From ea29718068c5339077d0900a57eb395917545703 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jonatan=20K=C5=82osko?= <jonatanklosko@gmail.com>
Date: Mon, 3 Mar 2025 18:09:38 +0100
Subject: [PATCH] Fix waiting on child processes blocking indefinitely (#15)

---
 lib/pythonx/application.ex | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/lib/pythonx/application.ex b/lib/pythonx/application.ex
index a4b8053..1be6aa8 100644
--- a/lib/pythonx/application.ex
+++ b/lib/pythonx/application.ex
@@ -5,6 +5,8 @@ defmodule Pythonx.Application do
 
   @impl true
   def start(_type, _args) do
+    enable_sigchld()
+
     children = [
       Pythonx.Janitor
     ]
@@ -26,4 +28,16 @@ defmodule Pythonx.Application do
   else
     defp maybe_uv_init(), do: :noop
   end
+
+  defp enable_sigchld() do
+    # Some APIs in Python, such as subprocess.run, wait for a child
+    # OS process to finish. On Unix, this relies on `waitpid` C API,
+    # which does not work properly if SIGCHLD is ignored, resulting
+    # in infinite waiting. ERTS ignores the signal by default, so we
+    # explicitly restore the default handler.
+    case :os.type() do
+      {:win32, _osname} -> :ok
+      {:unix, _osname} -> :os.set_signal(:sigchld, :default)
+    end
+  end
 end