Sending Messages to Workers

Attila Rajmund Nohl attila.r.nohl@REDACTED
Mon Nov 15 22:07:02 CET 2021

Joseph Lloyd <josarlo84@REDACTED> ezt írta (időpont: 2021. nov. 15., H, 20:08):
> I am new to Erlang and using mailing lists, so please forgive my poor etiquette, and feel free to correct me.
> Background:
> I am prototyping a simple application using Erlang.  The application has a manager that reads messages from a socket (UDP in this case) and then sends the message (based on a destination byte) to a handler process.  There is a possibility of 2^n handler processes. The number is determined dynamically at run time based on user input.
> A handler process is created when the manager process receives a message to create the handler. create/3 is part of the handler module's API and is essentially a wrapper around handler_sup:start_child/2.  When the manager process receives a packet, it sends a message containing the packet to the appropriate handler process.  The manager process uses an ets table for mapping destinations to handler pids.
> I implemented the handlers as gen_servers and created a handler_sup that will restart the handler processes whenever they go down.
> Problem:
> If a handler process goes down, the destination/pid mapping in the manager module becomes invalid.  The handler supervisor will generate a new process, but the manager doesn't know the pid for the replacement process.
> Question:
> What is the proper way to design this in Erlang?  Do I put the destination/pid mapping in the handler_sup module and query that whenever the manager wants to send the message? Or does that violate supervisors only being supervisors paradigm?

One way is to have a process that monitors your workers and if it
receives a DOWN signal, removes the corresponding entry from the ETS
table. Of course, there are libraries that already implement this.

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