gh-113688: Split up gcmodule.c

This splits part of Modules/gcmodule.c of into Python/gc.c, which
now contains the core garbage collection implementation. The Python
module remain in the Modules/gcmodule.c file.

Author: colesbury

Include/internal/pycore_gc.h

@@ -64,6 +64,26 @@ static inline int _PyObject_GC_MAY_BE_TRACKED(PyObject *obj) {
 #define _PyGC_PREV_SHIFT           (2)
 #define _PyGC_PREV_MASK            (((uintptr_t) -1) << _PyGC_PREV_SHIFT)
 
+/* set for debugging information */
+#define _PyGC_DEBUG_STATS             (1<<0) /* print collection statistics */
+#define _PyGC_DEBUG_COLLECTABLE       (1<<1) /* print collectable objects */
+#define _PyGC_DEBUG_UNCOLLECTABLE     (1<<2) /* print uncollectable objects */
+#define _PyGC_DEBUG_SAVEALL           (1<<5) /* save all garbage in gc.garbage */
+#define _PyGC_DEBUG_LEAK              _PyGC_DEBUG_COLLECTABLE | \
+                                      _PyGC_DEBUG_UNCOLLECTABLE | \
+                                      _PyGC_DEBUG_SAVEALL
+
+typedef enum {
+    // GC was triggered by heap allocation
+    _Py_GC_REASON_HEAP,
+
+    // GC was called during shutdown
+    _Py_GC_REASON_SHUTDOWN,
+
+    // GC was called by gc.collect() or PyGC_Collect()
+    _Py_GC_REASON_MANUAL
+} _PyGC_Reason;
+
 // Lowest bit of _gc_next is used for flags only in GC.
 // But it is always 0 for normal code.
 static inline PyGC_Head* _PyGCHead_NEXT(PyGC_Head *gc) {
@@ -203,8 +223,19 @@ struct _gc_runtime_state {
 
 extern void _PyGC_InitState(struct _gc_runtime_state *);
 
+extern Py_ssize_t _PyGC_Collect(PyThreadState *tstate, int generation,
+                                _PyGC_Reason reason);
 extern Py_ssize_t _PyGC_CollectNoFail(PyThreadState *tstate);
 
+/* Freeze objects tracked by the GC and ignore them in future collections. */
+extern void _PyGC_Freeze(PyInterpreterState *interp);
+/* Unfreezes objects placing them in the oldest generation */
+extern void _PyGC_Unfreeze(PyInterpreterState *interp);
+/* Number of frozen objects */
+extern Py_ssize_t _PyGC_GetFreezeCount(PyInterpreterState *interp);
+
+extern PyObject *_PyGC_GetObjects(PyInterpreterState *interp, Py_ssize_t generation);
+extern PyObject *_PyGC_GetReferrers(PyInterpreterState *interp, PyObject *objs);
 
 // Functions to clear types free lists
 extern void _PyTuple_ClearFreeList(PyInterpreterState *interp);

Lib/test/test_gc.py

@@ -1225,7 +1225,7 @@ def test_refcount_errors(self):
         p.stderr.close()
         # Verify that stderr has a useful error message:
         self.assertRegex(stderr,
-            br'gcmodule\.c:[0-9]+: gc_decref: Assertion "gc_get_refs\(g\) > 0" failed.')
+            br'gc\.c:[0-9]+: gc_decref: Assertion "gc_get_refs\(g\) > 0" failed.')
         self.assertRegex(stderr,
             br'refcount is too small')
         # "address : 0x7fb5062efc18"

Makefile.pre.in

@@ -417,6 +417,7 @@ PYTHON_OBJS=	\
 		Python/frame.o \
 		Python/frozenmain.o \
 		Python/future.o \
+		Python/gc.o \
 		Python/getargs.o \
 		Python/getcompiler.o \
 		Python/getcopyright.o \