parMapN that finishes even when one program encounters an error

Question

Using parMapN, multiple IOs can be executed in parallel, like this:

import cats.implicits._
import cats.effect.{ContextShift, IO}
import scala.concurrent.ExecutionContext

implicit val cs: ContextShift[IO] = IO.contextShift(ExecutionContext.global)

val ioA = IO(for(i <- 1 to 100) { println(s"A$i"); Thread.sleep(100) })
val ioB = IO(for(i <- 1 to 100) { println(s"B$i"); Thread.sleep(100) })
val ioC = IO(for(i <- 1 to 100) { println(s"C$i"); Thread.sleep(100) })

val program = (ioA, ioB, ioC).parMapN { (_, _, _) => () }

program.unsafeRunSync()

Sample output:

A1
C1
B1
A2
C2
B2
A3
C3
B3
A4
C4
B4
A5
B5
C5
A6
B6
C6
A7
B7
C7
A8
...

According to the documentation, unfinished tasks get cancelled if any of the IOs completes with a failure. What is the best way of changing this mechanism, so that all IOs are finishing anyway?

In my case some of the IOs do not return anything (IO[Unit]) and I still want to make sure everything runs until it is finished or encounters an error.

Answer 1

Well I found one possible answer shortly after posting my question. Not sure if it is the best way to handle this, but defining my IOs like this works for me:

val ioA = IO(for(i <- 1 to 100) { println(s"A$i"); Thread.sleep(100) }).attempt
val ioB = IO(for(i <- 1 to 100) { println(s"B$i"); Thread.sleep(100) }).attempt
val ioC = IO(for(i <- 1 to 100) { println(s"C$i"); Thread.sleep(100) }).attempt