bpo-28254: Add a C-API for controlling the GC state (GH-25687)

Add new C-API functions to control the state of the garbage collector:
PyGC_Enable(), PyGC_Disable(), PyGC_IsEnabled(),
corresponding to the functions in the gc module.

Co-authored-by: Pablo Galindo <Pablogsal@gmail.com>
Co-authored-by: Victor Stinner <vstinner@python.org>

2 files changed, 91 insertions, 6 deletions

diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c
index db62aea..26ebacb 100644
--- a/Modules/_testcapimodule.c
+++ b/Modules/_testcapimodule.c
@@ -144,6 +144,67 @@ test_sizeof_c_types(PyObject *self, PyObject *Py_UNUSED(ignored))
 #endif
 }
 
+static PyObject*
+test_gc_control(PyObject *self, PyObject *Py_UNUSED(ignored))
+{
+    int orig_enabled = PyGC_IsEnabled();
+    const char* msg = "ok";
+    int old_state;
+
+    old_state = PyGC_Enable();
+    msg = "Enable(1)";
+    if (old_state != orig_enabled) {
+        goto failed;
+    }
+    msg = "IsEnabled(1)";
+    if (!PyGC_IsEnabled()) {
+        goto failed;
+    }
+
+    old_state = PyGC_Disable();
+    msg = "disable(2)";
+    if (!old_state) {
+        goto failed;
+    }
+    msg = "IsEnabled(2)";
+    if (PyGC_IsEnabled()) {
+        goto failed;
+    }
+
+    old_state = PyGC_Enable();
+    msg = "enable(3)";
+    if (old_state) {
+        goto failed;
+    }
+    msg = "IsEnabled(3)";
+    if (!PyGC_IsEnabled()) {
+        goto failed;
+    }
+
+    if (!orig_enabled) {
+        old_state = PyGC_Disable();
+        msg = "disable(4)";
+        if (old_state) {
+            goto failed;
+        }
+        msg = "IsEnabled(4)";
+        if (PyGC_IsEnabled()) {
+            goto failed;
+        }
+    }
+
+    Py_RETURN_NONE;
+
+failed:
+    /* Try to clean up if we can. */
+    if (orig_enabled) {
+        PyGC_Enable();
+    } else {
+        PyGC_Disable();
+    }
+    PyErr_Format(TestError, "GC control failed in %s", msg);
+    return NULL;
+}
 
 static PyObject*
 test_list_api(PyObject *self, PyObject *Py_UNUSED(ignored))
@@ -5544,6 +5605,7 @@ static PyMethodDef TestMethods[] = {
     {"PyDateTime_DATE_GET",        test_PyDateTime_DATE_GET,      METH_O},
     {"PyDateTime_TIME_GET",        test_PyDateTime_TIME_GET,      METH_O},
     {"PyDateTime_DELTA_GET",       test_PyDateTime_DELTA_GET,     METH_O},
+    {"test_gc_control",         test_gc_control,                 METH_NOARGS},
     {"test_list_api",           test_list_api,                   METH_NOARGS},
     {"test_dict_iteration",     test_dict_iteration,             METH_NOARGS},
     {"dict_getitem_knownhash",  dict_getitem_knownhash,          METH_VARARGS},
diff --git a/Modules/gcmodule.c b/Modules/gcmodule.c
index d6b5142..e5e5aa3 100644
--- a/Modules/gcmodule.c
+++ b/Modules/gcmodule.c
@@ -1484,8 +1484,7 @@ static PyObject *
 gc_enable_impl(PyObject *module)
 /*[clinic end generated code: output=45a427e9dce9155c input=81ac4940ca579707]*/
 {
-    GCState *gcstate = get_gc_state();
-    gcstate->enabled = 1;
+    PyGC_Enable();
     Py_RETURN_NONE;
 }
 
@@ -1499,8 +1498,7 @@ static PyObject *
 gc_disable_impl(PyObject *module)
 /*[clinic end generated code: output=97d1030f7aa9d279 input=8c2e5a14e800d83b]*/
 {
-    GCState *gcstate = get_gc_state();
-    gcstate->enabled = 0;
+    PyGC_Disable();
     Py_RETURN_NONE;
 }
 
@@ -1514,8 +1512,7 @@ static int
 gc_isenabled_impl(PyObject *module)
 /*[clinic end generated code: output=1874298331c49130 input=30005e0422373b31]*/
 {
-    GCState *gcstate = get_gc_state();
-    return gcstate->enabled;
+    return PyGC_IsEnabled();
 }
 
 /*[clinic input]
@@ -2053,6 +2050,32 @@ PyInit_gc(void)
     return PyModuleDef_Init(&gcmodule);
 }
 
+/* C API for controlling the state of the garbage collector */
+int
+PyGC_Enable(void)
+{
+    GCState *gcstate = get_gc_state();
+    int old_state = gcstate->enabled;
+    gcstate->enabled = 1;
+    return old_state;
+}
+
+int
+PyGC_Disable(void)
+{
+    GCState *gcstate = get_gc_state();
+    int old_state = gcstate->enabled;
+    gcstate->enabled = 0;
+    return old_state;
+}
+
+int
+PyGC_IsEnabled(void)
+{
+    GCState *gcstate = get_gc_state();
+    return gcstate->enabled;
+}
+
 /* Public API to invoke gc.collect() from C */
 Py_ssize_t
 PyGC_Collect(void)