Develop Supervisors.jl

[pbayer]

Basic supervision must be built right into Actors. This is described in issue #16 .

Supervision tree

The possibility to define a supervision tree in a module with actors as callback functions has to be implemented in a separate library. This will allow a user to easily build multilevel supervision trees.

• create Supervisors.jl,
• specify Supervisors,
• develop Supervisors.

[pbayer]

System Actors

Like in Erlang/Elixir a :system actor traps Exit signals and does not propagate them further. Only if a :system actors fails, it sends Exit signals to connected actors.

If an actor fails, the exception and a stack trace are preserved in its link/channel. Therefore a :system actor needs to store the link to the failed actor to be able to preserve all necessary information about the failure.

A failing actor therefore sends the exception and its own link to its connections, which forward the Exit signal until eventually a :system actor gets it. The :system actor reports the exception and stores the link to the failed actor in its task_local_storage. The diagnostic information can be retrieved from the system actor via diag.

Thus every :default actor can become a :system actor and does then have this functionality.

There is one restriction to this logic: actors extending the Actors protocol like :genserver or :guard cannot become :system actors without loosing their functionality.

PS: Monitors are likewise :system actors, but they don't have links to their monitored actors, so the don't send them Exit signals if they fail.