Call Py_FinalizeEx() when process exits

ext/pycall/libpython.c

@@ -89,6 +89,7 @@ pycall_init_libpython_api_table(VALUE libpython_handle)
   INIT_API_TABLE_ENTRY(PyUnicode_Type, required);
 
   INIT_API_TABLE_ENTRY(Py_InitializeEx, required);
+  INIT_API_TABLE_ENTRY(Py_FinalizeEx, required);
   INIT_API_TABLE_ENTRY(Py_IsInitialized, required);
   INIT_API_TABLE_ENTRY(Py_GetVersion, required);
 

ext/pycall/pycall.c

@@ -681,6 +681,15 @@ pycall_libpython_api_PyList_GetItem(VALUE mod, VALUE pyptr, VALUE idx)
   return pycall_pyptr_new(pyobj_item);
 }
 
+static VALUE
+pycall_libpython_api_Py_FinalizeEx(VALUE mod)
+{
+  assert(Py_API(Py_IsInitialized()));
+
+  return Py_API(Py_FinalizeEx)();
+}
+
+
 /* ==== PyCall::Helpers ==== */
 
 static VALUE
@@ -2372,6 +2381,7 @@ Init_pycall(void)
   rb_define_module_function(mAPI, "PyObject_Dir", pycall_libpython_api_PyObject_Dir, 1);
   rb_define_module_function(mAPI, "PyList_Size", pycall_libpython_api_PyList_Size, 1);
   rb_define_module_function(mAPI, "PyList_GetItem", pycall_libpython_api_PyList_GetItem, 2);
+  rb_define_module_function(mAPI, "Py_FinalizeEx", pycall_libpython_api_Py_FinalizeEx, 0);
 
   /* PyCall::LibPython::Helpers */
 

ext/pycall/pycall_internal.h

@@ -565,6 +565,7 @@ typedef struct {
   PyObject *PyExc_TypeError;
 
   void (* Py_InitializeEx)(int);
+  int (* Py_FinalizeEx)(void);
   int (* Py_IsInitialized)();
   char const * (* Py_GetVersion)();
 

lib/pycall/init.rb

@@ -45,6 +45,17 @@ class << LibPython
     require 'pycall/slice'
     const_set(:PYTHON_VERSION, LibPython::PYTHON_VERSION)
     const_set(:PYTHON_DESCRIPTION, LibPython::PYTHON_DESCRIPTION)
+
+    @init_thread_id = Thread.current.object_id
+    at_exit do
+      # Finalize is only safe to call if we're on the same thread that initialized PyCall
+      finalize if Thread.current.object_id == @init_thread_id
+    end
+
     true
   end
+
+  def self.finalize
+    LibPython::API.Py_FinalizeEx()
+  end
 end

pycall_hangs_main_thread.rb

@@ -0,0 +1,14 @@
+#!/usr/bin/env ruby
+
+side_thread = Thread.new do
+  require 'pycall'
+  PyCall.import_module('sys')
+  PyCall.import_module('pandas')
+
+  PyCall.finalize # if this line is commented out, the process will hang on exit
+  puts "side thread: exiting"
+end
+side_thread.join
+
+puts "main thread: exiting"
+#=> process exits!

test.sh

@@ -0,0 +1,5 @@
+#!/bin/bash
+
+set -ex
+
+bundle exec ruby -I ext/pycall pycall_hangs_main_thread.rb 2> /dev/null