Erlang's process group module allows adding arbitrary PIDs to a group,
which can be used for things like
PubSub: https://www.erlang.org/doc/man/pg.html
Registry's register function currently always registers the current
process; you cannot register an arbitrary
process: https://hexdocs.pm/elixir/1.14.5/Registry.html#register/3
However, there are ways to work around this with Registry; see attached
Livebook markdown for an example.
I propose new functions:
- Registry.register/4
- register(pid, registry, key, value)
- Registry.unregister/3
- unregister(pid, registry, key)
- Registry.unregister_match/5
- unregister_match(pid, registry, key, pattern, guards \\ [])
- Registry.update_value/4
- update_value(pid, registry, key, callback)
Another (potentially simpler) option might be to have the pid argument be
at the end and make it default to self().
Thoughts? 😄
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# Registry
## Register arbitrary PID
```elixir
defmodule RegistryTest do
def init() do
Registry.start_link(
keys: :duplicate,
name: Registry.PubSubTest,
partitions: System.schedulers_online()
)
end
def subscribe_pid(pid) do
# The third argument of `register` allows any arbitrary data, including a
pid!
{:ok, _} = Registry.register(Registry.PubSubTest, "hello", {pid, :other,
"data"})
end
def send_message(message) do
Registry.dispatch(Registry.PubSubTest, "hello", fn entries ->
# Then you can just pull the pid out as the "subscriber" pid and send to
it!
for {_, {subscriber_pid, _other, _data}} <- entries, do:
send(subscriber_pid, message)
end)
:ok
end
end
pid1 =
spawn(fn ->
receive do
:hello -> IO.puts("world")
end
end)
pid2 =
spawn(fn ->
receive do
:hello -> IO.puts("ocean")
end
end)
pid3 =
spawn(fn ->
receive do
:hello -> IO.puts("sky")
end
end)
RegistryTest.init()
RegistryTest.subscribe_pid(pid1)
RegistryTest.subscribe_pid(pid2)
RegistryTest.subscribe_pid(pid3)
RegistryTest.send_message(:hello)
```
<!-- livebook:{"output":true} -->
```
world
ocean
sky
```
<!-- livebook:{"output":true} -->
```
:ok
```
