If you have actors depending on each other, you may want them to exit together if one of them terminates. Therefore you can connect them as peers. Then an actor will send an Exit message to its connected actors. Those propagate the Exit message (caused by a failure, stop or exit!) to their connected actors and then terminate

  • if the exit reason is other than :normal,
  • and if they are not :sticky.

With trapExit an actor can be made :sticky. When it then receives an Exit message with a reason other than :normal, it will

  • not propagate it and not terminate but
  • give a warning about it and
  • store a link to the failed actor.

Connections between actors are always bidirectional and can be disconnected. You can build a chain or network of connected actors that depend on each other and exit together. A :sticky actor operates as a firewall among connected actors.


Assume in an actor system A1-A3-A7-A9-A4 are connected, A3 is a :sticky actor and A9 fails. Before it terminates, it sends an Exit message to A4 and A7. A7 propagates it further to A3. A9, A4 and A7 die together. A3 gives a warning about the failure and saves the link to the failed actor A9. A3 does not propagate the Exit to A1. Both A1 and A3 stay connected and continue to operate. The other actors are separate and are not affected by the failure.

See a Julia script illustrating the above system in the How-to section.