[erlang-questions] Sharing child processes across supervisors

[Garrett Smith]

Thanks! This is straight forward and cleans up the supervisory
hierarchy that I was using.

On Fri, Mar 5, 2010 at 4:16 PM, Jayson Vantuyl <kagato@REDACTED> wrote:
> Have the gen_server link to the other gen_servers (or vice-versa).  Then when one fails, the other dies, and the supervisors in the remote apps take care of it.  It might require some synchronization around the restarting (or maybe a delay in somebody's init), but I've done this sort of thing a lot.
>
> On Mar 5, 2010, at 2:04 PM, Garrett Smith wrote:
>
>> I have a gen_server that maintains a connection to something. I'd like
>> to have a single such gen_server per release (VM instance).
>>
>> I generally run this server under a one_for_all supervisor -- anyone
>> who depends on that connection is also under this supervisor. When the
>> connection fails, the dependencies are all restarted.
>>
>> If I have multiple OTP applications that share this connection, each
>> application will want to supervise the gen_server. I could merge the
>> supervisory trees of the multiple applications into one, but this
>> doesn't feel right at all - I want to keep the applications as
>> separate as possible.
>>
>> I'm tempted to modify the start_link of the connection to look like this:
>>
>>  start_link() ->
>>    case gen_server:start_link({local, ?SERVER}, ?MODULE, [], []) of
>>      {ok, Pid} -> {ok, Pid};
>>      {already_started, Pid} -> {ok, Pid};
>>      Other -> Other
>>    end.
>>
>> My thinking is that this would fake out supervisors that subsequently
>> tried to start the connection, causing them to link and supervisor as
>> if they actually started it. Naively, it would seem that a connection
>> failure would be detected by all of the linked supervisors, triggering
>> the expected cascades. One of the applications would end up restarting
>> the connection and the rest would link per the "fake out" above.
>>
>> Would this approach be bad for any reason? Is there a better or
>> standard way of getting supervision across applications?
>>
>> Garrett
>>
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>
> --
> Jayson Vantuyl
> kagato@REDACTED
>
>
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