Play: Create own Execution Context

import java.util.concurrent.Executors
import javax.inject.Inject
import scala.concurrent.ExecutionContext
import akka.actor.ActorSystem
import play.api.libs.concurrent.CustomExecutionContext

// way1: extend CustomExecutionContext and pass the name of your Akka dispatcher
class MyExecutionContext @Inject()(as: ActorSystem) extends CustomExecutionContext(as, "my-context")

// way2: use Akka lookup method (in fact 100% the same as way1)
class Aaa @Inject()(as: ActorSystem) {
  implicit val ec: ExecutionContext = as.dispatchers.lookup("my-context")
}

// way3: use standard Java Library: call "fromExecutor" or "fromExecutorService" methods of ExecutionContext
class Bbb {
  implicit val ec: ExecutionContext = ExecutionContext.fromExecutor(Executors.newFixedThreadPool(10))
}



// application.conf:
my-context {
  for-join-executor {
    # The parallelism factor is used to determine thread pool size using the
    # following formula: ceil(available processors * factor). Resulting size
    # is then bounded by the parallelism-min and parallelism-max values.
    parallelism-min = 8
    parallelism-max = 16
    parallelism-factor = 2.0
    task-peeking-mode = "FIFO"
  }
}