helpSyntax.length)).max
        def helpStr(s: doc.Settings#Setting) = ("%-" + width + "s") format (s.helpSyntax) + "  " + s.helpDescription
        baseList.foreach((sett: doc.Settings#Setting) => settings.printMsg(helpStr(sett)))
        settings.printMsg("\nPlease note that graphviz package version 2.26 or above is required.")
        settings.printMsg("**********************************************************************\n\n")

      }
    }

    result
  }

  def cleanup() =
    if (dotProcess != null)
      dotProcess.cleanup()
}

class DotProcess(settings: doc.Settings) {

  @volatile var error: Boolean = false           // signal an error
  val inputString = new SyncVar[String]                 // used for the dot process input
  val outputString = new SyncVar[String]                // used for the dot process output
  val errorBuffer: StringBuffer = new StringBuffer() // buffer used for both dot process error console AND logging

  // set in only one place, in the main thread
  var process: Process = null
  var templateName: String = ""
  var templateInput: String = ""

  def feedToDot(input: String, template: String): String = {

    templateName = template
    templateInput = input

    try {

      // process creation
      if (process == null) {
        val procIO = new ProcessIO(inputFn(_), outputFn(_), errorFn(_))
        val processBuilder: ProcessBuilder = Seq(settings.docDiagramsDotPath.value, "-Tsvg")
        process = processBuilder.run(procIO)
      }

      // pass the input and wait for the output
      assert(!inputString.isSet)
      assert(!outputString.isSet)
      inputString.put(input)
      var result = outputString.take(settings.docDiagramsDotTimeout.value * 1000L)
      if (error) result = null

      result

    } catch {
      case exc: Throwable =>
        errorBuffer.append("  Main thread in " + templateName + ": " +
          (if (exc.isInstanceOf[NoSuchElementException]) "Timeout" else "Exception: " + exc))
        error = true
        return null
    }
  }

  def cleanup(): Unit = {

    // we'll need to know if there was any error for reporting
    val _error = error

    if (process != null) {
      // if there's no error, this should exit cleanly
      if (!error) feedToDot("<finish>", "<finishing>")

      // just in case there's any thread hanging, this will take it out of the loop
      error = true
      process.destroy()
      // we'll need to unblock the input again
      if (!inputString.isSet) inputString.put("")
      if (outputString.isSet) outputString.take()
    }

    if (_error) {
      if (settings.docDiagramsDebug.value) {
        settings.printMsg("\n**********************************************************************")
        settings.printMsg("The graphviz dot diagram tool has malfunctioned and will be restarted.")
        settings.printMsg("\nThe following is the log of the failure:")
        settings.printMsg(errorBuffer.toString)
        settings.printMsg("  Cleanup: Last template: " + templateName)
        settings.printMsg("  Cleanup: Last dot input: \n    " + templateInput.replaceAll("\n","\n    ") + "\n")
        settings.printMsg("  Cleanup: Dot path: " + settings.docDiagramsDotPath.value)
        if (process != null)
          settings.printMsg("  Cleanup: Dot exit code: " + process.exitValue)
        settings.printMsg("**********************************************************************")
      } else {
        // we shouldn't just sit there for 50s not reporting anything, no?
        settings.printMsg("Graphviz dot encountered an error when generating the diagram for:")
        settings.printMsg(templateName)
        settings.printMsg("These are usually spurious errors, but if you notice a persistant error on")
        settings.printMsg("a diagram, please use the " + settings.docDiagramsDebug.name + " flag and report a bug with the output.")
      }
    }
  }

  /* The standard input passing function */
  private[this] def inputFn(stdin: OutputStream): Unit = {
    val writer = new BufferedWriter(new OutputStreamWriter(stdin))
    try {
      var input = inputString.take()

      while (!error) {
        if (input == "<finish>") {
          // empty => signal to finish
          stdin.close()
          return
        } else {
          // send output to dot
          writer.write(input + "\n\n")
          writer.flush()
        }

        if (!error) input = inputString.take()
      }
      stdin.close()
    } catch {
      case exc: Throwable =>
        error = true
        stdin.close()
        errorBuffer.append("  Input thread in " + templateName + ": Exception: " + exc + "\n")
    }
  }

  private[this] def outputFn(stdOut: InputStream): Unit = {
    val reader = new BufferedReader(new InputStreamReader(stdOut))
    val buffer: StringBuilder = new StringBuilder()
    try {
      var line = reader.readLine
      while (!error && line != null) {
        buffer.append(line + "\n")
        // signal the last element in the svg (only for output)
        if (line == "</svg>") {
          outputString.put(buffer.toString)
          buffer.setLength(0)
        }
        if (error) { stdOut.close(); return }
        line = reader.readLine
      }
      assert(!outputString.isSet)
      outputString.put(buffer.toString)
      stdOut.close()
    } catch {
      case exc: Throwable =>
        error = true
        stdOut.close()
        errorBuffer.append("  Output thread in " + templateName + ": Exception: " + exc + "\n")
    }
  }

  private[this] def errorFn(stdErr: InputStream): Unit = {
    val reader = new BufferedReader(new InputStreamReader(stdErr))
    try {
      var line = reader.readLine
      while (line != null) {
        errorBuffer.append("  DOT <error console>: " + line + "\n")
        error = true
        line = reader.readLine
      }
      stdErr.close()
    } catch {
      case exc: Throwable =>
        error = true
        stdErr.close()
        errorBuffer.append("  Error thread in " + templateName + ": Exception: " + exc + "\n")
    }
  }
}