Scala program using futures is not terminating - scala

Question

I am trying to learn concurrency in Scala and using Scala futures to generate a dataset with random string. I want to create an application which should generate a file with any number of records and it should be scalable.
Code:
import java.util.concurrent.{ExecutorService, Executors}
import scala.util.{Failure, Random, Success}
import scala.concurrent.duration._
object datacreator {
implicit val ec: ExecutionContext = new ExecutionContext {
val threadPool: ExecutorService = Executors.newFixedThreadPool(4)
def execute(runnable: Runnable) {
threadPool.submit(runnable)
}
def reportFailure(t: Throwable) {}
}
def getRecord : String = {
"Random string"
}
def main(args: Array[String]): Unit = {
val filename = args(0)
val number_of_records = args(1)
val file_Object = new FileWriter(filename, true)
val data: Future[Iterable[String]] = Future {
for (i <- 1 to number_of_records.toInt)
yield getRecord
}
val result = data.map{
result => result.foreach(record => file_Object.write(record))
}
result.onComplete{
case Success(value) => {
println("Success")
file_Object.close()
}
case Failure(e) => e.printStackTrace()
}
}
}
I am facing the following issues:
When I am running the program using SBT it is writing results to the file but not terminating as going in infinite mode.
[info] Loading project definition from /Users/cw0155/PersonalProjects/datagen/project
[info] Loading settings for project datagen from build.sbt ...
[info] Set current project to datagenerator (in build file:/Users/cw0155/PersonalProjects/datagen/)
[info] running com.generator.DataGenerator xyz.csv 100
Success
| => datagen / Compile / runMain 255s
When I am running the program using Jar as:
scala -cp target/scala-2.13/datagenerator_2.13-0.1.jar com.generator.DataGenerator "pqr.csv" "1000"
It is waiting infinite time and not writing to the file.
Any help is much appreciated :)

Answer 1

Try this version
bar.scala
import scala.concurrent.{Await, Future, ExecutionContext}
import scala.concurrent.duration._
import scala.util.{Success, Failure}
import ExecutionContext.Implicits.global
import java.io.FileWriter
object bar {
def getRecord: String = "Random string\n"
def main(args: Array[String]): Unit = {
val filename = args(0)
val number_of_records = args(1)
val data: Future[Iterable[String]] = Future {
for (i <- 1 to number_of_records.toInt)
yield getRecord
}
val file_Object = new FileWriter(filename, true)
val result = data.map( r => r.foreach(record => file_Object.write(record)) )
result.onComplete {
case Success(value) =>
println("Success")
file_Object.close()
case Failure(e) =>
e.printStackTrace()
}
Await.result( result, 10.second )
}
}
Your original version gave me the expected output when I ran it like so
bash-3.2$ scala bar.scala /dev/fd/1 10
Success
Random string
Random string
Random string
Random string
Random string
Random string
Random string
Random string
Random string
Random string
However without the Await.result your program can exit before the future finishes.