Why does this code fail to delete the file? - scala

Question

An example from «Learning concurrent programming in Scala»:
package org.learningconcurrency
import java.io.File
import java.util.concurrent.atomic.AtomicReference
import java.util.concurrent.{ConcurrentHashMap, ForkJoinPool, LinkedBlockingQueue}
import org.apache.commons.io.FileUtils
import scala.annotation.tailrec
/**
* Created by kaiyin on 1/19/16.
*/
import org.learningconcurrency.ch3.Ch3.execute
import scala.collection.convert.decorateAsScala._
object Issue {
sealed trait State
class Idle extends State
class Creating extends State
class Copying(val n: Int) extends State
class Deleting extends State
class Entry(val isDir: Boolean) {
val state = new AtomicReference[State](new Idle)
}
class FileSystem(val root: String) {
val rootDir = new File(root)
val files: collection.concurrent.Map[String, Entry] = new ConcurrentHashMap[String, Entry]().asScala
for (f <- FileUtils.iterateFiles(rootDir, null, false).asScala)
files.put(f.getName, new Entry(false))
def deleteFile(filename: String): Unit = {
files.get(filename) match {
case None =>
log(s"Path '$filename' does not exist!")
case Some(entry) if entry.isDir =>
log(s"Path '$filename' is a directory!")
case Some(entry) => execute {
if (prepareForDelete(entry))
if (FileUtils.deleteQuietly(new File(filename)))
files.remove(filename)
}
}
}
}
#tailrec private def prepareForDelete(entry: Entry): Boolean = {
val s0 = entry.state.get
s0 match {
case i: Idle =>
if (entry.state.compareAndSet(s0, new Deleting)) true
else prepareForDelete(entry)
case c: Creating =>
log("File is being created, cannot delete")
false
case c: Copying =>
log("File is being created, cannot delete")
false
case d: Deleting =>
false
}
}
def main(args: Array[String]) {
val fs = new FileSystem("/tmp")
fs.files.foreach(println _)
// Thread.sleep(500)
fs.deleteFile("test")
}
}
It just checks the state of one file and then deletes it, and the code looks like it should work, but after running it, the file I have created by touch /tmp/test is still there.

Answer 1

The problem is related to FileUtils.deleteQuietly(new File(filename)) line. According to the docs, deleteQuietly does the same as File.delete(), but instead of raising exceptions, it just returns true if the file was deleted and false if it was not.
Adding a debugging log would show that deleteQuietly is not working:
if (FileUtils.deleteQuietly(new File(filename))) {
println("File was deleted!")
files.remove(filename)
} else {
println("File was NOT deleted!")
}
It should print File was NOT deleted.
So what's wrong? Let's inspect the parameter you passed to deleteQuietly:
println((new File(filename)).exists()) // returns false
It seems that File didn't found your file. What is missing?
Since you are only providing the relative path test, you need also to provide the parent directory:
case Some(entry) => execute {
if (prepareForDelete(entry))
if (FileUtils.deleteQuietly(new File(rootDir, filename)))
files.remove(filename)
}