__attribute__((always_inline)) bool isWeaklyReferenced(Box* b) {
if (PyType_SUPPORTS_WEAKREFS(b->cls)) {
PyWeakReference** list = (PyWeakReference**)PyObject_GET_WEAKREFS_LISTPTR(b);
if (list && *list) {
return true;
}
}
return false;
}
void runCollection() {
static StatCounter sc("gc_collections");
sc.log();
ncollections++;
if (VERBOSITY("gc") >= 2)
printf("Collection #%d\n", ncollections);
Timer _t("collecting", /*min_usec=*/10000);
markPhase();
std::list<Box*, StlCompatAllocator<Box*>> weakly_referenced;
sweepPhase(weakly_referenced);
for (auto o : weakly_referenced) {
PyWeakReference** list = (PyWeakReference**)PyObject_GET_WEAKREFS_LISTPTR(o);
while (PyWeakReference* head = *list) {
assert(isValidGCObject(head));
if (head->wr_object != Py_None) {
_PyWeakref_ClearRef(head);
if (head->wr_callback) {
runtimeCall(head->wr_callback, ArgPassSpec(1), reinterpret_cast<Box*>(head), NULL, NULL, NULL,
NULL);
head->wr_callback = NULL;
}
}
}
}
if (VERBOSITY("gc") >= 2)
printf("Collection #%d done\n\n", ncollections);
long us = _t.end();
static StatCounter sc_us("gc_collections_us");
sc_us.log(us);
// dumpHeapStatistics();
}
__attribute__((always_inline)) bool _doFree(GCAllocation* al, std::vector<Box*>* weakly_referenced) {
#ifndef NVALGRIND
VALGRIND_DISABLE_ERROR_REPORTING;
#endif
GCKind alloc_kind = al->kind_id;
#ifndef NVALGRIND
VALGRIND_ENABLE_ERROR_REPORTING;
#endif
if (alloc_kind == GCKind::PYTHON || alloc_kind == GCKind::CONSERVATIVE_PYTHON) {
#ifndef NVALGRIND
VALGRIND_DISABLE_ERROR_REPORTING;
#endif
Box* b = (Box*)al->user_data;
#ifndef NVALGRIND
VALGRIND_ENABLE_ERROR_REPORTING;
#endif
if (PyType_SUPPORTS_WEAKREFS(b->cls)) {
PyWeakReference** list = (PyWeakReference**)PyObject_GET_WEAKREFS_LISTPTR(b);
if (list && *list) {
assert(weakly_referenced && "attempting to free a weakly referenced object manually");
weakly_referenced->push_back(b);
return false;
}
}
// XXX: we are currently ignoring destructors (tp_dealloc) for extension objects, since we have
// historically done that (whoops) and there are too many to be worth changing for now as long
// as we can get real destructor support soon.
ASSERT(b->cls->tp_dealloc == NULL || alloc_kind == GCKind::CONSERVATIVE_PYTHON, "%s", getTypeName(b));
if (b->cls->simple_destructor)
b->cls->simple_destructor(b);
}
return true;
}
bool _doFree(GCAllocation* al, std::list<Box*, StlCompatAllocator<Box*>>* weakly_referenced) {
if (VERBOSITY() >= 2)
printf("Freeing %p\n", al->user_data);
#ifndef NVALGRIND
VALGRIND_DISABLE_ERROR_REPORTING;
#endif
GCKind alloc_kind = al->kind_id;
#ifndef NVALGRIND
VALGRIND_ENABLE_ERROR_REPORTING;
#endif
if (alloc_kind == GCKind::PYTHON) {
#ifndef NVALGRIND
VALGRIND_DISABLE_ERROR_REPORTING;
#endif
Box* b = (Box*)al->user_data;
#ifndef NVALGRIND
VALGRIND_ENABLE_ERROR_REPORTING;
#endif
if (PyType_SUPPORTS_WEAKREFS(b->cls)) {
PyWeakReference** list = (PyWeakReference**)PyObject_GET_WEAKREFS_LISTPTR(b);
if (list && *list) {
assert(weakly_referenced && "attempting to free a weakly referenced object manually");
weakly_referenced->push_back(b);
return false;
}
}
ASSERT(b->cls->tp_dealloc == NULL, "%s", getTypeName(b));
if (b->cls->simple_destructor)
b->cls->simple_destructor(b);
}
return true;
}
/* 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;
}
