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defmodule Limiter do
@ets __MODULE__.ETS
def new(name, max_running, max_waiting) do
name = atom_name(name)
:persistent_term.put(name, {max_running, max_waiting})
:ets.new(name, [:public, :named_table])
:ok
end
def limit(name, fun) do
{max_running, max_waiting} = :persistent_term.get(atom_name(name))
max = max_running + max_waiting
counter = inc(name)
cond do
counter <= max_running ->
fun.()
counter > max ->
{:error, :overload}
counter > max_running ->
wait(name, fun)
end
after
dec(name)
end
defp wait(name, fun) do
Process.sleep(150)
dec(name)
limit(name, fun)
end
defp inc(name) do
name = atom_name(name)
:ets.update_counter(name, name, {2, 1}, {name, 0})
end
def dec(name) do
name = atom_name(name)
:ets.update_counter(name, name, {2, -1}, {name, 0})
end
defp atom_name(suffix), do: Module.concat(@ets, suffix)
end
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