per actor policy

[basiliscos]

The various actor-spawning pieces are scattered across API:

1. init-timeout is provided in create_actor
2. shutdown-timeout is configure in per-actor
3. init-failure and shutdown-failure triggers are hard-coded in supervisor.

The idea is to have an per-actor dedicated class (transferred per actor constructor) with the appropriate settings:

• initi-timeout
• shutdown-timeout
• init-attempts
• init-failure-behaviour: shutdown, crash, custom
• shutdown-attempts
• shutdown-failure-behaviour: crash, custom