Merge branch 'master' into sh_merge_master

.pre-commit-config.yaml

@@ -25,14 +25,14 @@ repos:
 
 # Clang format the codebase automatically
 - repo: https://github.com/pre-commit/mirrors-clang-format
-  rev: "v19.1.4"
+  rev: "v19.1.6"
   hooks:
   - id: clang-format
     types_or: [c++, c, cuda]
 
 # Ruff, the Python auto-correcting linter/formatter written in Rust
 - repo: https://github.com/astral-sh/ruff-pre-commit
-  rev: v0.8.1
+  rev: v0.8.6
   hooks:
   - id: ruff
     args: ["--fix", "--show-fixes"]
@@ -40,7 +40,7 @@ repos:
 
 # Check static types with mypy
 - repo: https://github.com/pre-commit/mirrors-mypy
-  rev: "v1.13.0"
+  rev: "v1.14.1"
   hooks:
   - id: mypy
     args: []
@@ -144,7 +144,7 @@ repos:
 
 # PyLint has native support - not always usable, but works for us
 - repo: https://github.com/PyCQA/pylint
-  rev: "v3.3.2"
+  rev: "v3.3.3"
   hooks:
   - id: pylint
     files: ^pybind11

docs/requirements.txt

@@ -130,9 +130,9 @@ imagesize==1.4.1 \
     --hash=sha256:0d8d18d08f840c19d0ee7ca1fd82490fdc3729b7ac93f49870406ddde8ef8d8b \
     --hash=sha256:69150444affb9cb0d5cc5a92b3676f0b2fb7cd9ae39e947a5e11a36b4497cd4a
     # via sphinx
-jinja2==3.1.4 \
-    --hash=sha256:4a3aee7acbbe7303aede8e9648d13b8bf88a429282aa6122a993f0ac800cb369 \
-    --hash=sha256:bc5dd2abb727a5319567b7a813e6a2e7318c39f4f487cfe6c89c6f9c7d25197d
+jinja2==3.1.5 \
+    --hash=sha256:8fefff8dc3034e27bb80d67c671eb8a9bc424c0ef4c0826edbff304cceff43bb \
+    --hash=sha256:aba0f4dc9ed8013c424088f68a5c226f7d6097ed89b246d7749c2ec4175c6adb
     # via sphinx
 markupsafe==2.1.5 \
     --hash=sha256:00e046b6dd71aa03a41079792f8473dc494d564611a8f89bbbd7cb93295ebdcf \

include/pybind11/detail/class.h

@@ -312,7 +312,31 @@ inline void traverse_offset_bases(void *valueptr,
     }
 }
 
+#ifdef Py_GIL_DISABLED
+inline void enable_try_inc_ref(PyObject *obj) {
+    // TODO: Replace with PyUnstable_Object_EnableTryIncRef when available.
+    // See https://github.com/python/cpython/issues/128844
+    if (_Py_IsImmortal(obj)) {
+        return;
+    }
+    for (;;) {
+        Py_ssize_t shared = _Py_atomic_load_ssize_relaxed(&obj->ob_ref_shared);
+        if ((shared & _Py_REF_SHARED_FLAG_MASK) != 0) {
+            // Nothing to do if it's in WEAKREFS, QUEUED, or MERGED states.
+            return;
+        }
+        if (_Py_atomic_compare_exchange_ssize(
+                &obj->ob_ref_shared, &shared, shared | _Py_REF_MAYBE_WEAKREF)) {
+            return;
+        }
+    }
+}
+#endif
+
 inline bool register_instance_impl(void *ptr, instance *self) {
+#ifdef Py_GIL_DISABLED
+    enable_try_inc_ref(reinterpret_cast<PyObject *>(self));
+#endif
     with_instance_map(ptr, [&](instance_map &instances) { instances.emplace(ptr, self); });
     return true; // unused, but gives the same signature as the deregister func
 }

include/pybind11/detail/type_caster_base.h

@@ -245,6 +245,49 @@ PYBIND11_NOINLINE handle get_type_handle(const std::type_info &tp, bool throw_if
     return handle(type_info ? ((PyObject *) type_info->type) : nullptr);
 }
 
+inline bool try_incref(PyObject *obj) {
+    // Tries to increment the reference count of an object if it's not zero.
+    // TODO: Use PyUnstable_TryIncref when available.
+    // See https://github.com/python/cpython/issues/128844
+#ifdef Py_GIL_DISABLED
+    // See
+    // https://github.com/python/cpython/blob/d05140f9f77d7dfc753dd1e5ac3a5962aaa03eff/Include/internal/pycore_object.h#L761
+    uint32_t local = _Py_atomic_load_uint32_relaxed(&obj->ob_ref_local);
+    local += 1;
+    if (local == 0) {
+        // immortal
+        return true;
+    }
+    if (_Py_IsOwnedByCurrentThread(obj)) {
+        _Py_atomic_store_uint32_relaxed(&obj->ob_ref_local, local);
+#    ifdef Py_REF_DEBUG
+        _Py_INCREF_IncRefTotal();
+#    endif
+        return true;
+    }
+    Py_ssize_t shared = _Py_atomic_load_ssize_relaxed(&obj->ob_ref_shared);
+    for (;;) {
+        // If the shared refcount is zero and the object is either merged
+        // or may not have weak references, then we cannot incref it.
+        if (shared == 0 || shared == _Py_REF_MERGED) {
+            return false;
+        }
+
+        if (_Py_atomic_compare_exchange_ssize(
+                &obj->ob_ref_shared, &shared, shared + (1 << _Py_REF_SHARED_SHIFT))) {
+#    ifdef Py_REF_DEBUG
+            _Py_INCREF_IncRefTotal();
+#    endif
+            return true;
+        }
+    }
+#else
+    assert(Py_REFCNT(obj) > 0);
+    Py_INCREF(obj);
+    return true;
+#endif
+}
+
 // Searches the inheritance graph for a registered Python instance, using all_type_info().
 PYBIND11_NOINLINE handle find_registered_python_instance(void *src,
                                                          const detail::type_info *tinfo) {
@@ -253,7 +296,10 @@ PYBIND11_NOINLINE handle find_registered_python_instance(void *src,
         for (auto it_i = it_instances.first; it_i != it_instances.second; ++it_i) {
             for (auto *instance_type : detail::all_type_info(Py_TYPE(it_i->second))) {
                 if (instance_type && same_type(*instance_type->cpptype, *tinfo->cpptype)) {
-                    return handle((PyObject *) it_i->second).inc_ref();
+                    auto *wrapper = reinterpret_cast<PyObject *>(it_i->second);
+                    if (try_incref(wrapper)) {
+                        return handle(wrapper);
+                    }
                 }
             }
         }

tests/test_thread.cpp

@@ -28,6 +28,9 @@ struct IntStruct {
     int value;
 };
 
+struct EmptyStruct {};
+EmptyStruct SharedInstance;
+
 } // namespace
 
 TEST_SUBMODULE(thread, m) {
@@ -61,6 +64,9 @@ TEST_SUBMODULE(thread, m) {
         },
         py::call_guard<py::gil_scoped_release>());
 
+    py::class_<EmptyStruct>(m, "EmptyStruct")
+        .def_readonly_static("SharedInstance", &SharedInstance);
+
     // NOTE: std::string_view also uses loader_life_support to ensure that
     // the string contents remain alive, but that's a C++ 17 feature.
 }

tests/test_thread.py

@@ -47,3 +47,22 @@ def test_implicit_conversion_no_gil():
         x.start()
     for x in [c, b, a]:
         x.join()
+
+
+@pytest.mark.skipif(sys.platform.startswith("emscripten"), reason="Requires threads")
+def test_bind_shared_instance():
+    nb_threads = 4
+    b = threading.Barrier(nb_threads)
+
+    def access_shared_instance():
+        b.wait()
+        for _ in range(1000):
+            m.EmptyStruct.SharedInstance  # noqa: B018
+
+    threads = [
+        threading.Thread(target=access_shared_instance) for _ in range(nb_threads)
+    ]
+    for thread in threads:
+        thread.start()
+    for thread in threads:
+        thread.join()