Scala example source code file (Origins.scala)

This example Scala source code file (Origins.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

collection, int, multiline, oneline, originid, origins, rep, stackslice, stacktraceelement, string, t

The Origins.scala Scala example source code

/* NSC -- new scala compiler
 * Copyright 2005-2013 LAMP/EPFL
 * @author Paul Phillips
 */

package scala
package reflect
package internal.util

import scala.collection.{ mutable, immutable }

/** A debugging class for logging from whence a method is being called.
 *  Say you wanted to discover who was calling phase_= in SymbolTable.
 *  You could do this:
 *
 *  {{{
 *    private lazy val origins = Origins("arbitraryTag")
 *    // Commented out original enclosed for contrast
 *    // final def phase_=(p: Phase): Unit = {
 *    final def phase_=(p: Phase): Unit = origins {
 *  }}}
 *
 *  And that's it.  When the JVM exits it would issue a report something like this:
 {{{
 >> Origins tag 'arbitraryTag' logged 145585 calls from 51 distinguished sources.

   71114   scala.tools.nsc.symtab.Symbols$Symbol.unsafeTypeParams(Symbols.scala:862)
   16584   scala.tools.nsc.symtab.Symbols$Symbol.rawInfo(Symbols.scala:757)
   15411   scala.tools.nsc.symtab.Symbols$Symbol.unsafeTypeParams(Symbols.scala:869)
   11507   scala.tools.nsc.symtab.Symbols$Symbol.rawInfo(Symbols.scala:770)
   10285   scala.tools.nsc.symtab.Symbols$Symbol.unsafeTypeParams(Symbols.scala:864)
    6860   scala.tools.nsc.transform.SpecializeTypes.specializedTypeVars(SpecializeTypes.scala:304)
    ...
 }}}
 *
 */
abstract class Origins {
  type Rep
  type StackSlice = Array[StackTraceElement]

  def tag: String
  def isCutoff(el: StackTraceElement): Boolean
  def newRep(xs: StackSlice): Rep
  def repString(rep: Rep): String

  private val origins      = new mutable.HashMap[Rep, Int] withDefaultValue 0
  private def add(xs: Rep) = origins(xs) += 1
  private def total        = origins.values.foldLeft(0L)(_ + _)

  // Create a stack and whittle it down to the interesting part.
  def readStack(): Array[StackTraceElement] = (
    Thread.currentThread.getStackTrace dropWhile (x => !isCutoff(x)) dropWhile isCutoff drop 1
  )

  def apply[T](body: => T): T = {
    add(newRep(readStack()))
    body
  }
  def clear() = origins.clear()
  def show()  = {
    println("\n>> Origins tag '%s' logged %s calls from %s distinguished sources.\n".format(tag, total, origins.keys.size))
    origins.toList sortBy (-_._2) foreach {
      case (k, v) => println("%7s %s".format(v, repString(k)))
    }
  }
  def purge() = {
    show()
    clear()
  }
}

object Origins {
  private val counters  = mutable.HashMap[String, Origins]()
  private val thisClass = this.getClass.getName

  locally {
    sys.addShutdownHook(counters.values foreach (_.purge()))
  }

  case class OriginId(className: String, methodName: String) {
    def matches(el: StackTraceElement) = (
      (methodName == el.getMethodName) && (className startsWith el.getClassName)
    )
  }

  def lookup(tag: String, orElse: String => Origins): Origins =
    counters.getOrElseUpdate(tag, orElse(tag))
  def register(x: Origins): Origins = {
    counters(x.tag) = x
    x
  }

  private def preCutoff(el: StackTraceElement) = (
       (el.getClassName == thisClass)
    || (el.getClassName startsWith "java.lang.")
  )
  private def findCutoff() = {
    val cutoff = (Thread.currentThread.getStackTrace dropWhile preCutoff).head
    OriginId(cutoff.getClassName, cutoff.getMethodName)
  }

  def apply(tag: String): Origins              = counters.getOrElseUpdate(tag, new OneLine(tag, findCutoff()))
  def apply(tag: String, frames: Int): Origins = counters.getOrElseUpdate(tag, new MultiLine(tag, findCutoff(), frames))

  class OneLine(val tag: String, id: OriginId) extends Origins {
    type Rep                            = StackTraceElement
    def isCutoff(el: StackTraceElement) = id matches el
    def newRep(xs: StackSlice): Rep     = if ((xs eq null) || (xs.length == 0)) null else xs(0)
    def repString(rep: Rep)             = "  " + rep
  }
  class MultiLine(val tag: String, id: OriginId, numLines: Int) extends Origins {
    type Rep                            = List[StackTraceElement]
    def isCutoff(el: StackTraceElement) = id matches el
    def newRep(xs: StackSlice): Rep     = (xs take numLines).toList
    def repString(rep: Rep)             = rep.map("\n  " + _).mkString
    override def readStack()            = super.readStack() drop 1
  }
}