bracket-scalaz.scala

import java.io._
import scala.concurrent.ExecutionContext.Implicits.global
import scala.util.control.NonFatal
import scala.concurrent.duration._
import scalaz._
import scalaz.effect._

object Sample extends SafeApp {
  def run(args: List[String]): IO[Unit] =
    for {
      _ <- generate      
      f <- acquire.bracket(release)(readFile).fork
      _ <- IO.unit.delay(500.millis)
      _ <- f.interrupt(new RuntimeException("Boo"))
      _ <- IO.unit.delay(1000.millis)
      _ <- f.join
    } yield ()

  def readFile(in: BufferedReader): IO[String] =
    IO.async { cb =>
      global.execute(new Runnable {
        def run() = {
          try {
            System.out.println("Started!")
            Thread.sleep(1000)
            val buffer = new StringBuffer()
            var continue = true
            
            while (continue) {
              val line = in.readLine()
              continue = line != null
              if (continue) buffer.append(line)
            }
            cb(\/-(buffer.toString))
          } catch {
            case NonFatal(ex) => 
              System.err.println(s"Thrown! ${ex}")
              cb(-\/(ex))
          }
        }
      })
    }

  def release(in: BufferedReader): IO[Unit] =
    IO.sync(in.close())

  val acquire: IO[BufferedReader] =
    IO.sync(new BufferedReader(new InputStreamReader(new FileInputStream("/tmp/test"), "utf-8")))

  val generate: IO[Unit] = 
    IO.sync {
      val out = new BufferedWriter(new OutputStreamWriter(new FileOutputStream("/tmp/test"), "utf-8"))
      for (_ <- 0 until 100) out.write("xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx\n")
      out.close()
    }
}