Fix multiple concurrent calls to install_and_run/2 (#58) (#59)

lib/esbuild.ex

@@ -89,7 +89,7 @@ defmodule Esbuild do
         :ok
     end
 
-    Supervisor.start_link([], strategy: :one_for_one)
+    Supervisor.start_link([], strategy: :one_for_one, name: __MODULE__.Supervisor)
   end
 
   @doc false
@@ -182,15 +182,30 @@ defmodule Esbuild do
     |> elem(1)
   end
 
+  defp start_unique_install_worker() do
+    ref =
+      __MODULE__.Supervisor
+      |> Supervisor.start_child(
+        Supervisor.child_spec({Task, &install/0}, restart: :transient, id: __MODULE__.Installer)
+      )
+      |> case do
+        {:ok, pid} -> pid
+        {:error, {:already_started, pid}} -> pid
+      end
+      |> Process.monitor()
+
+    receive do
+      {:DOWN, ^ref, _, _, _} -> :ok
+    end
+  end
+
   @doc """
   Installs, if not available, and then runs `esbuild`.
 
   Returns the same as `run/2`.
   """
   def install_and_run(profile, args) do
-    unless File.exists?(bin_path()) do
-      install()
-    end
+    File.exists?(bin_path()) || start_unique_install_worker()
 
     run(profile, args)
   end

test/esbuild_test.exs

@@ -32,4 +32,29 @@ defmodule EsbuildTest do
              assert Esbuild.run(:default, ["--version"]) == 0
            end) =~ @version
   end
+
+  test "install and run multiple concurrently" do
+    bin_path = Esbuild.bin_path()
+
+    assert :ok = File.exists?(bin_path) && File.rm!(bin_path)
+
+    results =
+      [:extra1, :extra2, :extra3]
+      |> Enum.map(fn profile ->
+        Application.put_env(:esbuild, profile, args: ["--version"])
+
+        Task.async(fn ->
+          ret_code = Esbuild.install_and_run(profile, [])
+          # Let the first finished task set the binary file to read and execute only,
+          # so that the others will fail if they try to overwrite it.
+          File.chmod!(bin_path, 0o500)
+          ret_code == 0
+        end)
+      end)
+      |> Task.await_many(:infinity)
+
+    File.chmod!(bin_path, 0o700)
+
+    assert results |> Enum.all?()
+  end
 end