CPU-bound tasks for experimenting in the Scala REPL

CPUboundTasks.scala

// a CPU-intensive task
def isPrime(i: Long): Boolean =
  if i == 2 then return true
  if i < 2 || i % 2 == 0 then return false
  var k = 3L
  val half = i / 2
  while k <= half do
    if i % k == 0 then return false
    k += 2
  true

// running two tasks sequentially
// about 18 seconds on a MacBook Air
val t0 = System.currentTimeMillis
isPrime(1500450271)
isPrime(1500450271)
System.currentTimeMillis - t0

// running two tasks concurrently
// about 12 seconds on a MacBook Air
val p1 = new java.lang.Thread:
  override def run() = isPrime(1500450271)
val p2 = new java.lang.Thread:
  override def run() = isPrime(1500450271)
val t1 = System.currentTimeMillis
p1.start()
p2.start()
p1.join()
p2.join()
System.currentTimeMillis - t1