devil

Small proof-of-concept for a kind-of "daemon manager" scripted using lua

Config file

the config file is written using YAML

any kind of configuration possible should be documented in /devil.conf.example

Small Notes

• Daemons must be enabled explicitly in the config file
• Every daemon runs in its own thread
• This is just a draft/demo of what a friend had in mind, everything here may change at anytime.

Config

there are two "main" scopes

the global scope, which is from where default values may get taken (if needed) and the local scope, which is defined in a per-daemon basis, and may add or override (= take precendence over) the global scope

Daemon details

Every daemon's minimal configuration

• DAEMONS/name/daemon.conf

it has the following settings:

• entry_point (lua_file)

  defines the 'starting' point of the daemon.

  you probably want it to be init.lua, thus making the initial file loaded by Devil DAEMONS/name/init.lua

every daemon must register itself with the system, using daemon.register, it takes two parameters the first is the type of daemon, the second are options to that daemon type

daemon types:

• daemon.dummy

  options:

   Nothing
  

• daemon.busy_wait

  config_settings:

   wakeup: int
  
      time between checks to `condition`
      (may not be accurate if condition is expensive and takes too much time)
  

  options:

   condition:
  
       specifies the condition which needs to be valid for the event/action to run.
       iow, if it returns true, action is called
  
   action:
       see condition
  

• daemon.loop

  options:

   loop:
  
     function to keep running (it'll get called again the moment you quit)
  

availables APIs

config

• config.get_integer (string) : maybe int

  tries to gather setting from config, may return nil if the value is not found (or doesn't have the right type)

• config.get_string (string) : maybe string

  same as get_integer, but with string

chan

• chan.read (string) : lua_value

  gets a primitive value from the named channel (shared over all daemons) it'll always return a value, iow, it waits for it

• chan.write (string, lua_value) : unit

  sends a value over a named channel, non-locking

note: lua_value is basically a way to say the value is either an integer, a string, a boolean or nil

top-level

• sleep(n:int) : unit

  sleep for N seconds

• print(string) : unit

• throw_exception(err:string) : 'a

  (this function basically 'crashes' the current thread)