running Scala threads - multithreading

Question

I am an absolute beginner in Scala, but have this problem to solve.
So i have a list of parameters
itemList = List('abc', 'def', 'ghi','jkl','mno', 'pqr')
I have these 3 parameter queries
val q1 = "env='dev1'&id='123'&listitem='xyz'"
val q2 = "env='dev2'&id='1234'&listitem='xyz'"
val q3 = "env='dev3'&id='12345'&listitem='xyz'"
val report1 = getReport(q1)
val report2 = getReport(q2)
val report3 = getReport(q3)
So I am trying to loop through the list, replace the listitem parameter in q1, q2 and q3 with the listitem and then run the http request report for each item in the list.
Since each getReport request is asynchronous, i need to wait , and so i cannot go to the next item in the list, as it would be if i were to do a loop.
So i would like to start up 3 threads for each item in the list and then combine the 3 reports into 1 final one, or i could do it sequentially.
How would i go about doing it with 3 Threads for each item in the list?
This is my idea:
val reportToken = [ q1, q2,q3 ]
val listTasks = [ getReport(q1) , getReport(q2) , getReport(q3) ]
for (i <- 1 to 3) {
val thread = new Thread {
override def run {
listTasks (reportToken(i))
}
val concat += listTask(i)
}
thread.start
Thread.sleep(50)
}

Answer 1

You can wrap each of your tasks in a Future, apply map/recover to handle the successful/failed Futures, and use Future.sequence to transform the list of Futures into a Future of list. Here's a trivialized example:
import scala.concurrent.{Future, Await}
import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.duration.Duration
def getReport(q: String) = q match {
case "q2" => throw new Exception()
case q => s"got $q"
}
val reportToken = Seq("q1", "q2", "q3")
val listTasks = reportToken.map( q => Future{ getReport(q) } )
// listTasks: Seq[scala.concurrent.Future[String]] = ...
val f = Future.sequence(
listTasks.map(_.map(Some(_)).recover{case _ => None})
)
// f: scala.concurrent.Future[Seq[Option[String]]] = ...
Await.result(f, Duration.Inf)
// res1: Seq[Option[String]] = List(Some(got q1), None, Some(got q3))
For more details about Futures, here's a relevant Scala doc.

Answer 2

Assuming def getReport(str: String): Future[HttpResponse]
Future.sequence(itemList.map( item => {
for {
report1 <- getReport(q1.replace("xyz", item))
report2 <- getReport(q2.replace("xyz", item))
report3 <- getReport(q3.replace("xyz", item))
} yield {
(report1, report2, report3)
}
})).onComplete {
case Success(res) => // do something
case Failure(err) => // handle error
}