@spec ensure_started(atom(), (-> {:ok, pid()} | {:error, {:already_started, pid()}})) ::
  :ok

Ensures a named process is running. Starts it via start_fun if not found.

start_fun is a zero-arity function that starts the process UNLINKED (GenServer.start/3, Agent.start/2) and registers it under name. It must return {:ok, pid} or {:error, {:already_started, pid}}.

The process is started unlinked because the first caller is often a rendering process, a session process or an ExUnit test process. With start_link, that caller's exit took the singleton, and all of its state, with it, and a crash in the singleton killed whichever process happened to call first.

Two callers can both find no process and both run start_fun. The loser gets {:error, {:already_started, pid}}, which counts as started.

Examples

ensure_started(MyServer, fn ->
  GenServer.start(MyServer, [], name: MyServer)
end)

Standard handler for getting specific state fields.

Standard handler for getting metrics from state.

Standard handler for getting state information.

Standard handler for getting status information.

Standard handler for resetting metrics.

Standard handler for updating configuration.

Utility to increment a metric counter.

Initialize default state with common fields.

@spec split_server_opts(keyword() | map() | term()) :: {keyword(), keyword() | term()}

Splits a keyword list into GenServer server options and init args.

Server options (:name, :timeout, :debug, :spawn_opt) are separated from the remaining application-specific options.

Examples

iex> split_server_opts(name: MyServer, timeout: 5000, foo: :bar)
{[name: MyServer, timeout: 5000], [foo: :bar]}

iex> split_server_opts(%{name: MyServer})
{[name: MyServer], []}

Utility to update a metric value.