Prevent cffi from unloading Go shared library

Author: b-long

.github/workflows/ci.yml

@@ -109,6 +109,8 @@ jobs:
     runs-on: ${{ matrix.platform }}
     env:
       GOPY_BACKEND: cffi
+      # print the python stack if the process crashes, e.g. at exit
+      PYTHONFAULTHANDLER: 1
     steps:
     - name: Checkout code
       uses: actions/checkout@v4

bind/cffi_build.py

@@ -116,14 +116,20 @@ def wrapper(name, ret, params, exported):
 MODULE_HEAD = '''# python bindings for package @NAME@ using cffi.
 # File is generated by gopy version @VERSION@. Do not edit.
 import builtins
+import ctypes
 import os
 from operator import index as _index
 
 import cffi
 
 _ffi = cffi.FFI()
 _ffi.cdef(@CDEFS@)
-_lib = _ffi.dlopen(os.path.join(os.path.dirname(os.path.abspath(__file__)), "@NAME@_go@LIBEXT@"))
+_path = os.path.join(os.path.dirname(os.path.abspath(__file__)), "@NAME@_go@LIBEXT@")
+_lib = _ffi.dlopen(_path)
+# Go cannot unload its runtime.  cffi unloads _lib at interpreter shutdown but
+# ctypes never unloads, so this second handle keeps the library loaded until
+# the process exits, as for an extension module.
+_pin = ctypes.CDLL(_path)
 
 
 def _enc(s, argn):