[erlang-questions] Distributed Applications: Stop Before Start?

Vance Shipley <>
Wed Mar 28 13:40:31 CEST 2012


On Tue, Mar 27, 2012 at 08:15:17AM -0700, Ulf Wiger wrote:
}  Ok, then one thing that can be done is to create a 'wrapper application'
}  that starts snmp as an included app.
}  
}  Your start function would have to call the appropriate function in snmp,
}  since included apps are not automatically started by OTP.
}  
}  We used to do this at AXD 301, in order to ensure that applications using
}  snmp did a takeover in synch with snmp itself. 

Ulf,

A couple things about this concern me;

	/Users/otpuser/lib/erlang/doc/design_principles/included_applications.html 

  "the top supervisor of the included application must be started by a
   supervisor in the including application"

The snmp:start/0,1 snmp:start_agent/0,1 and application:start/1,2 functions
don't behave as a supervisor requires.  There is an appropriate start
function in snmpa_supervisor:start_master_sup/1 however then the snmp 
application is not listed with application:which_applications/0.

  "This means that when running, an included application is in fact part
   of the primary application and a process in an included application
   will consider itself belonging to the primary application."

So if a process in the snmp application would call application:get_all_env/0
it wouldn't get what it expects.  It does look like all the calls to the
application module do include the application name (snmp) however.


-- 
	-Vance



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