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cpython/Python/gc_free_threading.c
Miss Islington (bot) 0794220a69
[3.13] gh-121794: Don't set ob_tid to zero in fast-path dealloc (GH-121799) (#121821) 
We should maintain the invariant that a zero `ob_tid` implies the
refcount fields are merged.

* Move the assignment in `_Py_MergeZeroLocalRefcount` to immediately
  before the refcount merge.
* Update `_PyTrash_thread_destroy_chain` to set `ob_ref_shared` to
  `_Py_REF_MERGED` when setting `ob_tid` to zero.

Also check this invariant with assertions in the GC in debug builds.
That uncovered a bug when running out of memory during GC.
(cherry picked from commit d23be3947c)

Co-authored-by: Sam Gross <colesbury@gmail.com>
2024-07-15 22:15:23 +00:00

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// Cyclic garbage collector implementation for free-threaded build.
#include "Python.h"
#include "pycore_brc.h" // struct _brc_thread_state
#include "pycore_ceval.h" // _Py_set_eval_breaker_bit()
#include "pycore_context.h"
#include "pycore_dict.h" // _PyDict_MaybeUntrack()
#include "pycore_initconfig.h"
#include "pycore_interp.h" // PyInterpreterState.gc
#include "pycore_object.h"
#include "pycore_object_alloc.h" // _PyObject_MallocWithType()
#include "pycore_object_stack.h"
#include "pycore_pyerrors.h"
#include "pycore_pystate.h" // _PyThreadState_GET()
#include "pycore_tstate.h" // _PyThreadStateImpl
#include "pycore_weakref.h" // _PyWeakref_ClearRef()
#include "pydtrace.h"
#ifdef Py_GIL_DISABLED
typedef struct _gc_runtime_state GCState;
#ifdef Py_DEBUG
# define GC_DEBUG
#endif
// Each thread buffers the count of allocated objects in a thread-local
// variable up to +/- this amount to reduce the overhead of updating
// the global count.
#define LOCAL_ALLOC_COUNT_THRESHOLD 512
// Automatically choose the generation that needs collecting.
#define GENERATION_AUTO (-1)
// A linked list of objects using the `ob_tid` field as the next pointer.
// The linked list pointers are distinct from any real thread ids, because the
// thread ids returned by _Py_ThreadId() are also pointers to distinct objects.
// No thread will confuse its own id with a linked list pointer.
struct worklist {
uintptr_t head;
};
struct worklist_iter {
uintptr_t *ptr; // pointer to current object
uintptr_t *next; // next value of ptr
};
struct visitor_args {
size_t offset; // offset of PyObject from start of block
};
// Per-collection state
struct collection_state {
struct visitor_args base;
PyInterpreterState *interp;
GCState *gcstate;
Py_ssize_t collected;
Py_ssize_t uncollectable;
Py_ssize_t long_lived_total;
struct worklist unreachable;
struct worklist legacy_finalizers;
struct worklist wrcb_to_call;
struct worklist objs_to_decref;
};
// iterate over a worklist
#define WORKSTACK_FOR_EACH(stack, op) \
for ((op) = (PyObject *)(stack)->head; (op) != NULL; (op) = (PyObject *)(op)->ob_tid)
// iterate over a worklist with support for removing the current object
#define WORKSTACK_FOR_EACH_ITER(stack, iter, op) \
for (worklist_iter_init((iter), &(stack)->head), (op) = (PyObject *)(*(iter)->ptr); \
(op) != NULL; \
worklist_iter_init((iter), (iter)->next), (op) = (PyObject *)(*(iter)->ptr))
static void
worklist_push(struct worklist *worklist, PyObject *op)
{
assert(op->ob_tid == 0);
op->ob_tid = worklist->head;
worklist->head = (uintptr_t)op;
}
static PyObject *
worklist_pop(struct worklist *worklist)
{
PyObject *op = (PyObject *)worklist->head;
if (op != NULL) {
worklist->head = op->ob_tid;
_Py_atomic_store_uintptr_relaxed(&op->ob_tid, 0);
}
return op;
}
static void
worklist_iter_init(struct worklist_iter *iter, uintptr_t *next)
{
iter->ptr = next;
PyObject *op = (PyObject *)*(iter->ptr);
if (op) {
iter->next = &op->ob_tid;
}
}
static void
worklist_remove(struct worklist_iter *iter)
{
PyObject *op = (PyObject *)*(iter->ptr);
*(iter->ptr) = op->ob_tid;
op->ob_tid = 0;
iter->next = iter->ptr;
}
static inline int
gc_is_unreachable(PyObject *op)
{
return (op->ob_gc_bits & _PyGC_BITS_UNREACHABLE) != 0;
}
static void
gc_set_unreachable(PyObject *op)
{
op->ob_gc_bits |= _PyGC_BITS_UNREACHABLE;
}
static void
gc_clear_unreachable(PyObject *op)
{
op->ob_gc_bits &= ~_PyGC_BITS_UNREACHABLE;
}
// Initialize the `ob_tid` field to zero if the object is not already
// initialized as unreachable.
static void
gc_maybe_init_refs(PyObject *op)
{
if (!gc_is_unreachable(op)) {
gc_set_unreachable(op);
op->ob_tid = 0;
}
}
static inline Py_ssize_t
gc_get_refs(PyObject *op)
{
return (Py_ssize_t)op->ob_tid;
}
static inline void
gc_add_refs(PyObject *op, Py_ssize_t refs)
{
assert(_PyObject_GC_IS_TRACKED(op));
op->ob_tid += refs;
}
static inline void
gc_decref(PyObject *op)
{
op->ob_tid -= 1;
}
static void
disable_deferred_refcounting(PyObject *op)
{
if (_PyObject_HasDeferredRefcount(op)) {
op->ob_gc_bits &= ~_PyGC_BITS_DEFERRED;
op->ob_ref_shared -= (1 << _Py_REF_SHARED_SHIFT);
}
}
static Py_ssize_t
merge_refcount(PyObject *op, Py_ssize_t extra)
{
assert(_PyInterpreterState_GET()->stoptheworld.world_stopped);
Py_ssize_t refcount = Py_REFCNT(op);
refcount += extra;
#ifdef Py_REF_DEBUG
_Py_AddRefTotal(_PyThreadState_GET(), extra);
#endif
// No atomics necessary; all other threads in this interpreter are paused.
op->ob_tid = 0;
op->ob_ref_local = 0;
op->ob_ref_shared = _Py_REF_SHARED(refcount, _Py_REF_MERGED);
return refcount;
}
static void
gc_restore_tid(PyObject *op)
{
assert(_PyInterpreterState_GET()->stoptheworld.world_stopped);
mi_segment_t *segment = _mi_ptr_segment(op);
if (_Py_REF_IS_MERGED(op->ob_ref_shared)) {
op->ob_tid = 0;
}
else {
// NOTE: may change ob_tid if the object was re-initialized by
// a different thread or its segment was abandoned and reclaimed.
// The segment thread id might be zero, in which case we should
// ensure the refcounts are now merged.
op->ob_tid = segment->thread_id;
if (op->ob_tid == 0) {
merge_refcount(op, 0);
}
}
}
static void
gc_restore_refs(PyObject *op)
{
if (gc_is_unreachable(op)) {
gc_restore_tid(op);
gc_clear_unreachable(op);
}
}
// Given a mimalloc memory block return the PyObject stored in it or NULL if
// the block is not allocated or the object is not tracked or is immortal.
static PyObject *
op_from_block(void *block, void *arg, bool include_frozen)
{
struct visitor_args *a = arg;
if (block == NULL) {
return NULL;
}
PyObject *op = (PyObject *)((char*)block + a->offset);
assert(PyObject_IS_GC(op));
if (!_PyObject_GC_IS_TRACKED(op)) {
return NULL;
}
if (!include_frozen && (op->ob_gc_bits & _PyGC_BITS_FROZEN) != 0) {
return NULL;
}
return op;
}
static int
gc_visit_heaps_lock_held(PyInterpreterState *interp, mi_block_visit_fun *visitor,
struct visitor_args *arg)
{
// Offset of PyObject header from start of memory block.
Py_ssize_t offset_base = 0;
if (_PyMem_DebugEnabled()) {
// The debug allocator adds two words at the beginning of each block.
offset_base += 2 * sizeof(size_t);
}
// Objects with Py_TPFLAGS_PREHEADER have two extra fields
Py_ssize_t offset_pre = offset_base + 2 * sizeof(PyObject*);
// visit each thread's heaps for GC objects
for (PyThreadState *p = interp->threads.head; p != NULL; p = p->next) {
struct _mimalloc_thread_state *m = &((_PyThreadStateImpl *)p)->mimalloc;
if (!_Py_atomic_load_int(&m->initialized)) {
// The thread may not have called tstate_mimalloc_bind() yet.
continue;
}
arg->offset = offset_base;
if (!mi_heap_visit_blocks(&m->heaps[_Py_MIMALLOC_HEAP_GC], true,
visitor, arg)) {
return -1;
}
arg->offset = offset_pre;
if (!mi_heap_visit_blocks(&m->heaps[_Py_MIMALLOC_HEAP_GC_PRE], true,
visitor, arg)) {
return -1;
}
}
// visit blocks in the per-interpreter abandoned pool (from dead threads)
mi_abandoned_pool_t *pool = &interp->mimalloc.abandoned_pool;
arg->offset = offset_base;
if (!_mi_abandoned_pool_visit_blocks(pool, _Py_MIMALLOC_HEAP_GC, true,
visitor, arg)) {
return -1;
}
arg->offset = offset_pre;
if (!_mi_abandoned_pool_visit_blocks(pool, _Py_MIMALLOC_HEAP_GC_PRE, true,
visitor, arg)) {
return -1;
}
return 0;
}
// Visits all GC objects in the interpreter's heaps.
// NOTE: It is not safe to allocate or free any mimalloc managed memory while
// this function is running.
static int
gc_visit_heaps(PyInterpreterState *interp, mi_block_visit_fun *visitor,
struct visitor_args *arg)
{
// Other threads in the interpreter must be paused so that we can safely
// traverse their heaps.
assert(interp->stoptheworld.world_stopped);
int err;
HEAD_LOCK(&_PyRuntime);
err = gc_visit_heaps_lock_held(interp, visitor, arg);
HEAD_UNLOCK(&_PyRuntime);
return err;
}
static void
merge_queued_objects(_PyThreadStateImpl *tstate, struct collection_state *state)
{
struct _brc_thread_state *brc = &tstate->brc;
_PyObjectStack_Merge(&brc->local_objects_to_merge, &brc->objects_to_merge);
PyObject *op;
while ((op = _PyObjectStack_Pop(&brc->local_objects_to_merge)) != NULL) {
// Subtract one when merging because the queue had a reference.
Py_ssize_t refcount = merge_refcount(op, -1);
if (!_PyObject_GC_IS_TRACKED(op) && refcount == 0) {
// GC objects with zero refcount are handled subsequently by the
// GC as if they were cyclic trash, but we have to handle dead
// non-GC objects here. Add one to the refcount so that we can
// decref and deallocate the object once we start the world again.
op->ob_ref_shared += (1 << _Py_REF_SHARED_SHIFT);
#ifdef Py_REF_DEBUG
_Py_IncRefTotal(_PyThreadState_GET());
#endif
worklist_push(&state->objs_to_decref, op);
}
}
}
static void
merge_all_queued_objects(PyInterpreterState *interp, struct collection_state *state)
{
HEAD_LOCK(&_PyRuntime);
for (PyThreadState *p = interp->threads.head; p != NULL; p = p->next) {
merge_queued_objects((_PyThreadStateImpl *)p, state);
}
HEAD_UNLOCK(&_PyRuntime);
}
static void
process_delayed_frees(PyInterpreterState *interp)
{
// In STW status, we can observe the latest write sequence by
// advancing the write sequence immediately.
_Py_qsbr_advance(&interp->qsbr);
_PyThreadStateImpl *current_tstate = (_PyThreadStateImpl *)_PyThreadState_GET();
_Py_qsbr_quiescent_state(current_tstate->qsbr);
HEAD_LOCK(&_PyRuntime);
PyThreadState *tstate = interp->threads.head;
while (tstate != NULL) {
_PyMem_ProcessDelayed(tstate);
tstate = (PyThreadState *)tstate->next;
}
HEAD_UNLOCK(&_PyRuntime);
}
// Subtract an incoming reference from the computed "gc_refs" refcount.
static int
visit_decref(PyObject *op, void *arg)
{
if (_PyObject_GC_IS_TRACKED(op) && !_Py_IsImmortal(op)) {
// If update_refs hasn't reached this object yet, mark it
// as (tentatively) unreachable and initialize ob_tid to zero.
gc_maybe_init_refs(op);
gc_decref(op);
}
return 0;
}
// Compute the number of external references to objects in the heap
// by subtracting internal references from the refcount. The difference is
// computed in the ob_tid field (we restore it later).
static bool
update_refs(const mi_heap_t *heap, const mi_heap_area_t *area,
void *block, size_t block_size, void *args)
{
PyObject *op = op_from_block(block, args, false);
if (op == NULL) {
return true;
}
// Exclude immortal objects from garbage collection
if (_Py_IsImmortal(op)) {
op->ob_tid = 0;
_PyObject_GC_UNTRACK(op);
gc_clear_unreachable(op);
return true;
}
Py_ssize_t refcount = Py_REFCNT(op);
refcount -= _PyObject_HasDeferredRefcount(op);
_PyObject_ASSERT(op, refcount >= 0);
if (refcount > 0 && !_PyObject_HasDeferredRefcount(op)) {
// Untrack tuples and dicts as necessary in this pass, but not objects
// with zero refcount, which we will want to collect.
if (PyTuple_CheckExact(op)) {
_PyTuple_MaybeUntrack(op);
if (!_PyObject_GC_IS_TRACKED(op)) {
gc_restore_refs(op);
return true;
}
}
else if (PyDict_CheckExact(op)) {
_PyDict_MaybeUntrack(op);
if (!_PyObject_GC_IS_TRACKED(op)) {
gc_restore_refs(op);
return true;
}
}
}
// We repurpose ob_tid to compute "gc_refs", the number of external
// references to the object (i.e., from outside the GC heaps). This means
// that ob_tid is no longer a valid thread id until it is restored by
// scan_heap_visitor(). Until then, we cannot use the standard reference
// counting functions or allow other threads to run Python code.
gc_maybe_init_refs(op);
// Add the actual refcount to ob_tid.
gc_add_refs(op, refcount);
// Subtract internal references from ob_tid. Objects with ob_tid > 0
// are directly reachable from outside containers, and so can't be
// collected.
Py_TYPE(op)->tp_traverse(op, visit_decref, NULL);
return true;
}
static int
visit_clear_unreachable(PyObject *op, _PyObjectStack *stack)
{
if (gc_is_unreachable(op)) {
_PyObject_ASSERT(op, _PyObject_GC_IS_TRACKED(op));
gc_clear_unreachable(op);
return _PyObjectStack_Push(stack, op);
}
return 0;
}
// Transitively clear the unreachable bit on all objects reachable from op.
static int
mark_reachable(PyObject *op)
{
_PyObjectStack stack = { NULL };
do {
traverseproc traverse = Py_TYPE(op)->tp_traverse;
if (traverse(op, (visitproc)&visit_clear_unreachable, &stack) < 0) {
_PyObjectStack_Clear(&stack);
return -1;
}
op = _PyObjectStack_Pop(&stack);
} while (op != NULL);
return 0;
}
#ifdef GC_DEBUG
static bool
validate_refcounts(const mi_heap_t *heap, const mi_heap_area_t *area,
void *block, size_t block_size, void *args)
{
PyObject *op = op_from_block(block, args, false);
if (op == NULL) {
return true;
}
_PyObject_ASSERT_WITH_MSG(op, !gc_is_unreachable(op),
"object should not be marked as unreachable yet");
if (_Py_REF_IS_MERGED(op->ob_ref_shared)) {
_PyObject_ASSERT_WITH_MSG(op, op->ob_tid == 0,
"merged objects should have ob_tid == 0");
}
else if (!_Py_IsImmortal(op)) {
_PyObject_ASSERT_WITH_MSG(op, op->ob_tid != 0,
"unmerged objects should have ob_tid != 0");
}
return true;
}
static bool
validate_gc_objects(const mi_heap_t *heap, const mi_heap_area_t *area,
void *block, size_t block_size, void *args)
{
PyObject *op = op_from_block(block, args, false);
if (op == NULL) {
return true;
}
_PyObject_ASSERT(op, gc_is_unreachable(op));
_PyObject_ASSERT_WITH_MSG(op, gc_get_refs(op) >= 0,
"refcount is too small");
return true;
}
#endif
static bool
mark_heap_visitor(const mi_heap_t *heap, const mi_heap_area_t *area,
void *block, size_t block_size, void *args)
{
PyObject *op = op_from_block(block, args, false);
if (op == NULL) {
return true;
}
_PyObject_ASSERT_WITH_MSG(op, gc_get_refs(op) >= 0,
"refcount is too small");
if (gc_is_unreachable(op) && gc_get_refs(op) != 0) {
// Object is reachable but currently marked as unreachable.
// Mark it as reachable and traverse its pointers to find
// any other object that may be directly reachable from it.
gc_clear_unreachable(op);
// Transitively mark reachable objects by clearing the unreachable flag.
if (mark_reachable(op) < 0) {
return false;
}
}
return true;
}
static bool
restore_refs(const mi_heap_t *heap, const mi_heap_area_t *area,
void *block, size_t block_size, void *args)
{
PyObject *op = op_from_block(block, args, false);
if (op == NULL) {
return true;
}
gc_restore_tid(op);
gc_clear_unreachable(op);
return true;
}
/* Return true if object has a pre-PEP 442 finalization method. */
static int
has_legacy_finalizer(PyObject *op)
{
return Py_TYPE(op)->tp_del != NULL;
}
static bool
scan_heap_visitor(const mi_heap_t *heap, const mi_heap_area_t *area,
void *block, size_t block_size, void *args)
{
PyObject *op = op_from_block(block, args, false);
if (op == NULL) {
return true;
}
struct collection_state *state = (struct collection_state *)args;
if (gc_is_unreachable(op)) {
// Disable deferred refcounting for unreachable objects so that they
// are collected immediately after finalization.
disable_deferred_refcounting(op);
// Merge and add one to the refcount to prevent deallocation while we
// are holding on to it in a worklist.
merge_refcount(op, 1);
if (has_legacy_finalizer(op)) {
// would be unreachable, but has legacy finalizer
gc_clear_unreachable(op);
worklist_push(&state->legacy_finalizers, op);
}
else {
worklist_push(&state->unreachable, op);
}
}
else {
// object is reachable, restore `ob_tid`; we're done with these objects
gc_restore_tid(op);
state->long_lived_total++;
}
return true;
}
static int
move_legacy_finalizer_reachable(struct collection_state *state);
static int
deduce_unreachable_heap(PyInterpreterState *interp,
struct collection_state *state)
{
#ifdef GC_DEBUG
// Check that all objects are marked as unreachable and that the computed
// reference count difference (stored in `ob_tid`) is non-negative.
gc_visit_heaps(interp, &validate_refcounts, &state->base);
#endif
// Identify objects that are directly reachable from outside the GC heap
// by computing the difference between the refcount and the number of
// incoming references.
gc_visit_heaps(interp, &update_refs, &state->base);
#ifdef GC_DEBUG
// Check that all objects are marked as unreachable and that the computed
// reference count difference (stored in `ob_tid`) is non-negative.
gc_visit_heaps(interp, &validate_gc_objects, &state->base);
#endif
// Transitively mark reachable objects by clearing the
// _PyGC_BITS_UNREACHABLE flag.
if (gc_visit_heaps(interp, &mark_heap_visitor, &state->base) < 0) {
// On out-of-memory, restore the refcounts and bail out.
gc_visit_heaps(interp, &restore_refs, &state->base);
return -1;
}
// Identify remaining unreachable objects and push them onto a stack.
// Restores ob_tid for reachable objects.
gc_visit_heaps(interp, &scan_heap_visitor, &state->base);
if (state->legacy_finalizers.head) {
// There may be objects reachable from legacy finalizers that are in
// the unreachable set. We need to mark them as reachable.
if (move_legacy_finalizer_reachable(state) < 0) {
return -1;
}
}
return 0;
}
static int
move_legacy_finalizer_reachable(struct collection_state *state)
{
// Clear the reachable bit on all objects transitively reachable
// from the objects with legacy finalizers.
PyObject *op;
WORKSTACK_FOR_EACH(&state->legacy_finalizers, op) {
if (mark_reachable(op) < 0) {
return -1;
}
}
// Move the reachable objects from the unreachable worklist to the legacy
// finalizer worklist.
struct worklist_iter iter;
WORKSTACK_FOR_EACH_ITER(&state->unreachable, &iter, op) {
if (!gc_is_unreachable(op)) {
worklist_remove(&iter);
worklist_push(&state->legacy_finalizers, op);
}
}
return 0;
}
// Clear all weakrefs to unreachable objects. Weakrefs with callbacks are
// enqueued in `wrcb_to_call`, but not invoked yet.
static void
clear_weakrefs(struct collection_state *state)
{
PyObject *op;
WORKSTACK_FOR_EACH(&state->unreachable, op) {
if (PyWeakref_Check(op)) {
// Clear weakrefs that are themselves unreachable to ensure their
// callbacks will not be executed later from a `tp_clear()`
// inside delete_garbage(). That would be unsafe: it could
// resurrect a dead object or access a an already cleared object.
// See bpo-38006 for one example.
_PyWeakref_ClearRef((PyWeakReference *)op);
}
if (!_PyType_SUPPORTS_WEAKREFS(Py_TYPE(op))) {
continue;
}
// NOTE: This is never triggered for static types so we can avoid the
// (slightly) more costly _PyObject_GET_WEAKREFS_LISTPTR().
PyWeakReference **wrlist = _PyObject_GET_WEAKREFS_LISTPTR_FROM_OFFSET(op);
// `op` may have some weakrefs. March over the list, clear
// all the weakrefs, and enqueue the weakrefs with callbacks
// that must be called into wrcb_to_call.
for (PyWeakReference *wr = *wrlist; wr != NULL; wr = *wrlist) {
// _PyWeakref_ClearRef clears the weakref but leaves
// the callback pointer intact. Obscure: it also
// changes *wrlist.
_PyObject_ASSERT((PyObject *)wr, wr->wr_object == op);
_PyWeakref_ClearRef(wr);
_PyObject_ASSERT((PyObject *)wr, wr->wr_object == Py_None);
// We do not invoke callbacks for weakrefs that are themselves
// unreachable. This is partly for historical reasons: weakrefs
// predate safe object finalization, and a weakref that is itself
// unreachable may have a callback that resurrects other
// unreachable objects.
if (wr->wr_callback == NULL || gc_is_unreachable((PyObject *)wr)) {
continue;
}
// Create a new reference so that wr can't go away before we can
// process it again.
merge_refcount((PyObject *)wr, 1);
// Enqueue weakref to be called later.
worklist_push(&state->wrcb_to_call, (PyObject *)wr);
}
}
}
static void
call_weakref_callbacks(struct collection_state *state)
{
// Invoke the callbacks we decided to honor.
PyObject *op;
while ((op = worklist_pop(&state->wrcb_to_call)) != NULL) {
_PyObject_ASSERT(op, PyWeakref_Check(op));
PyWeakReference *wr = (PyWeakReference *)op;
PyObject *callback = wr->wr_callback;
_PyObject_ASSERT(op, callback != NULL);
/* copy-paste of weakrefobject.c's handle_callback() */
PyObject *temp = PyObject_CallOneArg(callback, (PyObject *)wr);
if (temp == NULL) {
PyErr_WriteUnraisable(callback);
}
else {
Py_DECREF(temp);
}
Py_DECREF(op); // drop worklist reference
}
}
static GCState *
get_gc_state(void)
{
PyInterpreterState *interp = _PyInterpreterState_GET();
return &interp->gc;
}
void
_PyGC_InitState(GCState *gcstate)
{
// TODO: move to pycore_runtime_init.h once the incremental GC lands.
gcstate->young.threshold = 2000;
}
PyStatus
_PyGC_Init(PyInterpreterState *interp)
{
GCState *gcstate = &interp->gc;
// gh-117783: immortalize objects that would use deferred refcounting
// once the first non-main thread is created (but not in subinterpreters).
gcstate->immortalize = _Py_IsMainInterpreter(interp) ? 0 : -1;
gcstate->garbage = PyList_New(0);
if (gcstate->garbage == NULL) {
return _PyStatus_NO_MEMORY();
}
gcstate->callbacks = PyList_New(0);
if (gcstate->callbacks == NULL) {
return _PyStatus_NO_MEMORY();
}
return _PyStatus_OK();
}
static void
debug_cycle(const char *msg, PyObject *op)
{
PySys_FormatStderr("gc: %s <%s %p>\n",
msg, Py_TYPE(op)->tp_name, op);
}
/* 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(struct collection_state *state)
{
// NOTE: the unreachable worklist holds a strong reference to the object
// to prevent it from being deallocated while we are holding on to it.
PyObject *op;
WORKSTACK_FOR_EACH(&state->unreachable, op) {
if (!_PyGC_FINALIZED(op)) {
destructor finalize = Py_TYPE(op)->tp_finalize;
if (finalize != NULL) {
_PyGC_SET_FINALIZED(op);
finalize(op);
assert(!_PyErr_Occurred(_PyThreadState_GET()));
}
}
}
}
// Break reference cycles by clearing the containers involved.
static void
delete_garbage(struct collection_state *state)
{
PyThreadState *tstate = _PyThreadState_GET();
GCState *gcstate = state->gcstate;
assert(!_PyErr_Occurred(tstate));
PyObject *op;
while ((op = worklist_pop(&state->objs_to_decref)) != NULL) {
Py_DECREF(op);
}
while ((op = worklist_pop(&state->unreachable)) != NULL) {
_PyObject_ASSERT(op, gc_is_unreachable(op));
// Clear the unreachable flag.
gc_clear_unreachable(op);
if (!_PyObject_GC_IS_TRACKED(op)) {
// Object might have been untracked by some other tp_clear() call.
Py_DECREF(op); // drop the reference from the worklist
continue;
}
state->collected++;
if (gcstate->debug & _PyGC_DEBUG_SAVEALL) {
assert(gcstate->garbage != NULL);
if (PyList_Append(gcstate->garbage, op) < 0) {
_PyErr_Clear(tstate);
}
}
else {
inquiry clear = Py_TYPE(op)->tp_clear;
if (clear != NULL) {
(void) clear(op);
if (_PyErr_Occurred(tstate)) {
PyErr_FormatUnraisable("Exception ignored in tp_clear of %s",
Py_TYPE(op)->tp_name);
}
}
}
Py_DECREF(op); // drop the reference from the worklist
}
}
static void
handle_legacy_finalizers(struct collection_state *state)
{
GCState *gcstate = state->gcstate;
assert(gcstate->garbage != NULL);
PyObject *op;
while ((op = worklist_pop(&state->legacy_finalizers)) != NULL) {
state->uncollectable++;
if (gcstate->debug & _PyGC_DEBUG_UNCOLLECTABLE) {
debug_cycle("uncollectable", op);
}
if ((gcstate->debug & _PyGC_DEBUG_SAVEALL) || has_legacy_finalizer(op)) {
if (PyList_Append(gcstate->garbage, op) < 0) {
PyErr_Clear();
}
}
Py_DECREF(op); // drop worklist reference
}
}
// Show stats for objects in each generations
static void
show_stats_each_generations(GCState *gcstate)
{
// TODO
}
// Traversal callback for handle_resurrected_objects.
static int
visit_decref_unreachable(PyObject *op, void *data)
{
if (gc_is_unreachable(op) && _PyObject_GC_IS_TRACKED(op)) {
op->ob_ref_local -= 1;
}
return 0;
}
// Handle objects that may have resurrected after a call to 'finalize_garbage'.
static int
handle_resurrected_objects(struct collection_state *state)
{
// First, find externally reachable objects by computing the reference
// count difference in ob_ref_local. We can't use ob_tid here because
// that's already used to store the unreachable worklist.
PyObject *op;
struct worklist_iter iter;
WORKSTACK_FOR_EACH_ITER(&state->unreachable, &iter, op) {
assert(gc_is_unreachable(op));
assert(_Py_REF_IS_MERGED(op->ob_ref_shared));
if (!_PyObject_GC_IS_TRACKED(op)) {
// Object was untracked by a finalizer. Schedule it for a Py_DECREF
// after we finish with the stop-the-world pause.
gc_clear_unreachable(op);
worklist_remove(&iter);
worklist_push(&state->objs_to_decref, op);
continue;
}
Py_ssize_t refcount = (op->ob_ref_shared >> _Py_REF_SHARED_SHIFT);
if (refcount > INT32_MAX) {
// The refcount is too big to fit in `ob_ref_local`. Mark the
// object as immortal and bail out.
gc_clear_unreachable(op);
worklist_remove(&iter);
_Py_SetImmortal(op);
continue;
}
op->ob_ref_local += (uint32_t)refcount;
// Subtract one to account for the reference from the worklist.
op->ob_ref_local -= 1;
traverseproc traverse = Py_TYPE(op)->tp_traverse;
(void) traverse(op,
(visitproc)visit_decref_unreachable,
NULL);
}
// Find resurrected objects
bool any_resurrected = false;
WORKSTACK_FOR_EACH(&state->unreachable, op) {
int32_t gc_refs = (int32_t)op->ob_ref_local;
op->ob_ref_local = 0; // restore ob_ref_local
_PyObject_ASSERT(op, gc_refs >= 0);
if (gc_is_unreachable(op) && gc_refs > 0) {
// Clear the unreachable flag on any transitively reachable objects
// from this one.
any_resurrected = true;
gc_clear_unreachable(op);
if (mark_reachable(op) < 0) {
return -1;
}
}
}
if (any_resurrected) {
// Remove resurrected objects from the unreachable list.
WORKSTACK_FOR_EACH_ITER(&state->unreachable, &iter, op) {
if (!gc_is_unreachable(op)) {
_PyObject_ASSERT(op, Py_REFCNT(op) > 1);
worklist_remove(&iter);
merge_refcount(op, -1); // remove worklist reference
}
}
}
#ifdef GC_DEBUG
WORKSTACK_FOR_EACH(&state->unreachable, op) {
_PyObject_ASSERT(op, gc_is_unreachable(op));
_PyObject_ASSERT(op, _PyObject_GC_IS_TRACKED(op));
_PyObject_ASSERT(op, op->ob_ref_local == 0);
_PyObject_ASSERT(op, _Py_REF_IS_MERGED(op->ob_ref_shared));
}
#endif
return 0;
}
/* Invoke progress callbacks to notify clients that garbage collection
* is starting or stopping
*/
static void
invoke_gc_callback(PyThreadState *tstate, const char *phase,
int generation, Py_ssize_t collected,
Py_ssize_t uncollectable)
{
assert(!_PyErr_Occurred(tstate));
/* we may get called very early */
GCState *gcstate = &tstate->interp->gc;
if (gcstate->callbacks == NULL) {
return;
}
/* The local variable cannot be rebound, check it for sanity */
assert(PyList_CheckExact(gcstate->callbacks));
PyObject *info = NULL;
if (PyList_GET_SIZE(gcstate->callbacks) != 0) {
info = Py_BuildValue("{sisnsn}",
"generation", generation,
"collected", collected,
"uncollectable", uncollectable);
if (info == NULL) {
PyErr_FormatUnraisable("Exception ignored on invoking gc callbacks");
return;
}
}
PyObject *phase_obj = PyUnicode_FromString(phase);
if (phase_obj == NULL) {
Py_XDECREF(info);
PyErr_FormatUnraisable("Exception ignored on invoking gc callbacks");
return;
}
PyObject *stack[] = {phase_obj, info};
for (Py_ssize_t i=0; i<PyList_GET_SIZE(gcstate->callbacks); i++) {
PyObject *r, *cb = PyList_GET_ITEM(gcstate->callbacks, i);
Py_INCREF(cb); /* make sure cb doesn't go away */
r = PyObject_Vectorcall(cb, stack, 2, NULL);
if (r == NULL) {
PyErr_WriteUnraisable(cb);
}
else {
Py_DECREF(r);
}
Py_DECREF(cb);
}
Py_DECREF(phase_obj);
Py_XDECREF(info);
assert(!_PyErr_Occurred(tstate));
}
static void
cleanup_worklist(struct worklist *worklist)
{
PyObject *op;
while ((op = worklist_pop(worklist)) != NULL) {
gc_clear_unreachable(op);
Py_DECREF(op);
}
}
static bool
gc_should_collect(GCState *gcstate)
{
int count = _Py_atomic_load_int_relaxed(&gcstate->young.count);
int threshold = gcstate->young.threshold;
if (count <= threshold || threshold == 0 || !gcstate->enabled) {
return false;
}
// Avoid quadratic behavior by scaling threshold to the number of live
// objects. A few tests rely on immediate scheduling of the GC so we ignore
// the scaled threshold if generations[1].threshold is set to zero.
return (count > gcstate->long_lived_total / 4 ||
gcstate->old[0].threshold == 0);
}
static void
record_allocation(PyThreadState *tstate)
{
struct _gc_thread_state *gc = &((_PyThreadStateImpl *)tstate)->gc;
// We buffer the allocation count to avoid the overhead of atomic
// operations for every allocation.
gc->alloc_count++;
if (gc->alloc_count >= LOCAL_ALLOC_COUNT_THRESHOLD) {
// TODO: Use Py_ssize_t for the generation count.
GCState *gcstate = &tstate->interp->gc;
_Py_atomic_add_int(&gcstate->young.count, (int)gc->alloc_count);
gc->alloc_count = 0;
if (gc_should_collect(gcstate) &&
!_Py_atomic_load_int_relaxed(&gcstate->collecting))
{
_Py_ScheduleGC(tstate);
}
}
}
static void
record_deallocation(PyThreadState *tstate)
{
struct _gc_thread_state *gc = &((_PyThreadStateImpl *)tstate)->gc;
gc->alloc_count--;
if (gc->alloc_count <= -LOCAL_ALLOC_COUNT_THRESHOLD) {
GCState *gcstate = &tstate->interp->gc;
_Py_atomic_add_int(&gcstate->young.count, (int)gc->alloc_count);
gc->alloc_count = 0;
}
}
static void
gc_collect_internal(PyInterpreterState *interp, struct collection_state *state, int generation)
{
_PyEval_StopTheWorld(interp);
// update collection and allocation counters
if (generation+1 < NUM_GENERATIONS) {
state->gcstate->old[generation].count += 1;
}
state->gcstate->young.count = 0;
for (int i = 1; i <= generation; ++i) {
state->gcstate->old[i-1].count = 0;
}
// merge refcounts for all queued objects
merge_all_queued_objects(interp, state);
process_delayed_frees(interp);
// Find unreachable objects
int err = deduce_unreachable_heap(interp, state);
if (err < 0) {
_PyEval_StartTheWorld(interp);
PyErr_NoMemory();
return;
}
// Print debugging information.
if (interp->gc.debug & _PyGC_DEBUG_COLLECTABLE) {
PyObject *op;
WORKSTACK_FOR_EACH(&state->unreachable, op) {
debug_cycle("collectable", op);
}
}
// Record the number of live GC objects
interp->gc.long_lived_total = state->long_lived_total;
// Clear weakrefs and enqueue callbacks (but do not call them).
clear_weakrefs(state);
_PyEval_StartTheWorld(interp);
// Deallocate any object from the refcount merge step
cleanup_worklist(&state->objs_to_decref);
// Call weakref callbacks and finalizers after unpausing other threads to
// avoid potential deadlocks.
call_weakref_callbacks(state);
finalize_garbage(state);
// Handle any objects that may have resurrected after the finalization.
_PyEval_StopTheWorld(interp);
err = handle_resurrected_objects(state);
// Clear free lists in all threads
_PyGC_ClearAllFreeLists(interp);
_PyEval_StartTheWorld(interp);
if (err < 0) {
cleanup_worklist(&state->unreachable);
cleanup_worklist(&state->legacy_finalizers);
cleanup_worklist(&state->wrcb_to_call);
cleanup_worklist(&state->objs_to_decref);
PyErr_NoMemory();
return;
}
// Call tp_clear on objects in the unreachable set. This will cause
// the reference cycles to be broken. It may also cause some objects
// to be freed.
delete_garbage(state);
// Append objects with legacy finalizers to the "gc.garbage" list.
handle_legacy_finalizers(state);
}
/* This is the main function. Read this to understand how the
* collection process works. */
static Py_ssize_t
gc_collect_main(PyThreadState *tstate, int generation, _PyGC_Reason reason)
{
Py_ssize_t m = 0; /* # objects collected */
Py_ssize_t n = 0; /* # unreachable objects that couldn't be collected */
PyTime_t t1 = 0; /* initialize to prevent a compiler warning */
GCState *gcstate = &tstate->interp->gc;
// gc_collect_main() must not be called before _PyGC_Init
// or after _PyGC_Fini()
assert(gcstate->garbage != NULL);
assert(!_PyErr_Occurred(tstate));
int expected = 0;
if (!_Py_atomic_compare_exchange_int(&gcstate->collecting, &expected, 1)) {
// Don't start a garbage collection if one is already in progress.
return 0;
}
if (reason == _Py_GC_REASON_HEAP && !gc_should_collect(gcstate)) {
// Don't collect if the threshold is not exceeded.
_Py_atomic_store_int(&gcstate->collecting, 0);
return 0;
}
assert(generation >= 0 && generation < NUM_GENERATIONS);
#ifdef Py_STATS
if (_Py_stats) {
_Py_stats->object_stats.object_visits = 0;
}
#endif
GC_STAT_ADD(generation, collections, 1);
if (reason != _Py_GC_REASON_SHUTDOWN) {
invoke_gc_callback(tstate, "start", generation, 0, 0);
}
if (gcstate->debug & _PyGC_DEBUG_STATS) {
PySys_WriteStderr("gc: collecting generation %d...\n", generation);
show_stats_each_generations(gcstate);
// ignore error: don't interrupt the GC if reading the clock fails
(void)PyTime_PerfCounterRaw(&t1);
}
if (PyDTrace_GC_START_ENABLED()) {
PyDTrace_GC_START(generation);
}
PyInterpreterState *interp = tstate->interp;
struct collection_state state = {
.interp = interp,
.gcstate = gcstate,
};
gc_collect_internal(interp, &state, generation);
m = state.collected;
n = state.uncollectable;
if (gcstate->debug & _PyGC_DEBUG_STATS) {
PyTime_t t2;
(void)PyTime_PerfCounterRaw(&t2);
double d = PyTime_AsSecondsDouble(t2 - t1);
PySys_WriteStderr(
"gc: done, %zd unreachable, %zd uncollectable, %.4fs elapsed\n",
n+m, n, d);
}
// Clear the current thread's free-list again.
_PyThreadStateImpl *tstate_impl = (_PyThreadStateImpl *)tstate;
_PyObject_ClearFreeLists(&tstate_impl->freelists, 0);
if (_PyErr_Occurred(tstate)) {
if (reason == _Py_GC_REASON_SHUTDOWN) {
_PyErr_Clear(tstate);
}
else {
PyErr_FormatUnraisable("Exception ignored in garbage collection");
}
}
/* Update stats */
struct gc_generation_stats *stats = &gcstate->generation_stats[generation];
stats->collections++;
stats->collected += m;
stats->uncollectable += n;
GC_STAT_ADD(generation, objects_collected, m);
#ifdef Py_STATS
if (_Py_stats) {
GC_STAT_ADD(generation, object_visits,
_Py_stats->object_stats.object_visits);
_Py_stats->object_stats.object_visits = 0;
}
#endif
if (PyDTrace_GC_DONE_ENABLED()) {
PyDTrace_GC_DONE(n + m);
}
if (reason != _Py_GC_REASON_SHUTDOWN) {
invoke_gc_callback(tstate, "stop", generation, m, n);
}
assert(!_PyErr_Occurred(tstate));
_Py_atomic_store_int(&gcstate->collecting, 0);
return n + m;
}
struct get_referrers_args {
struct visitor_args base;
PyObject *objs;
struct worklist results;
};
static int
referrersvisit(PyObject* obj, void *arg)
{
PyObject *objs = arg;
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 bool
visit_get_referrers(const mi_heap_t *heap, const mi_heap_area_t *area,
void *block, size_t block_size, void *args)
{
PyObject *op = op_from_block(block, args, true);
if (op == NULL) {
return true;
}
struct get_referrers_args *arg = (struct get_referrers_args *)args;
if (Py_TYPE(op)->tp_traverse(op, referrersvisit, arg->objs)) {
op->ob_tid = 0; // we will restore the refcount later
worklist_push(&arg->results, op);
}
return true;
}
PyObject *
_PyGC_GetReferrers(PyInterpreterState *interp, PyObject *objs)
{
PyObject *result = PyList_New(0);
if (!result) {
return NULL;
}
_PyEval_StopTheWorld(interp);
// Append all objects to a worklist. This abuses ob_tid. We will restore
// it later. NOTE: We can't append to the PyListObject during
// gc_visit_heaps() because PyList_Append() may reclaim an abandoned
// mimalloc segments while we are traversing them.
struct get_referrers_args args = { .objs = objs };
gc_visit_heaps(interp, &visit_get_referrers, &args.base);
bool error = false;
PyObject *op;
while ((op = worklist_pop(&args.results)) != NULL) {
gc_restore_tid(op);
if (op != objs && PyList_Append(result, op) < 0) {
error = true;
break;
}
}
// In case of error, clear the remaining worklist
while ((op = worklist_pop(&args.results)) != NULL) {
gc_restore_tid(op);
}
_PyEval_StartTheWorld(interp);
if (error) {
Py_DECREF(result);
return NULL;
}
return result;
}
struct get_objects_args {
struct visitor_args base;
struct worklist objects;
};
static bool
visit_get_objects(const mi_heap_t *heap, const mi_heap_area_t *area,
void *block, size_t block_size, void *args)
{
PyObject *op = op_from_block(block, args, true);
if (op == NULL) {
return true;
}
struct get_objects_args *arg = (struct get_objects_args *)args;
op->ob_tid = 0; // we will restore the refcount later
worklist_push(&arg->objects, op);
return true;
}
PyObject *
_PyGC_GetObjects(PyInterpreterState *interp, int generation)
{
PyObject *result = PyList_New(0);
if (!result) {
return NULL;
}
_PyEval_StopTheWorld(interp);
// Append all objects to a worklist. This abuses ob_tid. We will restore
// it later. NOTE: We can't append to the list during gc_visit_heaps()
// because PyList_Append() may reclaim an abandoned mimalloc segment
// while we are traversing it.
struct get_objects_args args = { 0 };
gc_visit_heaps(interp, &visit_get_objects, &args.base);
bool error = false;
PyObject *op;
while ((op = worklist_pop(&args.objects)) != NULL) {
gc_restore_tid(op);
if (op != result && PyList_Append(result, op) < 0) {
error = true;
break;
}
}
// In case of error, clear the remaining worklist
while ((op = worklist_pop(&args.objects)) != NULL) {
gc_restore_tid(op);
}
_PyEval_StartTheWorld(interp);
if (error) {
Py_DECREF(result);
return NULL;
}
return result;
}
static bool
visit_freeze(const mi_heap_t *heap, const mi_heap_area_t *area,
void *block, size_t block_size, void *args)
{
PyObject *op = op_from_block(block, args, true);
if (op != NULL) {
op->ob_gc_bits |= _PyGC_BITS_FROZEN;
}
return true;
}
void
_PyGC_Freeze(PyInterpreterState *interp)
{
struct visitor_args args;
_PyEval_StopTheWorld(interp);
gc_visit_heaps(interp, &visit_freeze, &args);
_PyEval_StartTheWorld(interp);
}
static bool
visit_unfreeze(const mi_heap_t *heap, const mi_heap_area_t *area,
void *block, size_t block_size, void *args)
{
PyObject *op = op_from_block(block, args, true);
if (op != NULL) {
op->ob_gc_bits &= ~_PyGC_BITS_FROZEN;
}
return true;
}
void
_PyGC_Unfreeze(PyInterpreterState *interp)
{
struct visitor_args args;
_PyEval_StopTheWorld(interp);
gc_visit_heaps(interp, &visit_unfreeze, &args);
_PyEval_StartTheWorld(interp);
}
struct count_frozen_args {
struct visitor_args base;
Py_ssize_t count;
};
static bool
visit_count_frozen(const mi_heap_t *heap, const mi_heap_area_t *area,
void *block, size_t block_size, void *args)
{
PyObject *op = op_from_block(block, args, true);
if (op != NULL && (op->ob_gc_bits & _PyGC_BITS_FROZEN) != 0) {
struct count_frozen_args *arg = (struct count_frozen_args *)args;
arg->count++;
}
return true;
}
Py_ssize_t
_PyGC_GetFreezeCount(PyInterpreterState *interp)
{
struct count_frozen_args args = { .count = 0 };
_PyEval_StopTheWorld(interp);
gc_visit_heaps(interp, &visit_count_frozen, &args.base);
_PyEval_StartTheWorld(interp);
return args.count;
}
/* C API for controlling the state of the garbage collector */
int
PyGC_Enable(void)
{
GCState *gcstate = get_gc_state();
int old_state = gcstate->enabled;
gcstate->enabled = 1;
return old_state;
}
int
PyGC_Disable(void)
{
GCState *gcstate = get_gc_state();
int old_state = gcstate->enabled;
gcstate->enabled = 0;
return old_state;
}
int
PyGC_IsEnabled(void)
{
GCState *gcstate = get_gc_state();
return gcstate->enabled;
}
/* Public API to invoke gc.collect() from C */
Py_ssize_t
PyGC_Collect(void)
{
PyThreadState *tstate = _PyThreadState_GET();
GCState *gcstate = &tstate->interp->gc;
if (!gcstate->enabled) {
return 0;
}
Py_ssize_t n;
PyObject *exc = _PyErr_GetRaisedException(tstate);
n = gc_collect_main(tstate, NUM_GENERATIONS - 1, _Py_GC_REASON_MANUAL);
_PyErr_SetRaisedException(tstate, exc);
return n;
}
Py_ssize_t
_PyGC_Collect(PyThreadState *tstate, int generation, _PyGC_Reason reason)
{
return gc_collect_main(tstate, generation, reason);
}
void
_PyGC_CollectNoFail(PyThreadState *tstate)
{
/* 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.
*/
gc_collect_main(tstate, NUM_GENERATIONS - 1, _Py_GC_REASON_SHUTDOWN);
}
void
_PyGC_DumpShutdownStats(PyInterpreterState *interp)
{
GCState *gcstate = &interp->gc;
if (!(gcstate->debug & _PyGC_DEBUG_SAVEALL)
&& gcstate->garbage != NULL && PyList_GET_SIZE(gcstate->garbage) > 0) {
const char *message;
if (gcstate->debug & _PyGC_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(gcstate->garbage)))
{
PyErr_WriteUnraisable(NULL);
}
if (gcstate->debug & _PyGC_DEBUG_UNCOLLECTABLE) {
PyObject *repr = NULL, *bytes = NULL;
repr = PyObject_Repr(gcstate->garbage);
if (!repr || !(bytes = PyUnicode_EncodeFSDefault(repr))) {
PyErr_WriteUnraisable(gcstate->garbage);
}
else {
PySys_WriteStderr(
" %s\n",
PyBytes_AS_STRING(bytes)
);
}
Py_XDECREF(repr);
Py_XDECREF(bytes);
}
}
}
void
_PyGC_Fini(PyInterpreterState *interp)
{
GCState *gcstate = &interp->gc;
Py_CLEAR(gcstate->garbage);
Py_CLEAR(gcstate->callbacks);
/* We expect that none of this interpreters objects are shared
with other interpreters.
See https://github.com/python/cpython/issues/90228. */
}
/* for debugging */
#ifdef Py_DEBUG
static int
visit_validate(PyObject *op, void *parent_raw)
{
PyObject *parent = _PyObject_CAST(parent_raw);
if (_PyObject_IsFreed(op)) {
_PyObject_ASSERT_FAILED_MSG(parent,
"PyObject_GC_Track() object is not valid");
}
return 0;
}
#endif
/* extension modules might be compiled with GC support so these
functions must always be available */
void
PyObject_GC_Track(void *op_raw)
{
PyObject *op = _PyObject_CAST(op_raw);
if (_PyObject_GC_IS_TRACKED(op)) {
_PyObject_ASSERT_FAILED_MSG(op,
"object already tracked "
"by the garbage collector");
}
_PyObject_GC_TRACK(op);
#ifdef Py_DEBUG
/* Check that the object is valid: validate objects traversed
by tp_traverse() */
traverseproc traverse = Py_TYPE(op)->tp_traverse;
(void)traverse(op, visit_validate, op);
#endif
}
void
PyObject_GC_UnTrack(void *op_raw)
{
PyObject *op = _PyObject_CAST(op_raw);
/* Obscure: the Py_TRASHCAN mechanism requires that we be able to
* call PyObject_GC_UnTrack twice on an object.
*/
if (_PyObject_GC_IS_TRACKED(op)) {
_PyObject_GC_UNTRACK(op);
}
}
int
PyObject_IS_GC(PyObject *obj)
{
return _PyObject_IS_GC(obj);
}
void
_Py_ScheduleGC(PyThreadState *tstate)
{
if (!_Py_eval_breaker_bit_is_set(tstate, _PY_GC_SCHEDULED_BIT))
{
_Py_set_eval_breaker_bit(tstate, _PY_GC_SCHEDULED_BIT);
}
}
void
_PyObject_GC_Link(PyObject *op)
{
record_allocation(_PyThreadState_GET());
}
void
_Py_RunGC(PyThreadState *tstate)
{
GCState *gcstate = get_gc_state();
if (!gcstate->enabled) {
return;
}
gc_collect_main(tstate, 0, _Py_GC_REASON_HEAP);
}
static PyObject *
gc_alloc(PyTypeObject *tp, size_t basicsize, size_t presize)
{
PyThreadState *tstate = _PyThreadState_GET();
if (basicsize > PY_SSIZE_T_MAX - presize) {
return _PyErr_NoMemory(tstate);
}
size_t size = presize + basicsize;
char *mem = _PyObject_MallocWithType(tp, size);
if (mem == NULL) {
return _PyErr_NoMemory(tstate);
}
if (presize) {
((PyObject **)mem)[0] = NULL;
((PyObject **)mem)[1] = NULL;
}
PyObject *op = (PyObject *)(mem + presize);
record_allocation(tstate);
return op;
}
PyObject *
_PyObject_GC_New(PyTypeObject *tp)
{
size_t presize = _PyType_PreHeaderSize(tp);
size_t size = _PyObject_SIZE(tp);
if (_PyType_HasFeature(tp, Py_TPFLAGS_INLINE_VALUES)) {
size += _PyInlineValuesSize(tp);
}
PyObject *op = gc_alloc(tp, size, presize);
if (op == NULL) {
return NULL;
}
_PyObject_Init(op, tp);
return op;
}
PyVarObject *
_PyObject_GC_NewVar(PyTypeObject *tp, Py_ssize_t nitems)
{
PyVarObject *op;
if (nitems < 0) {
PyErr_BadInternalCall();
return NULL;
}
size_t presize = _PyType_PreHeaderSize(tp);
size_t size = _PyObject_VAR_SIZE(tp, nitems);
op = (PyVarObject *)gc_alloc(tp, size, presize);
if (op == NULL) {
return NULL;
}
_PyObject_InitVar(op, tp, nitems);
return op;
}
PyObject *
PyUnstable_Object_GC_NewWithExtraData(PyTypeObject *tp, size_t extra_size)
{
size_t presize = _PyType_PreHeaderSize(tp);
PyObject *op = gc_alloc(tp, _PyObject_SIZE(tp) + extra_size, presize);
if (op == NULL) {
return NULL;
}
memset(op, 0, _PyObject_SIZE(tp) + extra_size);
_PyObject_Init(op, tp);
return op;
}
PyVarObject *
_PyObject_GC_Resize(PyVarObject *op, Py_ssize_t nitems)
{
const size_t basicsize = _PyObject_VAR_SIZE(Py_TYPE(op), nitems);
const size_t presize = _PyType_PreHeaderSize(((PyObject *)op)->ob_type);
_PyObject_ASSERT((PyObject *)op, !_PyObject_GC_IS_TRACKED(op));
if (basicsize > (size_t)PY_SSIZE_T_MAX - presize) {
return (PyVarObject *)PyErr_NoMemory();
}
char *mem = (char *)op - presize;
mem = (char *)_PyObject_ReallocWithType(Py_TYPE(op), mem, presize + basicsize);
if (mem == NULL) {
return (PyVarObject *)PyErr_NoMemory();
}
op = (PyVarObject *) (mem + presize);
Py_SET_SIZE(op, nitems);
return op;
}
void
PyObject_GC_Del(void *op)
{
size_t presize = _PyType_PreHeaderSize(((PyObject *)op)->ob_type);
if (_PyObject_GC_IS_TRACKED(op)) {
_PyObject_GC_UNTRACK(op);
#ifdef Py_DEBUG
PyObject *exc = PyErr_GetRaisedException();
if (PyErr_WarnExplicitFormat(PyExc_ResourceWarning, "gc", 0,
"gc", NULL, "Object of type %s is not untracked before destruction",
((PyObject*)op)->ob_type->tp_name)) {
PyErr_WriteUnraisable(NULL);
}
PyErr_SetRaisedException(exc);
#endif
}
record_deallocation(_PyThreadState_GET());
PyObject *self = (PyObject *)op;
if (_PyObject_GC_IS_SHARED_INLINE(self)) {
_PyObject_FreeDelayed(((char *)op)-presize);
}
else {
PyObject_Free(((char *)op)-presize);
}
}
int
PyObject_GC_IsTracked(PyObject* obj)
{
return _PyObject_GC_IS_TRACKED(obj);
}
int
PyObject_GC_IsFinalized(PyObject *obj)
{
return _PyGC_FINALIZED(obj);
}
struct custom_visitor_args {
struct visitor_args base;
gcvisitobjects_t callback;
void *arg;
};
static bool
custom_visitor_wrapper(const mi_heap_t *heap, const mi_heap_area_t *area,
void *block, size_t block_size, void *args)
{
PyObject *op = op_from_block(block, args, false);
if (op == NULL) {
return true;
}
struct custom_visitor_args *wrapper = (struct custom_visitor_args *)args;
if (!wrapper->callback(op, wrapper->arg)) {
return false;
}
return true;
}
// gh-117783: Immortalize objects that use deferred reference counting to
// temporarily work around scaling bottlenecks.
static bool
immortalize_visitor(const mi_heap_t *heap, const mi_heap_area_t *area,
void *block, size_t block_size, void *args)
{
PyObject *op = op_from_block(block, args, false);
if (op != NULL && _PyObject_HasDeferredRefcount(op)) {
_Py_SetImmortal(op);
op->ob_gc_bits &= ~_PyGC_BITS_DEFERRED;
}
return true;
}
void
_PyGC_ImmortalizeDeferredObjects(PyInterpreterState *interp)
{
struct visitor_args args;
_PyEval_StopTheWorld(interp);
if (interp->gc.immortalize == 0) {
gc_visit_heaps(interp, &immortalize_visitor, &args);
interp->gc.immortalize = 1;
}
_PyEval_StartTheWorld(interp);
}
void
PyUnstable_GC_VisitObjects(gcvisitobjects_t callback, void *arg)
{
PyInterpreterState *interp = _PyInterpreterState_GET();
struct custom_visitor_args wrapper = {
.callback = callback,
.arg = arg,
};
_PyEval_StopTheWorld(interp);
gc_visit_heaps(interp, &custom_visitor_wrapper, &wrapper.base);
_PyEval_StartTheWorld(interp);
}
/* 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.
* Free-threading version: Since freelists are managed per thread,
* GC should clear all freelists by traversing all threads.
*/
void
_PyGC_ClearAllFreeLists(PyInterpreterState *interp)
{
HEAD_LOCK(&_PyRuntime);
_PyThreadStateImpl *tstate = (_PyThreadStateImpl *)interp->threads.head;
while (tstate != NULL) {
_PyObject_ClearFreeLists(&tstate->freelists, 0);
tstate = (_PyThreadStateImpl *)tstate->base.next;
}
HEAD_UNLOCK(&_PyRuntime);
}
#endif // Py_GIL_DISABLED
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