Avoid segfault when OSM object constructer is interrupted

lib/osm_base_objects.h

@@ -2,7 +2,7 @@
  *
  * This file is part of pyosmium. (https://osmcode.org/pyosmium/)
  *
- * Copyright (C) 2024 Sarah Hoffmann <lonvia@denofr.de> and others.
+ * Copyright (C) 2026 Sarah Hoffmann <lonvia@denofr.de> and others.
  * For a full list of authors see the git log.
  */
 #ifndef PYOSMIUM_OSM_BASE_OBJECTS_HPP
@@ -73,7 +73,6 @@ class PyOSMObject
     pybind11::object get_or_create_python_object()
     {
         if (!m_valid) {
-            m_valid = true;
             if constexpr (std::is_same_v<T, osmium::Node>) {
                 m_pyobj = pybind11::module_::import("osmium.osm.types").attr("Node")(COSMNode{m_obj});
             } else if constexpr (std::is_same_v<T, osmium::Way>) {
@@ -85,6 +84,7 @@ class PyOSMObject
             } else if constexpr (std::is_same_v<T, osmium::Changeset>) {
                 m_pyobj = pybind11::module_::import("osmium.osm.types").attr("Changeset")(COSMChangeset{m_obj});
             }
+            m_valid = true;
         }
 
         return m_pyobj;

test/test_constructor_interruption.py

@@ -0,0 +1,54 @@
+# SPDX-License-Identifier: BSD-2-Clause
+#
+# This file is part of pyosmium. (https://osmcode.org/pyosmium/)
+# Copyright (C) 2026 Sarah Hoffmann <lonvia@denofr.de> and others.
+# For a full list of authors see the git log.
+import multiprocessing
+import sys
+
+import pytest
+import osmium
+
+
+def run_interrupted_read(pipe, object_type, opl, exception_type):
+    constructor = object_type.__init__.__code__
+
+    def fail_constructor(frame, event, arg):
+        if event == 'call' and frame.f_code is constructor:
+            sys.settrace(None)
+            raise exception_type('injected constructor failure')
+        return fail_constructor
+
+    sys.settrace(fail_constructor)
+    try:
+        list(osmium.FileProcessor(osmium.io.FileBuffer(opl.encode('utf-8'), 'opl')))
+    except exception_type:
+        sys.settrace(None)
+        pipe.send(str(exception_type))
+    else:
+        pipe.send('constructor was not reached')
+
+
+@pytest.mark.thread_unsafe
+@pytest.mark.parametrize('object_type', [osmium.osm.Node, osmium.osm.Way, osmium.osm.Relation])
+@pytest.mark.parametrize('exception', [KeyboardInterrupt, MemoryError, RuntimeError])
+def test_constructor_exception_does_not_crash_cleanup(to_opl, object_type, exception):
+    data = to_opl("""\
+        n1 x5 y5
+        w1 Nn1,n2
+        r1 Mn1@
+    """)
+
+    parent_conn, child_conn = multiprocessing.Pipe()
+    ctx = multiprocessing.get_context('spawn')
+    p = ctx.Process(target=run_interrupted_read,
+                    args=[child_conn, object_type, data, exception])
+    p.start()
+
+    assert parent_conn.poll(2)
+    assert parent_conn.recv() == str(exception)
+
+    p.join(2)
+
+    assert p.exitcode == 0, f"Segmentation fault ({-p.exitcode})" if p.exitcode < 0 \
+                            else f"Test exited with error {p.exitcode}"