/* Reference Cycle Garbage Collection ================================== Neil Schemenauer Based on a post on the python-dev list. Ideas from Guido van Rossum, Eric Tiedemann, and various others. http://www.arctrix.com/nas/python/gc/ The following mailing list threads provide a historical perspective on the design of this module. Note that a fair amount of refinement has occurred since those discussions. http://mail.python.org/pipermail/python-dev/2000-March/002385.html http://mail.python.org/pipermail/python-dev/2000-March/002434.html http://mail.python.org/pipermail/python-dev/2000-March/002497.html For a highlevel view of the collection process, read the collect function. */ #include "Python.h" #include "internal/mem.h" #include "internal/pystate.h" #include "frameobject.h" /* for PyFrame_ClearFreeList */ #include "pydtrace.h" #include "pytime.h" /* for _PyTime_GetMonotonicClock() */ /*[clinic input] module gc [clinic start generated code]*/ /*[clinic end generated code: output=da39a3ee5e6b4b0d input=b5c9690ecc842d79]*/ /* Get an object's GC head */ #define AS_GC(o) ((PyGC_Head *)(o)-1) /* Get the object given the GC head */ #define FROM_GC(g) ((PyObject *)(((PyGC_Head *)g)+1)) /* Python string to use if unhandled exception occurs */ static PyObject *gc_str = NULL; /* set for debugging information */ #define DEBUG_STATS (1<<0) /* print collection statistics */ #define DEBUG_COLLECTABLE (1<<1) /* print collectable objects */ #define DEBUG_UNCOLLECTABLE (1<<2) /* print uncollectable objects */ #define DEBUG_SAVEALL (1<<5) /* save all garbage in gc.garbage */ #define DEBUG_LEAK DEBUG_COLLECTABLE | \ DEBUG_UNCOLLECTABLE | \ DEBUG_SAVEALL #define GEN_HEAD(n) (&_PyRuntime.gc.generations[n].head) void _PyGC_Initialize(struct _gc_runtime_state *state) { state->enabled = 1; /* automatic collection enabled? */ #define _GEN_HEAD(n) (&state->generations[n].head) struct gc_generation generations[NUM_GENERATIONS] = { /* PyGC_Head, threshold, count */ {{{_GEN_HEAD(0), _GEN_HEAD(0), 0}}, 700, 0}, {{{_GEN_HEAD(1), _GEN_HEAD(1), 0}}, 10, 0}, {{{_GEN_HEAD(2), _GEN_HEAD(2), 0}}, 10, 0}, }; for (int i = 0; i < NUM_GENERATIONS; i++) { state->generations[i] = generations[i]; }; state->generation0 = GEN_HEAD(0); } /*-------------------------------------------------------------------------- gc_refs values. Between collections, every gc'ed object has one of two gc_refs values: GC_UNTRACKED The initial state; objects returned by PyObject_GC_Malloc are in this state. The object doesn't live in any generation list, and its tp_traverse slot must not be called. GC_REACHABLE The object lives in some generation list, and its tp_traverse is safe to call. An object transitions to GC_REACHABLE when PyObject_GC_Track is called. During a collection, gc_refs can temporarily take on other states: >= 0 At the start of a collection, update_refs() copies the true refcount to gc_refs, for each object in the generation being collected. subtract_refs() then adjusts gc_refs so that it equals the number of times an object is referenced directly from outside the generation being collected. gc_refs remains >= 0 throughout these steps. GC_TENTATIVELY_UNREACHABLE move_unreachable() then moves objects not reachable (whether directly or indirectly) from outside the generation into an "unreachable" set. Objects that are found to be reachable have gc_refs set to GC_REACHABLE again. Objects that are found to be unreachable have gc_refs set to GC_TENTATIVELY_UNREACHABLE. It's "tentatively" because the pass doing this can't be sure until it ends, and GC_TENTATIVELY_UNREACHABLE may transition back to GC_REACHABLE. Only objects with GC_TENTATIVELY_UNREACHABLE still set are candidates for collection. If it's decided not to collect such an object (e.g., it has a __del__ method), its gc_refs is restored to GC_REACHABLE again. ---------------------------------------------------------------------------- */ #define GC_UNTRACKED _PyGC_REFS_UNTRACKED #define GC_REACHABLE _PyGC_REFS_REACHABLE #define GC_TENTATIVELY_UNREACHABLE _PyGC_REFS_TENTATIVELY_UNREACHABLE #define IS_TRACKED(o) (_PyGC_REFS(o) != GC_UNTRACKED) #define IS_REACHABLE(o) (_PyGC_REFS(o) == GC_REACHABLE) #define IS_TENTATIVELY_UNREACHABLE(o) ( \ _PyGC_REFS(o) == GC_TENTATIVELY_UNREACHABLE) /*** list functions ***/ static void gc_list_init(PyGC_Head *list) { list->gc.gc_prev = list; list->gc.gc_next = list; } static int gc_list_is_empty(PyGC_Head *list) { return (list->gc.gc_next == list); } #if 0 /* This became unused after gc_list_move() was introduced. */ /* Append `node` to `list`. */ static void gc_list_append(PyGC_Head *node, PyGC_Head *list) { node->gc.gc_next = list; node->gc.gc_prev = list->gc.gc_prev; node->gc.gc_prev->gc.gc_next = node; list->gc.gc_prev = node; } #endif /* Remove `node` from the gc list it's currently in. */ static void gc_list_remove(PyGC_Head *node) { node->gc.gc_prev->gc.gc_next = node->gc.gc_next; node->gc.gc_next->gc.gc_prev = node->gc.gc_prev; node->gc.gc_next = NULL; /* object is not currently tracked */ } /* Move `node` from the gc list it's currently in (which is not explicitly * named here) to the end of `list`. This is semantically the same as * gc_list_remove(node) followed by gc_list_append(node, list). */ static void gc_list_move(PyGC_Head *node, PyGC_Head *list) { PyGC_Head *new_prev; PyGC_Head *current_prev = node->gc.gc_prev; PyGC_Head *current_next = node->gc.gc_next; /* Unlink from current list. */ current_prev->gc.gc_next = current_next; current_next->gc.gc_prev = current_prev; /* Relink at end of new list. */ new_prev = node->gc.gc_prev = list->gc.gc_prev; new_prev->gc.gc_next = list->gc.gc_prev = node; node->gc.gc_next = list; } /* append list `from` onto list `to`; `from` becomes an empty list */ static void gc_list_merge(PyGC_Head *from, PyGC_Head *to) { PyGC_Head *tail; assert(from != to); if (!gc_list_is_empty(from)) { tail = to->gc.gc_prev; tail->gc.gc_next = from->gc.gc_next; tail->gc.gc_next->gc.gc_prev = tail; to->gc.gc_prev = from->gc.gc_prev; to->gc.gc_prev->gc.gc_next = to; } gc_list_init(from); } static Py_ssize_t gc_list_size(PyGC_Head *list) { PyGC_Head *gc; Py_ssize_t n = 0; for (gc = list->gc.gc_next; gc != list; gc = gc->gc.gc_next) { n++; } return n; } /* Append objects in a GC list to a Python list. * Return 0 if all OK, < 0 if error (out of memory for list). */ static int append_objects(PyObject *py_list, PyGC_Head *gc_list) { PyGC_Head *gc; for (gc = gc_list->gc.gc_next; gc != gc_list; gc = gc->gc.gc_next) { PyObject *op = FROM_GC(gc); if (op != py_list) { if (PyList_Append(py_list, op)) { return -1; /* exception */ } } } return 0; } /*** end of list stuff ***/ /* Set all gc_refs = ob_refcnt. After this, gc_refs is > 0 for all objects * in containers, and is GC_REACHABLE for all tracked gc objects not in * containers. */ static void update_refs(PyGC_Head *containers) { PyGC_Head *gc = containers->gc.gc_next; for (; gc != containers; gc = gc->gc.gc_next) { assert(_PyGCHead_REFS(gc) == GC_REACHABLE); _PyGCHead_SET_REFS(gc, Py_REFCNT(FROM_GC(gc))); /* Python's cyclic gc should never see an incoming refcount * of 0: if something decref'ed to 0, it should have been * deallocated immediately at that time. * Possible cause (if the assert triggers): a tp_dealloc * routine left a gc-aware object tracked during its teardown * phase, and did something-- or allowed something to happen -- * that called back into Python. gc can trigger then, and may * see the still-tracked dying object. Before this assert * was added, such mistakes went on to allow gc to try to * delete the object again. In a debug build, that caused * a mysterious segfault, when _Py_ForgetReference tried * to remove the object from the doubly-linked list of all * objects a second time. In a release build, an actual * double deallocation occurred, which leads to corruption * of the allocator's internal bookkeeping pointers. That's * so serious that maybe this should be a release-build * check instead of an assert? */ assert(_PyGCHead_REFS(gc) != 0); } } /* A traversal callback for subtract_refs. */ static int visit_decref(PyObject *op, void *data) { assert(op != NULL); if (PyObject_IS_GC(op)) { PyGC_Head *gc = AS_GC(op); /* We're only interested in gc_refs for objects in the * generation being collected, which can be recognized * because only they have positive gc_refs. */ assert(_PyGCHead_REFS(gc) != 0); /* else refcount was too small */ if (_PyGCHead_REFS(gc) > 0) _PyGCHead_DECREF(gc); } return 0; } /* Subtract internal references from gc_refs. After this, gc_refs is >= 0 * for all objects in containers, and is GC_REACHABLE for all tracked gc * objects not in containers. The ones with gc_refs > 0 are directly * reachable from outside containers, and so can't be collected. */ static void subtract_refs(PyGC_Head *containers) { traverseproc traverse; PyGC_Head *gc = containers->gc.gc_next; for (; gc != containers; gc=gc->gc.gc_next) { traverse = Py_TYPE(FROM_GC(gc))->tp_traverse; (void) traverse(FROM_GC(gc), (visitproc)visit_decref, NULL); } } /* A traversal callback for move_unreachable. */ static int visit_reachable(PyObject *op, PyGC_Head *reachable) { if (PyObject_IS_GC(op)) { PyGC_Head *gc = AS_GC(op); const Py_ssize_t gc_refs = _PyGCHead_REFS(gc); if (gc_refs == 0) { /* This is in move_unreachable's 'young' list, but * the traversal hasn't yet gotten to it. All * we need to do is tell move_unreachable that it's * reachable. */ _PyGCHead_SET_REFS(gc, 1); } else if (gc_refs == GC_TENTATIVELY_UNREACHABLE) { /* This had gc_refs = 0 when move_unreachable got * to it, but turns out it's reachable after all. * Move it back to move_unreachable's 'young' list, * and move_unreachable will eventually get to it * again. */ gc_list_move(gc, reachable); _PyGCHead_SET_REFS(gc, 1); } /* Else there's nothing to do. * If gc_refs > 0, it must be in move_unreachable's 'young' * list, and move_unreachable will eventually get to it. * If gc_refs == GC_REACHABLE, it's either in some other * generation so we don't care about it, or move_unreachable * already dealt with it. * If gc_refs == GC_UNTRACKED, it must be ignored. */ else { assert(gc_refs > 0 || gc_refs == GC_REACHABLE || gc_refs == GC_UNTRACKED); } } return 0; } /* Move the unreachable objects from young to unreachable. After this, * all objects in young have gc_refs = GC_REACHABLE, and all objects in * unreachable have gc_refs = GC_TENTATIVELY_UNREACHABLE. All tracked * gc objects not in young or unreachable still have gc_refs = GC_REACHABLE. * All objects in young after this are directly or indirectly reachable * from outside the original young; and all objects in unreachable are * not. */ static void move_unreachable(PyGC_Head *young, PyGC_Head *unreachable) { PyGC_Head *gc = young->gc.gc_next; /* Invariants: all objects "to the left" of us in young have gc_refs * = GC_REACHABLE, and are indeed reachable (directly or indirectly) * from outside the young list as it was at entry. All other objects * from the original young "to the left" of us are in unreachable now, * and have gc_refs = GC_TENTATIVELY_UNREACHABLE. All objects to the * left of us in 'young' now have been scanned, and no objects here * or to the right have been scanned yet. */ while (gc != young) { PyGC_Head *next; if (_PyGCHead_REFS(gc)) { /* gc is definitely reachable from outside the * original 'young'. Mark it as such, and traverse * its pointers to find any other objects that may * be directly reachable from it. Note that the * call to tp_traverse may append objects to young, * so we have to wait until it returns to determine * the next object to visit. */ PyObject *op = FROM_GC(gc); traverseproc traverse = Py_TYPE(op)->tp_traverse; assert(_PyGCHead_REFS(gc) > 0); _PyGCHead_SET_REFS(gc, GC_REACHABLE); (void) traverse(op, (visitproc)visit_reachable, (void *)young); next = gc->gc.gc_next; if (PyTuple_CheckExact(op)) { _PyTuple_MaybeUntrack(op); } } else { /* This *may* be unreachable. To make progress, * assume it is. gc isn't directly reachable from * any object we've already traversed, but may be * reachable from an object we haven't gotten to yet. * visit_reachable will eventually move gc back into * young if that's so, and we'll see it again. */ next = gc->gc.gc_next; gc_list_move(gc, unreachable); _PyGCHead_SET_REFS(gc, GC_TENTATIVELY_UNREACHABLE); } gc = next; } } /* Try to untrack all currently tracked dictionaries */ static void untrack_dicts(PyGC_Head *head) { PyGC_Head *next, *gc = head->gc.gc_next; while (gc != head) { PyObject *op = FROM_GC(gc); next = gc->gc.gc_next; if (PyDict_CheckExact(op)) _PyDict_MaybeUntrack(op); gc = next; } } /* Return true if object has a pre-PEP 442 finalization method. */ static int has_legacy_finalizer(PyObject *op) { return op->ob_type->tp_del != NULL; } /* Move the objects in unreachable with tp_del slots into `finalizers`. * Objects moved into `finalizers` have gc_refs set to GC_REACHABLE; the * objects remaining in unreachable are left at GC_TENTATIVELY_UNREACHABLE. */ static void move_legacy_finalizers(PyGC_Head *unreachable, PyGC_Head *finalizers) { PyGC_Head *gc; PyGC_Head *next; /* March over unreachable. Move objects with finalizers into * `finalizers`. */ for (gc = unreachable->gc.gc_next; gc != unreachable; gc = next) { PyObject *op = FROM_GC(gc); assert(IS_TENTATIVELY_UNREACHABLE(op)); next = gc->gc.gc_next; if (has_legacy_finalizer(op)) { gc_list_move(gc, finalizers); _PyGCHead_SET_REFS(gc, GC_REACHABLE); } } } /* A traversal callback for move_legacy_finalizer_reachable. */ static int visit_move(PyObject *op, PyGC_Head *tolist) { if (PyObject_IS_GC(op)) { if (IS_TENTATIVELY_UNREACHABLE(op)) { PyGC_Head *gc = AS_GC(op); gc_list_move(gc, tolist); _PyGCHead_SET_REFS(gc, GC_REACHABLE); } } return 0; } /* Move objects that are reachable from finalizers, from the unreachable set * into finalizers set. */ static void move_legacy_finalizer_reachable(PyGC_Head *finalizers) { traverseproc traverse; PyGC_Head *gc = finalizers->gc.gc_next; for (; gc != finalizers; gc = gc->gc.gc_next) { /* Note that the finalizers list may grow during this. */ traverse = Py_TYPE(FROM_GC(gc))->tp_traverse; (void) traverse(FROM_GC(gc), (visitproc)visit_move, (void *)finalizers); } } /* Clear all weakrefs to unreachable objects, and if such a weakref has a * callback, invoke it if necessary. Note that it's possible for such * weakrefs to be outside the unreachable set -- indeed, those are precisely * the weakrefs whose callbacks must be invoked. See gc_weakref.txt for * overview & some details. Some weakrefs with callbacks may be reclaimed * directly by this routine; the number reclaimed is the return value. Other * weakrefs with callbacks may be moved into the `old` generation. Objects * moved into `old` have gc_refs set to GC_REACHABLE; the objects remaining in * unreachable are left at GC_TENTATIVELY_UNREACHABLE. When this returns, * no object in `unreachable` is weakly referenced anymore. */ static int handle_weakrefs(PyGC_Head *unreachable, PyGC_Head *old) { PyGC_Head *gc; PyObject *op; /* generally FROM_GC(gc) */ PyWeakReference *wr; /* generally a cast of op */ PyGC_Head wrcb_to_call; /* weakrefs with callbacks to call */ PyGC_Head *next; int num_freed = 0; gc_list_init(&wrcb_to_call); /* Clear all weakrefs to the objects in unreachable. If such a weakref * also has a callback, move it into `wrcb_to_call` if the callback * needs to be invoked. Note that we cannot invoke any callbacks until * all weakrefs to unreachable objects are cleared, lest the callback * resurrect an unreachable object via a still-active weakref. We * make another pass over wrcb_to_call, invoking callbacks, after this * pass completes. */ for (gc = unreachable->gc.gc_next; gc != unreachable; gc = next) { PyWeakReference **wrlist; op = FROM_GC(gc); assert(IS_TENTATIVELY_UNREACHABLE(op)); next = gc->gc.gc_next; if (! PyType_SUPPORTS_WEAKREFS(Py_TYPE(op))) continue; /* It supports weakrefs. Does it have any? */ wrlist = (PyWeakReference **) PyObject_GET_WEAKREFS_LISTPTR(op); /* `op` may have some weakrefs. March over the list, clear * all the weakrefs, and move the weakrefs with callbacks * that must be called into wrcb_to_call. */ for (wr = *wrlist; wr != NULL; wr = *wrlist) { PyGC_Head *wrasgc; /* AS_GC(wr) */ /* _PyWeakref_ClearRef clears the weakref but leaves * the callback pointer intact. Obscure: it also * changes *wrlist. */ assert(wr->wr_object == op); _PyWeakref_ClearRef(wr); assert(wr->wr_object == Py_None); if (wr->wr_callback == NULL) continue; /* no callback */ /* Headache time. `op` is going away, and is weakly referenced by * `wr`, which has a callback. Should the callback be invoked? If wr * is also trash, no: * * 1. There's no need to call it. The object and the weakref are * both going away, so it's legitimate to pretend the weakref is * going away first. The user has to ensure a weakref outlives its * referent if they want a guarantee that the wr callback will get * invoked. * * 2. It may be catastrophic to call it. If the callback is also in * cyclic trash (CT), then although the CT is unreachable from * outside the current generation, CT may be reachable from the * callback. Then the callback could resurrect insane objects. * * Since the callback is never needed and may be unsafe in this case, * wr is simply left in the unreachable set. Note that because we * already called _PyWeakref_ClearRef(wr), its callback will never * trigger. * * OTOH, if wr isn't part of CT, we should invoke the callback: the * weakref outlived the trash. Note that since wr isn't CT in this * case, its callback can't be CT either -- wr acted as an external * root to this generation, and therefore its callback did too. So * nothing in CT is reachable from the callback either, so it's hard * to imagine how calling it later could create a problem for us. wr * is moved to wrcb_to_call in this case. */ if (IS_TENTATIVELY_UNREACHABLE(wr)) continue; assert(IS_REACHABLE(wr)); /* Create a new reference so that wr can't go away * before we can process it again. */ Py_INCREF(wr); /* Move wr to wrcb_to_call, for the next pass. */ wrasgc = AS_GC(wr); assert(wrasgc != next); /* wrasgc is reachable, but next isn't, so they can't be the same */ gc_list_move(wrasgc, &wrcb_to_call); } } /* Invoke the callbacks we decided to honor. It's safe to invoke them * because they can't reference unreachable objects. */ while (! gc_list_is_empty(&wrcb_to_call)) { PyObject *temp; PyObject *callback; gc = wrcb_to_call.gc.gc_next; op = FROM_GC(gc); assert(IS_REACHABLE(op)); assert(PyWeakref_Check(op)); wr = (PyWeakReference *)op; callback = wr->wr_callback; assert(callback != NULL); /* copy-paste of weakrefobject.c's handle_callback() */ temp = PyObject_CallFunctionObjArgs(callback, wr, NULL); if (temp == NULL) PyErr_WriteUnraisable(callback); else Py_DECREF(temp); /* Give up the reference we created in the first pass. When * op's refcount hits 0 (which it may or may not do right now), * op's tp_dealloc will decref op->wr_callback too. Note * that the refcount probably will hit 0 now, and because this * weakref was reachable to begin with, gc didn't already * add it to its count of freed objects. Example: a reachable * weak value dict maps some key to this reachable weakref. * The callback removes this key->weakref mapping from the * dict, leaving no other references to the weakref (excepting * ours). */ Py_DECREF(op); if (wrcb_to_call.gc.gc_next == gc) { /* object is still alive -- move it */ gc_list_move(gc, old); } else ++num_freed; } return num_freed; } static void debug_cycle(const char *msg, PyObject *op) { PySys_FormatStderr("gc: %s <%s %p>\n", msg, Py_TYPE(op)->tp_name, op); } /* Handle uncollectable garbage (cycles with tp_del slots, and stuff reachable * only from such cycles). * If DEBUG_SAVEALL, all objects in finalizers are appended to the module * garbage list (a Python list), else only the objects in finalizers with * __del__ methods are appended to garbage. All objects in finalizers are * merged into the old list regardless. * Returns 0 if all OK, <0 on error (out of memory to grow the garbage list). * The finalizers list is made empty on a successful return. */ static int handle_legacy_finalizers(PyGC_Head *finalizers, PyGC_Head *old) { PyGC_Head *gc = finalizers->gc.gc_next; if (_PyRuntime.gc.garbage == NULL) { _PyRuntime.gc.garbage = PyList_New(0); if (_PyRuntime.gc.garbage == NULL) Py_FatalError("gc couldn't create gc.garbage list"); } for (; gc != finalizers; gc = gc->gc.gc_next) { PyObject *op = FROM_GC(gc); if ((_PyRuntime.gc.debug & DEBUG_SAVEALL) || has_legacy_finalizer(op)) { if (PyList_Append(_PyRuntime.gc.garbage, op) < 0) return -1; } } gc_list_merge(finalizers, old); return 0; } /* Run first-time finalizers (if any) on all the objects in collectable. * Note that this may remove some (or even all) of the objects from the * list, due to refcounts falling to 0. */ static void finalize_garbage(PyGC_Head *collectable) { destructor finalize; PyGC_Head seen; /* While we're going through the loop, `finalize(op)` may cause op, or * other objects, to be reclaimed via refcounts falling to zero. So * there's little we can rely on about the structure of the input * `collectable` list across iterations. For safety, we always take the * first object in that list and move it to a temporary `seen` list. * If objects vanish from the `collectable` and `seen` lists we don't * care. */ gc_list_init(&seen); while (!gc_list_is_empty(collectable)) { PyGC_Head *gc = collectable->gc.gc_next; PyObject *op = FROM_GC(gc); gc_list_move(gc, &seen); if (!_PyGCHead_FINALIZED(gc) && PyType_HasFeature(Py_TYPE(op), Py_TPFLAGS_HAVE_FINALIZE) && (finalize = Py_TYPE(op)->tp_finalize) != NULL) { _PyGCHead_SET_FINALIZED(gc, 1); Py_INCREF(op); finalize(op); Py_DECREF(op); } } gc_list_merge(&seen, collectable); } /* Walk the collectable list and check that they are really unreachable from the outside (some objects could have been resurrected by a finalizer). */ static int check_garbage(PyGC_Head *collectable) { PyGC_Head *gc; for (gc = collectable->gc.gc_next; gc != collectable; gc = gc->gc.gc_next) { _PyGCHead_SET_REFS(gc, Py_REFCNT(FROM_GC(gc))); assert(_PyGCHead_REFS(gc) != 0); } subtract_refs(collectable); for (gc = collectable->gc.gc_next; gc != collectable; gc = gc->gc.gc_next) { assert(_PyGCHead_REFS(gc) >= 0); if (_PyGCHead_REFS(gc) != 0) return -1; } return 0; } static void revive_garbage(PyGC_Head *collectable) { PyGC_Head *gc; for (gc = collectable->gc.gc_next; gc != collectable; gc = gc->gc.gc_next) { _PyGCHead_SET_REFS(gc, GC_REACHABLE); } } /* Break reference cycles by clearing the containers involved. This is * tricky business as the lists can be changing and we don't know which * objects may be freed. It is possible I screwed something up here. */ static void delete_garbage(PyGC_Head *collectable, PyGC_Head *old) { inquiry clear; while (!gc_list_is_empty(collectable)) { PyGC_Head *gc = collectable->gc.gc_next; PyObject *op = FROM_GC(gc); if (_PyRuntime.gc.debug & DEBUG_SAVEALL) { PyList_Append(_PyRuntime.gc.garbage, op); } else { if ((clear = Py_TYPE(op)->tp_clear) != NULL) { Py_INCREF(op); clear(op); Py_DECREF(op); } } if (collectable->gc.gc_next == gc) { /* object is still alive, move it, it may die later */ gc_list_move(gc, old); _PyGCHead_SET_REFS(gc, GC_REACHABLE); } } } /* Clear all free lists * All free lists are cleared during the collection of the highest generation. * Allocated items in the free list may keep a pymalloc arena occupied. * Clearing the free lists may give back memory to the OS earlier. */ static void clear_freelists(void) { (void)PyMethod_ClearFreeList(); (void)PyFrame_ClearFreeList(); (void)PyCFunction_ClearFreeList(); (void)PyTuple_ClearFreeList(); (void)PyUnicode_ClearFreeList(); (void)PyFloat_ClearFreeList(); (void)PyList_ClearFreeList(); (void)PyDict_ClearFreeList(); (void)PySet_ClearFreeList(); (void)PyAsyncGen_ClearFreeLists(); } /* This is the main function. Read this to understand how the * collection process works. */ static Py_ssize_t collect(int generation, Py_ssize_t *n_collected, Py_ssize_t *n_uncollectable, int nofail) { int i; Py_ssize_t m = 0; /* # objects collected */ Py_ssize_t n = 0; /* # unreachable objects that couldn't be collected */ PyGC_Head *young; /* the generation we are examining */ PyGC_Head *old; /* next older generation */ PyGC_Head unreachable; /* non-problematic unreachable trash */ PyGC_Head finalizers; /* objects with, & reachable from, __del__ */ PyGC_Head *gc; _PyTime_t t1 = 0; /* initialize to prevent a compiler warning */ struct gc_generation_stats *stats = &_PyRuntime.gc.generation_stats[generation]; if (_PyRuntime.gc.debug & DEBUG_STATS) { PySys_WriteStderr("gc: collecting generation %d...\n", generation); PySys_WriteStderr("gc: objects in each generation:"); for (i = 0; i < NUM_GENERATIONS; i++) PySys_FormatStderr(" %zd", gc_list_size(GEN_HEAD(i))); t1 = _PyTime_GetMonotonicClock(); PySys_WriteStderr("\n"); } if (PyDTrace_GC_START_ENABLED()) PyDTrace_GC_START(generation); /* update collection and allocation counters */ if (generation+1 < NUM_GENERATIONS) _PyRuntime.gc.generations[generation+1].count += 1; for (i = 0; i <= generation; i++) _PyRuntime.gc.generations[i].count = 0; /* merge younger generations with one we are currently collecting */ for (i = 0; i < generation; i++) { gc_list_merge(GEN_HEAD(i), GEN_HEAD(generation)); } /* handy references */ young = GEN_HEAD(generation); if (generation < NUM_GENERATIONS-1) old = GEN_HEAD(generation+1); else old = young; /* Using ob_refcnt and gc_refs, calculate which objects in the * container set are reachable from outside the set (i.e., have a * refcount greater than 0 when all the references within the * set are taken into account). */ update_refs(young); subtract_refs(young); /* Leave everything reachable from outside young in young, and move * everything else (in young) to unreachable. * NOTE: This used to move the reachable objects into a reachable * set instead. But most things usually turn out to be reachable, * so it's more efficient to move the unreachable things. */ gc_list_init(&unreachable); move_unreachable(young, &unreachable); /* Move reachable objects to next generation. */ if (young != old) { if (generation == NUM_GENERATIONS - 2) { _PyRuntime.gc.long_lived_pending += gc_list_size(young); } gc_list_merge(young, old); } else { /* We only untrack dicts in full collections, to avoid quadratic dict build-up. See issue #14775. */ untrack_dicts(young); _PyRuntime.gc.long_lived_pending = 0; _PyRuntime.gc.long_lived_total = gc_list_size(young); } /* All objects in unreachable are trash, but objects reachable from * legacy finalizers (e.g. tp_del) can't safely be deleted. */ gc_list_init(&finalizers); move_legacy_finalizers(&unreachable, &finalizers); /* finalizers contains the unreachable objects with a legacy finalizer; * unreachable objects reachable *from* those are also uncollectable, * and we move those into the finalizers list too. */ move_legacy_finalizer_reachable(&finalizers); /* Collect statistics on collectable objects found and print * debugging information. */ for (gc = unreachable.gc.gc_next; gc != &unreachable; gc = gc->gc.gc_next) { m++; if (_PyRuntime.gc.debug & DEBUG_COLLECTABLE) { debug_cycle("collectable", FROM_GC(gc)); } } /* Clear weakrefs and invoke callbacks as necessary. */ m += handle_weakrefs(&unreachable, old); /* Call tp_finalize on objects which have one. */ finalize_garbage(&unreachable); if (check_garbage(&unreachable)) { revive_garbage(&unreachable); gc_list_merge(&unreachable, old); } else { /* Call tp_clear on objects in the unreachable set. This will cause * the reference cycles to be broken. It may also cause some objects * in finalizers to be freed. */ delete_garbage(&unreachable, old); } /* Collect statistics on uncollectable objects found and print * debugging information. */ for (gc = finalizers.gc.gc_next; gc != &finalizers; gc = gc->gc.gc_next) { n++; if (_PyRuntime.gc.debug & DEBUG_UNCOLLECTABLE) debug_cycle("uncollectable", FROM_GC(gc)); } if (_PyRuntime.gc.debug & DEBUG_STATS) { _PyTime_t t2 = _PyTime_GetMonotonicClock(); if (m == 0 && n == 0) PySys_WriteStderr("gc: done"); else PySys_FormatStderr( "gc: done, %zd unreachable, %zd uncollectable", n+m, n); PySys_WriteStderr(", %.4fs elapsed\n", _PyTime_AsSecondsDouble(t2 - t1)); } /* Append instances in the uncollectable set to a Python * reachable list of garbage. The programmer has to deal with * this if they insist on creating this type of structure. */ (void)handle_legacy_finalizers(&finalizers, old); /* Clear free list only during the collection of the highest * generation */ if (generation == NUM_GENERATIONS-1) { clear_freelists(); } if (PyErr_Occurred()) { if (nofail) { PyErr_Clear(); } else { if (gc_str == NULL) gc_str = PyUnicode_FromString("garbage collection"); PyErr_WriteUnraisable(gc_str); Py_FatalError("unexpected exception during garbage collection"); } } /* Update stats */ if (n_collected) *n_collected = m; if (n_uncollectable) *n_uncollectable = n; stats->collections++; stats->collected += m; stats->uncollectable += n; if (PyDTrace_GC_DONE_ENABLED()) PyDTrace_GC_DONE(n+m); return n+m; } /* Invoke progress callbacks to notify clients that garbage collection * is starting or stopping */ static void invoke_gc_callback(const char *phase, int generation, Py_ssize_t collected, Py_ssize_t uncollectable) { Py_ssize_t i; PyObject *info = NULL; /* we may get called very early */ if (_PyRuntime.gc.callbacks == NULL) return; /* The local variable cannot be rebound, check it for sanity */ assert(_PyRuntime.gc.callbacks != NULL && PyList_CheckExact(_PyRuntime.gc.callbacks)); if (PyList_GET_SIZE(_PyRuntime.gc.callbacks) != 0) { info = Py_BuildValue("{sisnsn}", "generation", generation, "collected", collected, "uncollectable", uncollectable); if (info == NULL) { PyErr_WriteUnraisable(NULL); return; } } for (i=0; i= 0; i--) { if (_PyRuntime.gc.generations[i].count > _PyRuntime.gc.generations[i].threshold) { /* Avoid quadratic performance degradation in number of tracked objects. See comments at the beginning of this file, and issue #4074. */ if (i == NUM_GENERATIONS - 1 && _PyRuntime.gc.long_lived_pending < _PyRuntime.gc.long_lived_total / 4) continue; n = collect_with_callback(i); break; } } return n; } #include "clinic/gcmodule.c.h" /*[clinic input] gc.enable Enable automatic garbage collection. [clinic start generated code]*/ static PyObject * gc_enable_impl(PyObject *module) /*[clinic end generated code: output=45a427e9dce9155c input=81ac4940ca579707]*/ { _PyRuntime.gc.enabled = 1; Py_RETURN_NONE; } /*[clinic input] gc.disable Disable automatic garbage collection. [clinic start generated code]*/ static PyObject * gc_disable_impl(PyObject *module) /*[clinic end generated code: output=97d1030f7aa9d279 input=8c2e5a14e800d83b]*/ { _PyRuntime.gc.enabled = 0; Py_RETURN_NONE; } /*[clinic input] gc.isenabled -> bool Returns true if automatic garbage collection is enabled. [clinic start generated code]*/ static int gc_isenabled_impl(PyObject *module) /*[clinic end generated code: output=1874298331c49130 input=30005e0422373b31]*/ { return _PyRuntime.gc.enabled; } /*[clinic input] gc.collect -> Py_ssize_t generation: int(c_default="NUM_GENERATIONS - 1") = 2 Run the garbage collector. With no arguments, run a full collection. The optional argument may be an integer specifying which generation to collect. A ValueError is raised if the generation number is invalid. The number of unreachable objects is returned. [clinic start generated code]*/ static Py_ssize_t gc_collect_impl(PyObject *module, int generation) /*[clinic end generated code: output=b697e633043233c7 input=40720128b682d879]*/ { Py_ssize_t n; if (generation < 0 || generation >= NUM_GENERATIONS) { PyErr_SetString(PyExc_ValueError, "invalid generation"); return -1; } if (_PyRuntime.gc.collecting) n = 0; /* already collecting, don't do anything */ else { _PyRuntime.gc.collecting = 1; n = collect_with_callback(generation); _PyRuntime.gc.collecting = 0; } return n; } /*[clinic input] gc.set_debug flags: int An integer that can have the following bits turned on: DEBUG_STATS - Print statistics during collection. DEBUG_COLLECTABLE - Print collectable objects found. DEBUG_UNCOLLECTABLE - Print unreachable but uncollectable objects found. DEBUG_SAVEALL - Save objects to gc.garbage rather than freeing them. DEBUG_LEAK - Debug leaking programs (everything but STATS). / Set the garbage collection debugging flags. Debugging information is written to sys.stderr. [clinic start generated code]*/ static PyObject * gc_set_debug_impl(PyObject *module, int flags) /*[clinic end generated code: output=7c8366575486b228 input=5e5ce15e84fbed15]*/ { _PyRuntime.gc.debug = flags; Py_RETURN_NONE; } /*[clinic input] gc.get_debug -> int Get the garbage collection debugging flags. [clinic start generated code]*/ static int gc_get_debug_impl(PyObject *module) /*[clinic end generated code: output=91242f3506cd1e50 input=91a101e1c3b98366]*/ { return _PyRuntime.gc.debug; } PyDoc_STRVAR(gc_set_thresh__doc__, "set_threshold(threshold0, [threshold1, threshold2]) -> None\n" "\n" "Sets the collection thresholds. Setting threshold0 to zero disables\n" "collection.\n"); static PyObject * gc_set_thresh(PyObject *self, PyObject *args) { int i; if (!PyArg_ParseTuple(args, "i|ii:set_threshold", &_PyRuntime.gc.generations[0].threshold, &_PyRuntime.gc.generations[1].threshold, &_PyRuntime.gc.generations[2].threshold)) return NULL; for (i = 2; i < NUM_GENERATIONS; i++) { /* generations higher than 2 get the same threshold */ _PyRuntime.gc.generations[i].threshold = _PyRuntime.gc.generations[2].threshold; } Py_RETURN_NONE; } /*[clinic input] gc.get_threshold Return the current collection thresholds. [clinic start generated code]*/ static PyObject * gc_get_threshold_impl(PyObject *module) /*[clinic end generated code: output=7902bc9f41ecbbd8 input=286d79918034d6e6]*/ { return Py_BuildValue("(iii)", _PyRuntime.gc.generations[0].threshold, _PyRuntime.gc.generations[1].threshold, _PyRuntime.gc.generations[2].threshold); } /*[clinic input] gc.get_count Return a three-tuple of the current collection counts. [clinic start generated code]*/ static PyObject * gc_get_count_impl(PyObject *module) /*[clinic end generated code: output=354012e67b16398f input=a392794a08251751]*/ { return Py_BuildValue("(iii)", _PyRuntime.gc.generations[0].count, _PyRuntime.gc.generations[1].count, _PyRuntime.gc.generations[2].count); } static int referrersvisit(PyObject* obj, PyObject *objs) { Py_ssize_t i; for (i = 0; i < PyTuple_GET_SIZE(objs); i++) if (PyTuple_GET_ITEM(objs, i) == obj) return 1; return 0; } static int gc_referrers_for(PyObject *objs, PyGC_Head *list, PyObject *resultlist) { PyGC_Head *gc; PyObject *obj; traverseproc traverse; for (gc = list->gc.gc_next; gc != list; gc = gc->gc.gc_next) { obj = FROM_GC(gc); traverse = Py_TYPE(obj)->tp_traverse; if (obj == objs || obj == resultlist) continue; if (traverse(obj, (visitproc)referrersvisit, objs)) { if (PyList_Append(resultlist, obj) < 0) return 0; /* error */ } } return 1; /* no error */ } PyDoc_STRVAR(gc_get_referrers__doc__, "get_referrers(*objs) -> list\n\ Return the list of objects that directly refer to any of objs."); static PyObject * gc_get_referrers(PyObject *self, PyObject *args) { int i; PyObject *result = PyList_New(0); if (!result) return NULL; for (i = 0; i < NUM_GENERATIONS; i++) { if (!(gc_referrers_for(args, GEN_HEAD(i), result))) { Py_DECREF(result); return NULL; } } return result; } /* Append obj to list; return true if error (out of memory), false if OK. */ static int referentsvisit(PyObject *obj, PyObject *list) { return PyList_Append(list, obj) < 0; } PyDoc_STRVAR(gc_get_referents__doc__, "get_referents(*objs) -> list\n\ Return the list of objects that are directly referred to by objs."); static PyObject * gc_get_referents(PyObject *self, PyObject *args) { Py_ssize_t i; PyObject *result = PyList_New(0); if (result == NULL) return NULL; for (i = 0; i < PyTuple_GET_SIZE(args); i++) { traverseproc traverse; PyObject *obj = PyTuple_GET_ITEM(args, i); if (! PyObject_IS_GC(obj)) continue; traverse = Py_TYPE(obj)->tp_traverse; if (! traverse) continue; if (traverse(obj, (visitproc)referentsvisit, result)) { Py_DECREF(result); return NULL; } } return result; } /*[clinic input] gc.get_objects Return a list of objects tracked by the collector (excluding the list returned). [clinic start generated code]*/ static PyObject * gc_get_objects_impl(PyObject *module) /*[clinic end generated code: output=fcb95d2e23e1f750 input=9439fe8170bf35d8]*/ { int i; PyObject* result; result = PyList_New(0); if (result == NULL) return NULL; for (i = 0; i < NUM_GENERATIONS; i++) { if (append_objects(result, GEN_HEAD(i))) { Py_DECREF(result); return NULL; } } return result; } /*[clinic input] gc.get_stats Return a list of dictionaries containing per-generation statistics. [clinic start generated code]*/ static PyObject * gc_get_stats_impl(PyObject *module) /*[clinic end generated code: output=a8ab1d8a5d26f3ab input=1ef4ed9d17b1a470]*/ { int i; PyObject *result; struct gc_generation_stats stats[NUM_GENERATIONS], *st; /* To get consistent values despite allocations while constructing the result list, we use a snapshot of the running stats. */ for (i = 0; i < NUM_GENERATIONS; i++) { stats[i] = _PyRuntime.gc.generation_stats[i]; } result = PyList_New(0); if (result == NULL) return NULL; for (i = 0; i < NUM_GENERATIONS; i++) { PyObject *dict; st = &stats[i]; dict = Py_BuildValue("{snsnsn}", "collections", st->collections, "collected", st->collected, "uncollectable", st->uncollectable ); if (dict == NULL) goto error; if (PyList_Append(result, dict)) { Py_DECREF(dict); goto error; } Py_DECREF(dict); } return result; error: Py_XDECREF(result); return NULL; } /*[clinic input] gc.is_tracked obj: object / Returns true if the object is tracked by the garbage collector. Simple atomic objects will return false. [clinic start generated code]*/ static PyObject * gc_is_tracked(PyObject *module, PyObject *obj) /*[clinic end generated code: output=14f0103423b28e31 input=d83057f170ea2723]*/ { PyObject *result; if (PyObject_IS_GC(obj) && IS_TRACKED(obj)) result = Py_True; else result = Py_False; Py_INCREF(result); return result; } PyDoc_STRVAR(gc__doc__, "This module provides access to the garbage collector for reference cycles.\n" "\n" "enable() -- Enable automatic garbage collection.\n" "disable() -- Disable automatic garbage collection.\n" "isenabled() -- Returns true if automatic collection is enabled.\n" "collect() -- Do a full collection right now.\n" "get_count() -- Return the current collection counts.\n" "get_stats() -- Return list of dictionaries containing per-generation stats.\n" "set_debug() -- Set debugging flags.\n" "get_debug() -- Get debugging flags.\n" "set_threshold() -- Set the collection thresholds.\n" "get_threshold() -- Return the current the collection thresholds.\n" "get_objects() -- Return a list of all objects tracked by the collector.\n" "is_tracked() -- Returns true if a given object is tracked.\n" "get_referrers() -- Return the list of objects that refer to an object.\n" "get_referents() -- Return the list of objects that an object refers to.\n"); static PyMethodDef GcMethods[] = { GC_ENABLE_METHODDEF GC_DISABLE_METHODDEF GC_ISENABLED_METHODDEF GC_SET_DEBUG_METHODDEF GC_GET_DEBUG_METHODDEF GC_GET_COUNT_METHODDEF {"set_threshold", gc_set_thresh, METH_VARARGS, gc_set_thresh__doc__}, GC_GET_THRESHOLD_METHODDEF GC_COLLECT_METHODDEF GC_GET_OBJECTS_METHODDEF GC_GET_STATS_METHODDEF GC_IS_TRACKED_METHODDEF {"get_referrers", gc_get_referrers, METH_VARARGS, gc_get_referrers__doc__}, {"get_referents", gc_get_referents, METH_VARARGS, gc_get_referents__doc__}, {NULL, NULL} /* Sentinel */ }; static struct PyModuleDef gcmodule = { PyModuleDef_HEAD_INIT, "gc", /* m_name */ gc__doc__, /* m_doc */ -1, /* m_size */ GcMethods, /* m_methods */ NULL, /* m_reload */ NULL, /* m_traverse */ NULL, /* m_clear */ NULL /* m_free */ }; PyMODINIT_FUNC PyInit_gc(void) { PyObject *m; m = PyModule_Create(&gcmodule); if (m == NULL) return NULL; if (_PyRuntime.gc.garbage == NULL) { _PyRuntime.gc.garbage = PyList_New(0); if (_PyRuntime.gc.garbage == NULL) return NULL; } Py_INCREF(_PyRuntime.gc.garbage); if (PyModule_AddObject(m, "garbage", _PyRuntime.gc.garbage) < 0) return NULL; if (_PyRuntime.gc.callbacks == NULL) { _PyRuntime.gc.callbacks = PyList_New(0); if (_PyRuntime.gc.callbacks == NULL) return NULL; } Py_INCREF(_PyRuntime.gc.callbacks); if (PyModule_AddObject(m, "callbacks", _PyRuntime.gc.callbacks) < 0) return NULL; #define ADD_INT(NAME) if (PyModule_AddIntConstant(m, #NAME, NAME) < 0) return NULL ADD_INT(DEBUG_STATS); ADD_INT(DEBUG_COLLECTABLE); ADD_INT(DEBUG_UNCOLLECTABLE); ADD_INT(DEBUG_SAVEALL); ADD_INT(DEBUG_LEAK); #undef ADD_INT return m; } /* API to invoke gc.collect() from C */ Py_ssize_t PyGC_Collect(void) { Py_ssize_t n; if (_PyRuntime.gc.collecting) n = 0; /* already collecting, don't do anything */ else { _PyRuntime.gc.collecting = 1; n = collect_with_callback(NUM_GENERATIONS - 1); _PyRuntime.gc.collecting = 0; } return n; } Py_ssize_t _PyGC_CollectIfEnabled(void) { if (!_PyRuntime.gc.enabled) return 0; return PyGC_Collect(); } Py_ssize_t _PyGC_CollectNoFail(void) { Py_ssize_t n; /* Ideally, this function is only called on interpreter shutdown, and therefore not recursively. Unfortunately, when there are daemon threads, a daemon thread can start a cyclic garbage collection during interpreter shutdown (and then never finish it). See http://bugs.python.org/issue8713#msg195178 for an example. */ if (_PyRuntime.gc.collecting) n = 0; else { _PyRuntime.gc.collecting = 1; n = collect(NUM_GENERATIONS - 1, NULL, NULL, 1); _PyRuntime.gc.collecting = 0; } return n; } void _PyGC_DumpShutdownStats(void) { if (!(_PyRuntime.gc.debug & DEBUG_SAVEALL) && _PyRuntime.gc.garbage != NULL && PyList_GET_SIZE(_PyRuntime.gc.garbage) > 0) { char *message; if (_PyRuntime.gc.debug & DEBUG_UNCOLLECTABLE) message = "gc: %zd uncollectable objects at " \ "shutdown"; else message = "gc: %zd uncollectable objects at " \ "shutdown; use gc.set_debug(gc.DEBUG_UNCOLLECTABLE) to list them"; /* PyErr_WarnFormat does too many things and we are at shutdown, the warnings module's dependencies (e.g. linecache) may be gone already. */ if (PyErr_WarnExplicitFormat(PyExc_ResourceWarning, "gc", 0, "gc", NULL, message, PyList_GET_SIZE(_PyRuntime.gc.garbage))) PyErr_WriteUnraisable(NULL); if (_PyRuntime.gc.debug & DEBUG_UNCOLLECTABLE) { PyObject *repr = NULL, *bytes = NULL; repr = PyObject_Repr(_PyRuntime.gc.garbage); if (!repr || !(bytes = PyUnicode_EncodeFSDefault(repr))) PyErr_WriteUnraisable(_PyRuntime.gc.garbage); else { PySys_WriteStderr( " %s\n", PyBytes_AS_STRING(bytes) ); } Py_XDECREF(repr); Py_XDECREF(bytes); } } } void _PyGC_Fini(void) { Py_CLEAR(_PyRuntime.gc.callbacks); } /* for debugging */ void _PyGC_Dump(PyGC_Head *g) { _PyObject_Dump(FROM_GC(g)); } /* extension modules might be compiled with GC support so these functions must always be available */ #undef PyObject_GC_Track #undef PyObject_GC_UnTrack #undef PyObject_GC_Del #undef _PyObject_GC_Malloc void PyObject_GC_Track(void *op) { _PyObject_GC_TRACK(op); } void PyObject_GC_UnTrack(void *op) { /* Obscure: the Py_TRASHCAN mechanism requires that we be able to * call PyObject_GC_UnTrack twice on an object. */ if (IS_TRACKED(op)) _PyObject_GC_UNTRACK(op); } static PyObject * _PyObject_GC_Alloc(int use_calloc, size_t basicsize) { PyObject *op; PyGC_Head *g; size_t size; if (basicsize > PY_SSIZE_T_MAX - sizeof(PyGC_Head)) return PyErr_NoMemory(); size = sizeof(PyGC_Head) + basicsize; if (use_calloc) g = (PyGC_Head *)PyObject_Calloc(1, size); else g = (PyGC_Head *)PyObject_Malloc(size); if (g == NULL) return PyErr_NoMemory(); g->gc.gc_refs = 0; _PyGCHead_SET_REFS(g, GC_UNTRACKED); _PyRuntime.gc.generations[0].count++; /* number of allocated GC objects */ if (_PyRuntime.gc.generations[0].count > _PyRuntime.gc.generations[0].threshold && _PyRuntime.gc.enabled && _PyRuntime.gc.generations[0].threshold && !_PyRuntime.gc.collecting && !PyErr_Occurred()) { _PyRuntime.gc.collecting = 1; collect_generations(); _PyRuntime.gc.collecting = 0; } op = FROM_GC(g); return op; } PyObject * _PyObject_GC_Malloc(size_t basicsize) { return _PyObject_GC_Alloc(0, basicsize); } PyObject * _PyObject_GC_Calloc(size_t basicsize) { return _PyObject_GC_Alloc(1, basicsize); } PyObject * _PyObject_GC_New(PyTypeObject *tp) { PyObject *op = _PyObject_GC_Malloc(_PyObject_SIZE(tp)); if (op != NULL) op = PyObject_INIT(op, tp); return op; } PyVarObject * _PyObject_GC_NewVar(PyTypeObject *tp, Py_ssize_t nitems) { size_t size; PyVarObject *op; if (nitems < 0) { PyErr_BadInternalCall(); return NULL; } size = _PyObject_VAR_SIZE(tp, nitems); op = (PyVarObject *) _PyObject_GC_Malloc(size); if (op != NULL) op = PyObject_INIT_VAR(op, tp, nitems); return op; } PyVarObject * _PyObject_GC_Resize(PyVarObject *op, Py_ssize_t nitems) { const size_t basicsize = _PyObject_VAR_SIZE(Py_TYPE(op), nitems); PyGC_Head *g = AS_GC(op); if (basicsize > PY_SSIZE_T_MAX - sizeof(PyGC_Head)) return (PyVarObject *)PyErr_NoMemory(); g = (PyGC_Head *)PyObject_REALLOC(g, sizeof(PyGC_Head) + basicsize); if (g == NULL) return (PyVarObject *)PyErr_NoMemory(); op = (PyVarObject *) FROM_GC(g); Py_SIZE(op) = nitems; return op; } void PyObject_GC_Del(void *op) { PyGC_Head *g = AS_GC(op); if (IS_TRACKED(op)) gc_list_remove(g); if (_PyRuntime.gc.generations[0].count > 0) { _PyRuntime.gc.generations[0].count--; } PyObject_FREE(g); }