a clean way for an actor to restart itself

[dougcooper]

i might just be ignorant and abusing the design pattern, but i was trying to leverage the retry behavior of the library and was manually calling pre_restart from a handle method which results in a deadlock. instead im now creating a task on pre_start and then telling myself from the task to respawn the task such that pre_start only gets called once in the lifetime of the actor.

[fdeantoni]

Currently the restart only works to handle startup problems. It does not really work for handling message failures. This definitely needs to be addressed though!