void PyObject_GC_Del(void *op) { PyGC_Head *g = AS_GC(op); if (IS_TRACKED(op)) gc_list_remove(g); if (generations[0].count > 0) { generations[0].count--; } PyObject_FREE(g); }
/* A traversal callback for move_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); gc->gc.gc_refs = GC_REACHABLE; } } return 0; }
PyVarObject * _PyObject_GC_Resize(PyVarObject *op, int nitems) { const size_t basicsize = _PyObject_VAR_SIZE(op->ob_type, nitems); PyGC_Head *g = AS_GC(op); g = PyObject_REALLOC(g, sizeof(PyGC_Head) + basicsize); if (g == NULL) return (PyVarObject *)PyErr_NoMemory(); op = (PyVarObject *) FROM_GC(g); op->ob_size = 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; }
/* 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(gc->gc.gc_refs != 0); /* else refcount was too small */ if (gc->gc.gc_refs > 0) gc->gc.gc_refs--; } return 0; }
/* 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 int gc_refs = gc->gc.gc_refs; 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. */ gc->gc.gc_refs = 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); gc->gc.gc_refs = 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; }
/* 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(op->ob_type)) 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_CallFunction(callback, "O", wr); 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; }