ExReg

A simple process name registry using :pg:

• Depends on the built-in Erlang's :pg app
• Can be used with :via tuples for naming GenServers, Agents, etc.
• Accepts any valid erlang term as process names.
• Supports several processses with the same name as long as they are not in the same node. Always picks the node closest to the process that called the function.

Small example

Let's say we define the following Agent for keeping a counter:

defmodule Counter do
  use Agent

  def start_link(options \\ []) do
    Agent.start_link(fn -> 0 end, options)
  end

  def increment(counter) do
    Agent.get_and_update(counter, &{&1, &1 + 1})
  end
end

We can now start it using ExReg as name registry:

iex(1)> name = {:via, ExReg, {"metric", :my_counter}}
iex(2)> Counter.start_link(name: name)
{:ok, #PID<0.42.0>}
iex(3)> Counter.increment(name)
1
iex(4)> Counter.increment(name)
2

Distributed systems

In a distributed environment, there are several things to notice:

• ExReg allows several processes to share the same name as long as they are not in the same Erlang node.

• When starting processes a process locally or sending messages exclusively to a local process:

  • The name should match the type {:local, term()} e.g:

    Counter.start_link({:via, ExReg, {:local, {"metric", :my_counter}}})

  • The function ExReg.local({"metric", :my_counter}) can also be used to generate the local via tuple.

• When sending messages to a named process, no matter its location:

  • The name should be the term itself or {:global, term()} e.g:

    Counter.increment({:via, ExReg, {"metric", :my_counter}})

  • The function ExReg.global({"metric", :my_counter}) can also be used to generate the global via tuple.

Installation

Add ExReg to your list of dependencies in mix.exs:

def deps do
  [{:exreg, "~> 1.0"}]
end

Requires OTP 24 or more.

Author

Alexander de Sousa

License

ExReg is released under the MIT License. See the LICENSE file for further details.