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/*
Reference Cycle Garbage Collection
==================================
Neil Schemenauer <nas@arctrix.com>
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/context.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);
struct gc_generation permanent_generation = {
{{&state->permanent_generation.head, &state->permanent_generation.head, 0}}, 0, 0
};
state->permanent_generation = permanent_generation;
}
/*--------------------------------------------------------------------------
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();
(void)PyContext_ClearFreeList();
}
/* 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)));
PySys_WriteStderr("\ngc: objects in permanent generation: %zd",
gc_list_size(&_PyRuntime.gc.permanent_generation.head));
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<PyList_GET_SIZE(_PyRuntime.gc.callbacks); i++) {
PyObject *r, *cb = PyList_GET_ITEM(_PyRuntime.gc.callbacks, i);
Py_INCREF(cb); /* make sure cb doesn't go away */
r = PyObject_CallFunction(cb, "sO", phase, info);
Py_XDECREF(r);
if (r == NULL)
PyErr_WriteUnraisable(cb);
Py_DECREF(cb);
}
Py_XDECREF(info);
}
/* Perform garbage collection of a generation and invoke
* progress callbacks.
*/
static Py_ssize_t
collect_with_callback(int generation)
{
Py_ssize_t result, collected, uncollectable;
invoke_gc_callback("start", generation, 0, 0);
result = collect(generation, &collected, &uncollectable, 0);
invoke_gc_callback("stop", generation, collected, uncollectable);
return result;
}
static Py_ssize_t
collect_generations(void)
{
int i;
Py_ssize_t n = 0;
/* Find the oldest generation (highest numbered) where the count
* exceeds the threshold. Objects in the that generation and
* generations younger than it will be collected. */
for (i = NUM_GENERATIONS-1; 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;
}
/*[clinic input]
gc.freeze
Freeze all current tracked objects and ignore them for future collections.
This can be used before a POSIX fork() call to make the gc copy-on-write friendly.
Note: collection before a POSIX fork() call may free pages for future allocation
which can cause copy-on-write.
[clinic start generated code]*/
static PyObject *
gc_freeze_impl(PyObject *module)
/*[clinic end generated code: output=502159d9cdc4c139 input=b602b16ac5febbe5]*/
{
for (int i = 0; i < NUM_GENERATIONS; ++i) {
gc_list_merge(GEN_HEAD(i), &_PyRuntime.gc.permanent_generation.head);
_PyRuntime.gc.generations[i].count = 0;
}
Py_RETURN_NONE;
}
/*[clinic input]
gc.unfreeze
Unfreeze all objects in the permanent generation.
Put all objects in the permanent generation back into oldest generation.
[clinic start generated code]*/
static PyObject *
gc_unfreeze_impl(PyObject *module)
/*[clinic end generated code: output=1c15f2043b25e169 input=2dd52b170f4cef6c]*/
{
gc_list_merge(&_PyRuntime.gc.permanent_generation.head, GEN_HEAD(NUM_GENERATIONS-1));
Py_RETURN_NONE;
}
/*[clinic input]
gc.get_freeze_count -> Py_ssize_t
Return the number of objects in the permanent generation.
[clinic start generated code]*/
static Py_ssize_t
gc_get_freeze_count_impl(PyObject *module)
/*[clinic end generated code: output=61cbd9f43aa032e1 input=45ffbc65cfe2a6ed]*/
{
return gc_list_size(&_PyRuntime.gc.permanent_generation.head);
}
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"
"freeze() -- Freeze all tracked objects and ignore them for future collections.\n"
"unfreeze() -- Unfreeze all objects in the permanent generation.\n"
"get_freeze_count() -- Return the number of objects in the permanent generation.\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__},
GC_FREEZE_METHODDEF
GC_UNFREEZE_METHODDEF
GC_GET_FREEZE_COUNT_METHODDEF
{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) {
const 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);
assert(!IS_TRACKED(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);
}
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