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

[Vance Shipley]

My current problem is that it's not my application, it's OTP's. It's snmp. I tried using rpc:call/4 in my application's start/2 callback to call application:permit/2 but that just deadlocked.


Ulf Wiger <ulf@REDACTED> wrote:

>
>In the start_phase() call, you can make a gen_server call to the foo_app
>instance running on a and ask it to close its connections.
>
>If that's what you're already doing, perhaps I misunderstood the question?
>
>BR,
>Ulf W
>
>On 27 Mar 2012, at 07:01, Vance Shipley wrote:
>
>> Is there a clever way to get "stop first" semantics out of dist_ac?
>> 
>> A distributed application in OTP may migrate from a failed node
>> to another and it may migrate back when the original node returns.
>> 
>> You can initiate a transfer with application:permit(foo, false).
>> The order of the callbacks is:
>> 
>>   a@REDACTED                  b@REDACTED
>>   ---------------------   -------------------
>>                           foo_app:start({takeover, a@REDACTED}, [])
>>                           foo_app:start_phase(phase1, {takeover, a@REDACTED}, [])
>>                           foo_app:start_phase(phase2, {takeover, a@REDACTED}, [])
>>   foo_app:prep_stop([])
>>   foo_app:stop([])
>> 
>> Only the start/2 and stop/1 callbacks are required, the others are optional.
>> 
>> I'm currently trying to distribute OTP's snmp application between two
>> nodes on the same host but it fails in the situation above because it
>> tries to bind to the address already in use:
>> 
>>     ** Configuration error: failed starting net-if: 
>>     {udp_open,161,eaddrinuse}
>> 
>> So in this case I'd like to have the application stopped on the old
>> node before it is started on the new node.
>> 
>> -- 
>> 	-Vance
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>