How many threads does Akka use?

Question

As i know, Akka uses several threads to serve all actors in ActorSystem. I would like to programmatically check, how many threads Akka uses. But i don't want to use profilers or jConsole.

Answer 1

An estimate can be made from the configuration since it is usually a factor of the number of cores on the host.

An exact number would come from the thread pools used under the hood. The first issue is getting a handle to the underlying pool from the dispatchers. Note that there can be multiple dispatchers/executors.

The most common is the fork join pool. You can call getActiveThreadCount on the pool to find the number of threads in use. If java's ForkJoinPool is being used, you can call getPoolSize.

Answer 2

You can traverse the thread group tree to find the thread groups created by akka, and get the active thread counts.

object ThreadGroupUtils {

  def getThreadGroup: ThreadGroup = Thread.currentThread.getThreadGroup

  def findAncestor(current: ThreadGroup)(isTarget: ThreadGroup => Boolean): Option[ThreadGroup] = {
    Option(current.getParent) match {
      case None =>
        None
      case opt @ Some(parent) if isTarget(parent) =>
        opt
      case Some(parent) =>
        findAncestor(parent)(isTarget)
    }
  }

  def root = findAncestor(getThreadGroup)(_.getParent == null).get

  def main = findAncestor(getThreadGroup)(_.getName == "main").get

  def getSubGroups(parent: ThreadGroup): Seq[ThreadGroup] = {
    val subgroups = new Array[ThreadGroup](parent.activeGroupCount)
    val copied = parent.enumerate(subgroups)
    subgroups.iterator.take(copied).toSeq
  }

  def printThreadGroups(group: ThreadGroup = root, indent: String = ""): Unit = {
    val subgroups =getSubGroups(group)
    println(s"${indent}${group.getName}: ${subgroups.size} subgroups, ${group.activeCount} threads")
    subgroups.foreach(printThreadGroups(_, indent + "    "))
  }
}

ThreadGroupUtils.printThreadGroups()