1 files changed, 47 insertions, 0 deletions
diff --git a/lib/limiter.ex b/lib/limiter.ex
new file mode 100644
index 0000000..84c601c
--- /dev/null
+++ b/lib/limiter.ex
@@ -0,0 +1,47 @@
+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