You can use GenServer & send_after for this, not complex at all, and still allows for other events to be received & handled asynchronously should that ever be needed.
sribe
kexoth
Correct me if I’m wrong, but some libraries require creation of non-OTP processes, such as HTTPoison’s & HTTPotion’s support for streaming.
I was searching for a way to create an OTP-like process which will function well even if I make a receive loop & I found here @fishcakez’s Core library which he actually never used, but I will 
EDIT: Unfortunately the library is quite outdated, so I ended up using Task. 
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Crowdhailer
Creator of Raxx
I was going through this slide show. Does anyone know if there is a video for this talk? Also do people agree with the usecase that a supervisor + some state management is a good example for a special process.
I’m thinking of using a special process to solve this issue here https://stackoverflow.com/questions/44663817/how-to-reference-previously-started-processes-in-an-elixir-supervisor/44663920
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sasajuric
Author of Elixir In Action
You could also use a GenServer for that.
You could use Supervisor.which_children in the second child to ask the parent about the children, and then find the pid of the sibling you’re interested in.
However, you can’t do this in init/1, since you’ll deadlock, so you need to postpone this for after init. The second child can send itself a message (e.g. :post_init), and then in the corresponding handle_info ask its parent about the children, find the desired sibling, and store the pid in its own state. It’s a bit tricky, but does the job.
Make sure to use rest_for_one or one_for_all supervision strategy, or otherwise you might end up with a dangling reference to a non-existing process.
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Crowdhailer
Creator of Raxx
Do all OTP processes have a reference to their parent? if so then that is something I have missed and sounds a helpful solution. Although It still seams messy to have a process know about the structure of a supervision tree it is in. In essence I am having to change the structure of a child after adding it to a supervision tree
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sasajuric
Author of Elixir In Action
There is an undocumented :$ancestors procdict key:
iex> Process.get(:"$ancestors")
[#PID<0.50.0>]
Whether you want to rely on that is another matter 
If you want to be more explicit, you can pass the pid of the parent to the child from supervisor’s init/1.
I agree it’s messy, but I also think it’s fine in those rare cases where siblings are tightly coupled. For other cases, I’d use Registry to discover processes in the system. I talked about this last year at ElixirConf EU. You can find the video here. There was no Registry back then, so I used gproc as the registry, but other than that, I believe the talk is still up to date.
Not sure I understand what you mean by this.
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dom
Regarding:
I’m not sure registry offers any value, I would still have to come up with a random key in the registry to avoid clashes required to start the top level supervisor more than once
make_ref() returns a nice unique key.
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Azolo
Yes. It’s matched against in the receive loop. When a OTP special process parent exits then the process must exit.
This is a little different than a parent in a way I don’t fully understand and the little I can understand, I can’t explain. But I’ll try anyway!
In iex when I use import_file to import an .exs file and in that file I start a linked process there’s an extra pid in $ancestors but I’m still linked to the iex process.
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Azolo
Task actually only meets one of the requirements for a special process.
Be started in a way that makes the process fit into a supervision tree
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