Scala retry

retry.scala

import scala.concurrent.Await
import scala.concurrent.ExecutionContext
import scala.concurrent.Future
import scala.concurrent.blocking
import scala.concurrent.duration.Deadline
import scala.concurrent.duration.Duration
import scala.concurrent.duration.DurationInt
import scala.concurrent.duration.DurationLong
import scala.concurrent.future
import scala.concurrent.promise

object Retry {

  /**
   * exponential back off for retry
   */
  def exponentialBackoff(r: Int): Duration = scala.math.pow(2, r).round * 100 milliseconds

  def noIgnore(t: Throwable): Boolean = false

  /**
   * retry a particular block that can fail
   *
   * @param maxRetry  how many times to retry before to giveup
   * @param deadline	how long to retry before giving up; default None
   * @param backoff		a back-off function that returns a Duration after which to retry. default is an exponential backoff at 100 milliseconds steps
   * @param ignoreThrowable		if you want to stop retrying on a particular exception
   * @param block	a block of code to retry
   * @param ctx	an execution context where to execute the block
   * @returns	an eventual Future succeeded with the value computed or failed with one of:
   *   `TooManyRetriesException`	if there were too many retries without an exception being caught. Probably impossible if you pass decent parameters
   *   `DeadlineExceededException` if the retry didn't succeed before the provided deadline
   *   `TimeoutException`	if you provide a deadline and the block takes too long to execute
   *   `Throwable`	the last encountered exception
   */
  def retry[T](maxRetry: Int,
    deadline: Option[Deadline] = None,
    backoff: (Int) => Duration = exponentialBackoff,
    ignoreThrowable: Throwable => Boolean = noIgnore)(block: => T)(implicit ctx: ExecutionContext): Future[T] = {

    class TooManyRetriesException extends Exception("too many retries without exception")
    class DeadlineExceededException extends Exception("deadline exceded")

    val p = promise[T]

    def recursiveRetry(retryCnt: Int, exception: Option[Throwable])(f: () => T): Option[T] = {
      if (maxRetry == retryCnt
        || deadline.isDefined && deadline.get.isOverdue) {
        exception match {
          case Some(t) =>
            p failure t
          case None if deadline.isDefined && deadline.get.isOverdue =>
            p failure (new DeadlineExceededException)
          case None =>
            p failure (new TooManyRetriesException)
        }
        None
      } else {
        val success = try {
          val rez = if (deadline.isDefined) {
            Await.result(future(f()), deadline.get.timeLeft)
          } else {
            f()
          }
          Some(rez)
        } catch {
          case t: Throwable if !ignoreThrowable(t) =>
            blocking {
              val interval = backoff(retryCnt).toMillis
              Thread.sleep(interval)
            }
            recursiveRetry(retryCnt + 1, Some(t))(f)
          case t: Throwable =>
            p failure t
            None
        }
        success match {
          case Some(v) =>
            p success v
            Some(v)
          case None => None
        }
      }
    }

    def doBlock() = block

    future {
      recursiveRetry(0, None)(doBlock)
    }

    p.future
  }
}


val fail = Retry.retry(2) {
 "test".toInt
}                                              

Await.result(fail, 10 second) 

val rez = Retry.retry(2) {
 "test"
}
Await.result(rez, 10 second)