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cpython/Python/gc_free_threading.c

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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_dict.h" // _PyInlineValuesSize()
#include "pycore_frame.h" // FRAME_CLEARED
#include "pycore_freelist.h" // _PyObject_ClearFreeLists()
#include "pycore_genobject.h" // _PyGen_GetGeneratorFromFrame()
#include "pycore_initconfig.h" // _PyStatus_NO_MEMORY()
#include "pycore_interp.h" // PyInterpreterState.gc
#include "pycore_interpframe.h" // _PyFrame_GetLocalsArray()
#include "pycore_object_alloc.h" // _PyObject_MallocWithType()
#include "pycore_pystate.h" // _PyThreadState_GET()
#include "pycore_tstate.h" // _PyThreadStateImpl
#include "pycore_tuple.h" // _PyTuple_MaybeUntrack()
#include "pycore_weakref.h" // _PyWeakref_ClearRef()
#include "pydtrace.h"
// Platform-specific includes for get_process_mem_usage().
#ifdef _WIN32
#include <windows.h>
#include <psapi.h> // For GetProcessMemoryInfo
#elif defined(__linux__)
#include <unistd.h> // For sysconf, getpid
#elif defined(__APPLE__)
#include <mach/mach.h>
#include <mach/task.h> // Required for TASK_VM_INFO
#include <unistd.h> // For sysconf, getpid
#elif defined(__FreeBSD__)
#include <sys/types.h>
#include <sys/sysctl.h>
#include <sys/user.h> // Requires sys/user.h for kinfo_proc definition
#include <kvm.h>
#include <unistd.h> // For sysconf, getpid
#include <fcntl.h> // For O_RDONLY
#include <limits.h> // For _POSIX2_LINE_MAX
#elif defined(__OpenBSD__)
#include <sys/types.h>
#include <sys/sysctl.h>
#include <sys/user.h> // For kinfo_proc
#include <unistd.h> // For sysconf, getpid
#endif
// enable the "mark alive" pass of GC
#define GC_ENABLE_MARK_ALIVE 1
// if true, enable the use of "prefetch" CPU instructions
#define GC_ENABLE_PREFETCH_INSTRUCTIONS 1
// include additional roots in "mark alive" pass
#define GC_MARK_ALIVE_EXTRA_ROOTS 1
// include Python stacks as set of known roots
#define GC_MARK_ALIVE_STACKS 1
#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;
_PyGC_Reason reason;
// GH-129236: If we see an active frame without a valid stack pointer,
// we can't collect objects with deferred references because we may not
// see all references.
int skip_deferred_objects;
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_has_bit(PyObject *op, uint8_t bit)
{
return (op->ob_gc_bits & bit) != 0;
}
static inline void
gc_set_bit(PyObject *op, uint8_t bit)
{
op->ob_gc_bits |= bit;
}
static inline void
gc_clear_bit(PyObject *op, uint8_t bit)
{
op->ob_gc_bits &= ~bit;
}
static inline int
gc_is_frozen(PyObject *op)
{
return gc_has_bit(op, _PyGC_BITS_FROZEN);
}
static inline int
gc_is_unreachable(PyObject *op)
{
return gc_has_bit(op, _PyGC_BITS_UNREACHABLE);
}
static inline void
gc_set_unreachable(PyObject *op)
{
gc_set_bit(op, _PyGC_BITS_UNREACHABLE);
}
static inline void
gc_clear_unreachable(PyObject *op)
{
gc_clear_bit(op, _PyGC_BITS_UNREACHABLE);
}
static inline int
gc_is_alive(PyObject *op)
{
return gc_has_bit(op, _PyGC_BITS_ALIVE);
}
#ifdef GC_ENABLE_MARK_ALIVE
static inline void
gc_set_alive(PyObject *op)
{
gc_set_bit(op, _PyGC_BITS_ALIVE);
}
#endif
static inline void
gc_clear_alive(PyObject *op)
{
gc_clear_bit(op, _PyGC_BITS_ALIVE);
}
// 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)) {
assert(!gc_is_alive(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 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
frame_disable_deferred_refcounting(_PyInterpreterFrame *frame)
{
// Convert locals, variables, and the executable object to strong
// references from (possibly) deferred references.
assert(frame->stackpointer != NULL);
assert(frame->owner == FRAME_OWNED_BY_FRAME_OBJECT ||
frame->owner == FRAME_OWNED_BY_GENERATOR);
frame->f_executable = PyStackRef_AsStrongReference(frame->f_executable);
if (frame->owner == FRAME_OWNED_BY_GENERATOR) {
PyGenObject *gen = _PyGen_GetGeneratorFromFrame(frame);
if (gen->gi_frame_state == FRAME_CLEARED) {
// gh-124068: if the generator is cleared, then most fields other
// than f_executable are not valid.
return;
}
}
frame->f_funcobj = PyStackRef_AsStrongReference(frame->f_funcobj);
for (_PyStackRef *ref = frame->localsplus; ref < frame->stackpointer; ref++) {
if (!PyStackRef_IsNullOrInt(*ref) && PyStackRef_IsDeferred(*ref)) {
*ref = PyStackRef_AsStrongReference(*ref);
}
}
}
static void
disable_deferred_refcounting(PyObject *op)
{
if (_PyObject_HasDeferredRefcount(op)) {
op->ob_gc_bits &= ~_PyGC_BITS_DEFERRED;
op->ob_ref_shared -= _Py_REF_SHARED(_Py_REF_DEFERRED, 0);
merge_refcount(op, 0);
// Heap types and code objects also use per-thread refcounting, which
// should also be disabled when we turn off deferred refcounting.
_PyObject_DisablePerThreadRefcounting(op);
}
// Generators and frame objects may contain deferred references to other
// objects. If the pointed-to objects are part of cyclic trash, we may
// have disabled deferred refcounting on them and need to ensure that we
// use strong references, in case the generator or frame object is
// resurrected by a finalizer.
if (PyGen_CheckExact(op) || PyCoro_CheckExact(op) || PyAsyncGen_CheckExact(op)) {
frame_disable_deferred_refcounting(&((PyGenObject *)op)->gi_iframe);
}
else if (PyFrame_Check(op)) {
frame_disable_deferred_refcounting(((PyFrameObject *)op)->f_frame);
}
}
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)) {
assert(!gc_is_alive(op));
gc_restore_tid(op);
gc_clear_unreachable(op);
}
else {
gc_clear_alive(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 && gc_is_frozen(op)) {
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
_Py_FOR_EACH_TSTATE_UNLOCKED(interp, p) {
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 inline void
gc_visit_stackref(_PyStackRef stackref)
{
if (PyStackRef_IsDeferred(stackref) && !PyStackRef_IsNullOrInt(stackref)) {
PyObject *obj = PyStackRef_AsPyObjectBorrow(stackref);
if (_PyObject_GC_IS_TRACKED(obj) && !gc_is_frozen(obj)) {
gc_add_refs(obj, 1);
}
}
}
// Add 1 to the gc_refs for every deferred reference on each thread's stack.
static void
gc_visit_thread_stacks(PyInterpreterState *interp, struct collection_state *state)
{
_Py_FOR_EACH_TSTATE_BEGIN(interp, p) {
_PyCStackRef *c_ref = ((_PyThreadStateImpl *)p)->c_stack_refs;
while (c_ref != NULL) {
gc_visit_stackref(c_ref->ref);
c_ref = c_ref->next;
}
for (_PyInterpreterFrame *f = p->current_frame; f != NULL; f = f->previous) {
if (f->owner >= FRAME_OWNED_BY_INTERPRETER) {
continue;
}
_PyStackRef *top = f->stackpointer;
if (top == NULL) {
// GH-129236: The stackpointer may be NULL in cases where
// the GC is run during a PyStackRef_CLOSE() call. Skip this
// frame and don't collect objects with deferred references.
state->skip_deferred_objects = 1;
continue;
}
gc_visit_stackref(f->f_executable);
while (top != f->localsplus) {
--top;
gc_visit_stackref(*top);
}
}
}
_Py_FOR_EACH_TSTATE_END(interp);
}
// Untrack objects that can never create reference cycles.
// Return true if the object was untracked.
static bool
gc_maybe_untrack(PyObject *op)
{
// Currently we only check for tuples containing only non-GC objects. In
// theory we could check other immutable objects that contain references
// to non-GC objects.
if (PyTuple_CheckExact(op)) {
_PyTuple_MaybeUntrack(op);
if (!_PyObject_GC_IS_TRACKED(op)) {
return true;
}
}
return false;
}
#ifdef GC_ENABLE_MARK_ALIVE
// prefetch buffer and stack //////////////////////////////////
// The buffer is a circular FIFO queue of PyObject pointers. We take
// care to not dereference these pointers until they are taken out of
// the buffer. A prefetch CPU instruction is issued when a pointer is
// put into the buffer. If all is working as expected, there will be
// enough time between the enqueue and dequeue so that the needed memory
// for the object, most importantly ob_gc_bits and ob_type words, will
// already be in the CPU cache.
#define BUFFER_SIZE 256
#define BUFFER_HI 16
#define BUFFER_LO 8
#define BUFFER_MASK (BUFFER_SIZE - 1)
// the buffer size must be an exact power of two
static_assert(BUFFER_SIZE > 0 && !(BUFFER_SIZE & BUFFER_MASK),
"Invalid BUFFER_SIZE, must be power of 2");
// the code below assumes these relationships are true
static_assert(BUFFER_HI < BUFFER_SIZE &&
BUFFER_LO < BUFFER_HI &&
BUFFER_LO > 0,
"Invalid prefetch buffer level settings.");
// Prefetch intructions will fetch the line of data from memory that
// contains the byte specified with the source operand to a location in
// the cache hierarchy specified by a locality hint. The instruction
// is only a hint and the CPU is free to ignore it. Instructions and
// behaviour are CPU specific but the definitions of locality hints
// below are mostly consistent.
//
// * T0 (temporal data) prefetch data into all levels of the cache hierarchy.
//
// * T1 (temporal data with respect to first level cache) prefetch data into
// level 2 cache and higher.
//
// * T2 (temporal data with respect to second level cache) prefetch data into
// level 3 cache and higher, or an implementation-specific choice.
//
// * NTA (non-temporal data with respect to all cache levels) prefetch data into
// non-temporal cache structure and into a location close to the processor,
// minimizing cache pollution.
#if defined(__GNUC__) || defined(__clang__)
#define PREFETCH_T0(ptr) __builtin_prefetch(ptr, 0, 3)
#define PREFETCH_T1(ptr) __builtin_prefetch(ptr, 0, 2)
#define PREFETCH_T2(ptr) __builtin_prefetch(ptr, 0, 1)
#define PREFETCH_NTA(ptr) __builtin_prefetch(ptr, 0, 0)
#elif defined(_MSC_VER) && (defined(_M_X64) || defined(_M_I86)) && !defined(_M_ARM64EC)
#include <mmintrin.h>
#define PREFETCH_T0(ptr) _mm_prefetch((const char*)(ptr), _MM_HINT_T0)
#define PREFETCH_T1(ptr) _mm_prefetch((const char*)(ptr), _MM_HINT_T1)
#define PREFETCH_T2(ptr) _mm_prefetch((const char*)(ptr), _MM_HINT_T2)
#define PREFETCH_NTA(ptr) _mm_prefetch((const char*)(ptr), _MM_HINT_NTA)
#elif defined (__aarch64__)
#define PREFETCH_T0(ptr) \
do { __asm__ __volatile__("prfm pldl1keep, %0" ::"Q"(*(ptr))); } while (0)
#define PREFETCH_T1(ptr) \
do { __asm__ __volatile__("prfm pldl2keep, %0" ::"Q"(*(ptr))); } while (0)
#define PREFETCH_T2(ptr) \
do { __asm__ __volatile__("prfm pldl3keep, %0" ::"Q"(*(ptr))); } while (0)
#define PREFETCH_NTA(ptr) \
do { __asm__ __volatile__("prfm pldl1strm, %0" ::"Q"(*(ptr))); } while (0)
#else
#define PREFETCH_T0(ptr) do { (void)(ptr); } while (0) /* disabled */
#define PREFETCH_T1(ptr) do { (void)(ptr); } while (0) /* disabled */
#define PREFETCH_T2(ptr) do { (void)(ptr); } while (0) /* disabled */
#define PREFETCH_NTA(ptr) do { (void)(ptr); } while (0) /* disabled */
#endif
#ifdef GC_ENABLE_PREFETCH_INSTRUCTIONS
#define prefetch(ptr) PREFETCH_T1(ptr)
#else
#define prefetch(ptr)
#endif
// a contigous sequence of PyObject pointers, can contain NULLs
typedef struct {
PyObject **start;
PyObject **end;
} gc_span_t;
typedef struct {
Py_ssize_t size;
Py_ssize_t capacity;
gc_span_t *stack;
} gc_span_stack_t;
typedef struct {
unsigned int in;
unsigned int out;
_PyObjectStack stack;
gc_span_stack_t spans;
PyObject *buffer[BUFFER_SIZE];
bool use_prefetch;
} gc_mark_args_t;
// Returns number of entries in buffer
static inline unsigned int
gc_mark_buffer_len(gc_mark_args_t *args)
{
return args->in - args->out;
}
// Returns number of free entry slots in buffer
#ifndef NDEBUG
static inline unsigned int
gc_mark_buffer_avail(gc_mark_args_t *args)
{
return BUFFER_SIZE - gc_mark_buffer_len(args);
}
#endif
static inline bool
gc_mark_buffer_is_empty(gc_mark_args_t *args)
{
return args->in == args->out;
}
static inline bool
gc_mark_buffer_is_full(gc_mark_args_t *args)
{
return gc_mark_buffer_len(args) == BUFFER_SIZE;
}
static inline PyObject *
gc_mark_buffer_pop(gc_mark_args_t *args)
{
assert(!gc_mark_buffer_is_empty(args));
PyObject *op = args->buffer[args->out & BUFFER_MASK];
args->out++;
return op;
}
// Called when there is space in the buffer for the object. Issue the
// prefetch instruction and add it to the end of the buffer.
static inline void
gc_mark_buffer_push(PyObject *op, gc_mark_args_t *args)
{
assert(!gc_mark_buffer_is_full(args));
prefetch(op);
args->buffer[args->in & BUFFER_MASK] = op;
args->in++;
}
// Called when we run out of space in the buffer or if the prefetching
// is disabled. The object will be pushed on the gc_mark_args.stack.
static int
gc_mark_stack_push(_PyObjectStack *ms, PyObject *op)
{
if (_PyObjectStack_Push(ms, op) < 0) {
return -1;
}
return 0;
}
static int
gc_mark_span_push(gc_span_stack_t *ss, PyObject **start, PyObject **end)
{
if (start == end) {
return 0;
}
if (ss->size >= ss->capacity) {
if (ss->capacity == 0) {
ss->capacity = 256;
}
else {
ss->capacity *= 2;
}
ss->stack = (gc_span_t *)PyMem_Realloc(ss->stack, ss->capacity * sizeof(gc_span_t));
if (ss->stack == NULL) {
return -1;
}
}
assert(end > start);
ss->stack[ss->size].start = start;
ss->stack[ss->size].end = end;
ss->size++;
return 0;
}
static int
gc_mark_enqueue_no_buffer(PyObject *op, gc_mark_args_t *args)
{
if (op == NULL) {
return 0;
}
if (!gc_has_bit(op, _PyGC_BITS_TRACKED)) {
return 0;
}
if (gc_is_alive(op)) {
return 0; // already visited this object
}
if (gc_maybe_untrack(op)) {
return 0; // was untracked, don't visit it
}
// Need to call tp_traverse on this object. Add to stack and mark it
// alive so we don't traverse it a second time.
gc_set_alive(op);
if (_PyObjectStack_Push(&args->stack, op) < 0) {
return -1;
}
return 0;
}
static inline int
gc_mark_enqueue_no_buffer_visitproc(PyObject *op, void *args)
{
return gc_mark_enqueue_no_buffer(op, (gc_mark_args_t *)args);
}
static int
gc_mark_enqueue_buffer(PyObject *op, gc_mark_args_t *args)
{
assert(op != NULL);
if (!gc_mark_buffer_is_full(args)) {
gc_mark_buffer_push(op, args);
return 0;
}
else {
return gc_mark_stack_push(&args->stack, op);
}
}
static inline int
gc_mark_enqueue_buffer_visitproc(PyObject *op, void *args)
{
return gc_mark_enqueue_buffer(op, (gc_mark_args_t *)args);
}
// Called when we find an object that needs to be marked alive (either from a
// root or from calling tp_traverse).
static int
gc_mark_enqueue(PyObject *op, gc_mark_args_t *args)
{
if (args->use_prefetch) {
return gc_mark_enqueue_buffer(op, args);
}
else {
return gc_mark_enqueue_no_buffer(op, args);
}
}
// Called when we have a contigous sequence of PyObject pointers, either
// a tuple or list object. This will add the items to the buffer if there
// is space for them all otherwise push a new "span" on the span stack. Using
// spans has the advantage of not creating a deep _PyObjectStack stack when
// dealing with long sequences. Those sequences will be processed in smaller
// chunks by the gc_prime_from_spans() function.
static int
gc_mark_enqueue_span(PyObject **item, Py_ssize_t size, gc_mark_args_t *args)
{
Py_ssize_t used = gc_mark_buffer_len(args);
Py_ssize_t free = BUFFER_SIZE - used;
if (free >= size) {
for (Py_ssize_t i = 0; i < size; i++) {
PyObject *op = item[i];
if (op == NULL) {
continue;
}
gc_mark_buffer_push(op, args);
}
}
else {
assert(size > 0);
PyObject **end = &item[size];
if (gc_mark_span_push(&args->spans, item, end) < 0) {
return -1;
}
}
return 0;
}
static bool
gc_clear_alive_bits(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;
}
if (gc_is_alive(op)) {
gc_clear_alive(op);
}
return true;
}
static int
gc_mark_traverse_list(PyObject *self, void *args)
{
PyListObject *list = (PyListObject *)self;
if (list->ob_item == NULL) {
return 0;
}
if (gc_mark_enqueue_span(list->ob_item, PyList_GET_SIZE(list), args) < 0) {
return -1;
}
return 0;
}
static int
gc_mark_traverse_tuple(PyObject *self, void *args)
{
_PyTuple_MaybeUntrack(self);
if (!gc_has_bit(self, _PyGC_BITS_TRACKED)) {
gc_clear_alive(self);
return 0;
}
PyTupleObject *tuple = _PyTuple_CAST(self);
if (gc_mark_enqueue_span(tuple->ob_item, Py_SIZE(tuple), args) < 0) {
return -1;
}
return 0;
}
static void
gc_abort_mark_alive(PyInterpreterState *interp,
struct collection_state *state,
gc_mark_args_t *args)
{
// We failed to allocate memory while doing the "mark alive" phase.
// In that case, free the memory used for marking state and make
// sure that no objects have the alive bit set.
_PyObjectStack_Clear(&args->stack);
if (args->spans.stack != NULL) {
PyMem_Free(args->spans.stack);
}
gc_visit_heaps(interp, &gc_clear_alive_bits, &state->base);
}
#ifdef GC_MARK_ALIVE_STACKS
static int
gc_visit_stackref_mark_alive(gc_mark_args_t *args, _PyStackRef stackref)
{
if (!PyStackRef_IsNullOrInt(stackref)) {
PyObject *op = PyStackRef_AsPyObjectBorrow(stackref);
if (gc_mark_enqueue(op, args) < 0) {
return -1;
}
}
return 0;
}
static int
gc_visit_thread_stacks_mark_alive(PyInterpreterState *interp, gc_mark_args_t *args)
{
int err = 0;
_Py_FOR_EACH_TSTATE_BEGIN(interp, p) {
for (_PyInterpreterFrame *f = p->current_frame; f != NULL; f = f->previous) {
if (f->owner >= FRAME_OWNED_BY_INTERPRETER) {
continue;
}
if (f->stackpointer == NULL) {
// GH-129236: The stackpointer may be NULL in cases where
// the GC is run during a PyStackRef_CLOSE() call. Skip this
// frame for now.
continue;
}
_PyStackRef *top = f->stackpointer;
if (gc_visit_stackref_mark_alive(args, f->f_executable) < 0) {
err = -1;
goto exit;
}
while (top != f->localsplus) {
--top;
if (gc_visit_stackref_mark_alive(args, *top) < 0) {
err = -1;
goto exit;
}
}
}
}
exit:
_Py_FOR_EACH_TSTATE_END(interp);
return err;
}
#endif // GC_MARK_ALIVE_STACKS
#endif // GC_ENABLE_MARK_ALIVE
static void
queue_untracked_obj_decref(PyObject *op, struct collection_state *state)
{
if (!_PyObject_GC_IS_TRACKED(op)) {
// 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_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 (refcount == 0) {
queue_untracked_obj_decref(op, state);
}
}
}
static void
queue_freed_object(PyObject *obj, void *arg)
{
queue_untracked_obj_decref(obj, arg);
}
static void
process_delayed_frees(PyInterpreterState *interp, struct collection_state *state)
{
// While we are in a "stop the world" pause, 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);
// Merge the queues from other threads into our own queue so that we can
// process all of the pending delayed free requests at once.
_Py_FOR_EACH_TSTATE_BEGIN(interp, p) {
_PyThreadStateImpl *other = (_PyThreadStateImpl *)p;
if (other != current_tstate) {
llist_concat(&current_tstate->mem_free_queue, &other->mem_free_queue);
}
}
_Py_FOR_EACH_TSTATE_END(interp);
_PyMem_ProcessDelayedNoDealloc((PyThreadState *)current_tstate, queue_freed_object, state);
}
// 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)
&& !gc_is_frozen(op)
&& !gc_is_alive(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;
}
if (gc_is_alive(op)) {
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);
if (_PyObject_HasDeferredRefcount(op)) {
refcount -= _Py_REF_DEFERRED;
}
_PyObject_ASSERT(op, refcount >= 0);
if (refcount > 0 && !_PyObject_HasDeferredRefcount(op)) {
if (gc_maybe_untrack(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, void *stack)
{
if (gc_is_unreachable(op)) {
_PyObject_ASSERT(op, _PyObject_GC_IS_TRACKED(op));
gc_clear_unreachable(op);
return _PyObjectStack_Push((_PyObjectStack *)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, 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_alive_bits(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_alive(op),
"object should not be marked as alive yet");
return true;
}
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;
}
if (gc_is_alive(op)) {
_PyObject_ASSERT(op, !gc_is_unreachable(op));
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;
}
if (gc_is_alive(op) || !gc_is_unreachable(op)) {
// Object was already marked as reachable.
return true;
}
_PyObject_ASSERT_WITH_MSG(op, gc_get_refs(op) >= 0,
"refcount is too small");
// GH-129236: If we've seen an active frame without a valid stack pointer,
// then we can't collect objects with deferred references because we may
// have missed some reference to the object on the stack. In that case,
// treat the object as reachable even if gc_refs is zero.
struct collection_state *state = (struct collection_state *)args;
int keep_alive = (state->skip_deferred_objects &&
_PyObject_HasDeferredRefcount(op));
if (gc_get_refs(op) != 0 || keep_alive) {
// 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);
gc_clear_alive(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);
}
return true;
}
if (state->reason == _Py_GC_REASON_SHUTDOWN) {
// Disable deferred refcounting for reachable objects as well during
// interpreter shutdown. This ensures that these objects are collected
// immediately when their last reference is removed.
disable_deferred_refcounting(op);
}
// object is reachable, restore `ob_tid`; we're done with these objects
gc_restore_tid(op);
gc_clear_alive(op);
state->long_lived_total++;
return true;
}
static int
move_legacy_finalizer_reachable(struct collection_state *state);
#ifdef GC_ENABLE_MARK_ALIVE
static void
gc_prime_from_spans(gc_mark_args_t *args)
{
unsigned int space = BUFFER_HI - gc_mark_buffer_len(args);
// there should always be at least this amount of space
assert(space <= gc_mark_buffer_avail(args));
assert(space <= BUFFER_HI);
gc_span_t entry = args->spans.stack[--args->spans.size];
// spans on the stack should always have one or more elements
assert(entry.start < entry.end);
do {
PyObject *op = *entry.start;
entry.start++;
if (op != NULL) {
gc_mark_buffer_push(op, args);
space--;
if (space == 0) {
// buffer is as full as we want and not done with span
gc_mark_span_push(&args->spans, entry.start, entry.end);
return;
}
}
} while (entry.start < entry.end);
}
static void
gc_prime_buffer(gc_mark_args_t *args)
{
if (args->spans.size > 0) {
gc_prime_from_spans(args);
}
else {
// When priming, don't fill the buffer too full since that would
// likely cause the stack to be used shortly after when it
// fills. We want to use the buffer as much as possible and so
// we only fill to BUFFER_HI, not BUFFER_SIZE.
Py_ssize_t space = BUFFER_HI - gc_mark_buffer_len(args);
assert(space > 0);
do {
PyObject *op = _PyObjectStack_Pop(&args->stack);
if (op == NULL) {
return;
}
gc_mark_buffer_push(op, args);
space--;
} while (space > 0);
}
}
static int
gc_propagate_alive_prefetch(gc_mark_args_t *args)
{
for (;;) {
Py_ssize_t buf_used = gc_mark_buffer_len(args);
if (buf_used <= BUFFER_LO) {
// The mark buffer is getting empty. If it's too empty
// then there will not be enough delay between issuing
// the prefetch and when the object is actually accessed.
// Prime the buffer with object pointers from the stack or
// from the spans, if there are any available.
gc_prime_buffer(args);
if (gc_mark_buffer_is_empty(args)) {
return 0;
}
}
PyObject *op = gc_mark_buffer_pop(args);
if (!gc_has_bit(op, _PyGC_BITS_TRACKED)) {
continue;
}
if (gc_is_alive(op)) {
continue; // already visited this object
}
// Need to call tp_traverse on this object. Mark it alive so we
// don't traverse it a second time.
gc_set_alive(op);
traverseproc traverse = Py_TYPE(op)->tp_traverse;
if (traverse == PyList_Type.tp_traverse) {
if (gc_mark_traverse_list(op, args) < 0) {
return -1;
}
}
else if (traverse == PyTuple_Type.tp_traverse) {
if (gc_mark_traverse_tuple(op, args) < 0) {
return -1;
}
}
else if (traverse(op, gc_mark_enqueue_buffer_visitproc, args) < 0) {
return -1;
}
}
}
static int
gc_propagate_alive(gc_mark_args_t *args)
{
if (args->use_prefetch) {
return gc_propagate_alive_prefetch(args);
}
else {
for (;;) {
PyObject *op = _PyObjectStack_Pop(&args->stack);
if (op == NULL) {
break;
}
assert(_PyObject_GC_IS_TRACKED(op));
assert(gc_is_alive(op));
traverseproc traverse = Py_TYPE(op)->tp_traverse;
if (traverse(op, gc_mark_enqueue_no_buffer_visitproc, args) < 0) {
return -1;
}
}
return 0;
}
}
// Using tp_traverse, mark everything reachable from known root objects
// (which must be non-garbage) as alive (_PyGC_BITS_ALIVE is set). In
// most programs, this marks nearly all objects that are not actually
// unreachable.
//
// Actually alive objects can be missed in this pass if they are alive
// due to being referenced from an unknown root (e.g. an extension
// module global), some tp_traverse methods are either missing or not
// accurate, or objects that have been untracked. Objects that are only
// reachable from the aforementioned are also missed.
//
// If gc.freeze() is used, this pass is disabled since it is unlikely to
// help much. The next stages of cyclic GC will ignore objects with the
// alive bit set.
//
// Returns -1 on failure (out of memory).
static int
gc_mark_alive_from_roots(PyInterpreterState *interp,
struct collection_state *state)
{
#ifdef GC_DEBUG
// Check that all objects don't have alive bit set
gc_visit_heaps(interp, &validate_alive_bits, &state->base);
#endif
gc_mark_args_t mark_args = { 0 };
// Using prefetch instructions is only a win if the set of objects being
// examined by the GC does not fit into CPU caches. Otherwise, using the
// buffer and prefetch instructions is just overhead. Using the long lived
// object count seems a good estimate of if things will fit in the cache.
// On 64-bit platforms, the minimum object size is 32 bytes. A 4MB L2 cache
// would hold about 130k objects.
mark_args.use_prefetch = interp->gc.long_lived_total > 200000;
#define MARK_ENQUEUE(op) \
if (op != NULL ) { \
if (gc_mark_enqueue(op, &mark_args) < 0) { \
gc_abort_mark_alive(interp, state, &mark_args); \
return -1; \
} \
}
MARK_ENQUEUE(interp->sysdict);
#ifdef GC_MARK_ALIVE_EXTRA_ROOTS
MARK_ENQUEUE(interp->builtins);
MARK_ENQUEUE(interp->dict);
struct types_state *types = &interp->types;
for (int i = 0; i < _Py_MAX_MANAGED_STATIC_BUILTIN_TYPES; i++) {
MARK_ENQUEUE(types->builtins.initialized[i].tp_dict);
MARK_ENQUEUE(types->builtins.initialized[i].tp_subclasses);
}
for (int i = 0; i < _Py_MAX_MANAGED_STATIC_EXT_TYPES; i++) {
MARK_ENQUEUE(types->for_extensions.initialized[i].tp_dict);
MARK_ENQUEUE(types->for_extensions.initialized[i].tp_subclasses);
}
#endif
#ifdef GC_MARK_ALIVE_STACKS
if (gc_visit_thread_stacks_mark_alive(interp, &mark_args) < 0) {
gc_abort_mark_alive(interp, state, &mark_args);
return -1;
}
#endif
#undef MARK_ENQUEUE
// Use tp_traverse to find everything reachable from roots.
if (gc_propagate_alive(&mark_args) < 0) {
gc_abort_mark_alive(interp, state, &mark_args);
return -1;
}
assert(mark_args.spans.size == 0);
if (mark_args.spans.stack != NULL) {
PyMem_Free(mark_args.spans.stack);
}
assert(mark_args.stack.head == NULL);
return 0;
}
#endif // GC_ENABLE_MARK_ALIVE
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
// Visit the thread stacks to account for any deferred references.
gc_visit_thread_stacks(interp, state);
// 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_FormatUnraisable("Exception ignored while "
"calling weakref callback %R", 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;
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;
}
int
_PyGC_VisitStackRef(_PyStackRef *ref, visitproc visit, void *arg)
{
// This is a bit tricky! We want to ignore deferred references when
// computing the incoming references, but otherwise treat them like
// regular references.
assert(!PyStackRef_IsTaggedInt(*ref));
if (!PyStackRef_IsDeferred(*ref) ||
(visit != visit_decref && visit != visit_decref_unreachable))
{
Py_VISIT(PyStackRef_AsPyObjectBorrow(*ref));
}
return 0;
}
int
_PyGC_VisitFrameStack(_PyInterpreterFrame *frame, visitproc visit, void *arg)
{
_PyStackRef *ref = _PyFrame_GetLocalsArray(frame);
/* locals and stack */
for (; ref < frame->stackpointer; ref++) {
_Py_VISIT_STACKREF(*ref);
}
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, 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 while "
"invoking gc callbacks");
return;
}
}
PyObject *phase_obj = PyUnicode_FromString(phase);
if (phase_obj == NULL) {
Py_XDECREF(info);
PyErr_FormatUnraisable("Exception ignored while "
"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_FormatUnraisable("Exception ignored while "
"calling GC callback %R", 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);
}
}
// Return the memory usage (typically RSS + swap) of the process, in units of
// KB. Returns -1 if this operation is not supported or on failure.
static Py_ssize_t
get_process_mem_usage(void)
{
#ifdef _WIN32
// Windows implementation using GetProcessMemoryInfo
// Returns WorkingSetSize + PagefileUsage
PROCESS_MEMORY_COUNTERS pmc;
HANDLE hProcess = GetCurrentProcess();
if (NULL == hProcess) {
// Should not happen for the current process
return -1;
}
// GetProcessMemoryInfo returns non-zero on success
if (GetProcessMemoryInfo(hProcess, &pmc, sizeof(pmc))) {
// Values are in bytes, convert to KB.
return (Py_ssize_t)((pmc.WorkingSetSize + pmc.PagefileUsage) / 1024);
}
else {
return -1;
}
#elif __linux__
FILE* fp = fopen("/proc/self/status", "r");
if (fp == NULL) {
return -1;
}
char line_buffer[256];
long long rss_kb = -1;
long long swap_kb = -1;
while (fgets(line_buffer, sizeof(line_buffer), fp) != NULL) {
if (rss_kb == -1 && strncmp(line_buffer, "VmRSS:", 6) == 0) {
sscanf(line_buffer + 6, "%lld", &rss_kb);
}
else if (swap_kb == -1 && strncmp(line_buffer, "VmSwap:", 7) == 0) {
sscanf(line_buffer + 7, "%lld", &swap_kb);
}
if (rss_kb != -1 && swap_kb != -1) {
break; // Found both
}
}
fclose(fp);
if (rss_kb != -1 && swap_kb != -1) {
return (Py_ssize_t)(rss_kb + swap_kb);
}
return -1;
#elif defined(__APPLE__)
// --- MacOS (Darwin) ---
// Returns phys_footprint (RAM + compressed memory)
task_vm_info_data_t vm_info;
mach_msg_type_number_t count = TASK_VM_INFO_COUNT;
kern_return_t kerr;
kerr = task_info(mach_task_self(), TASK_VM_INFO, (task_info_t)&vm_info, &count);
if (kerr != KERN_SUCCESS) {
return -1;
}
// phys_footprint is in bytes. Convert to KB.
return (Py_ssize_t)(vm_info.phys_footprint / 1024);
#elif defined(__FreeBSD__)
// NOTE: Returns RSS only. Per-process swap usage isn't readily available
long page_size_kb = sysconf(_SC_PAGESIZE) / 1024;
if (page_size_kb <= 0) {
return -1;
}
// Using /dev/null for vmcore avoids needing dump file.
// NULL for kernel file uses running kernel.
char errbuf[_POSIX2_LINE_MAX]; // For kvm error messages
kvm_t *kd = kvm_openfiles(NULL, "/dev/null", NULL, O_RDONLY, errbuf);
if (kd == NULL) {
return -1;
}
// KERN_PROC_PID filters for the specific process ID
// n_procs will contain the number of processes returned (should be 1 or 0)
pid_t pid = getpid();
int n_procs;
struct kinfo_proc *kp = kvm_getprocs(kd, KERN_PROC_PID, pid, &n_procs);
if (kp == NULL) {
kvm_close(kd);
return -1;
}
Py_ssize_t rss_kb = -1;
if (n_procs > 0) {
// kp[0] contains the info for our process
// ki_rssize is in pages. Convert to KB.
rss_kb = (Py_ssize_t)kp->ki_rssize * page_size_kb;
}
else {
// Process with PID not found, shouldn't happen for self.
rss_kb = -1;
}
kvm_close(kd);
return rss_kb;
#elif defined(__OpenBSD__)
// NOTE: Returns RSS only. Per-process swap usage isn't readily available
long page_size_kb = sysconf(_SC_PAGESIZE) / 1024;
if (page_size_kb <= 0) {
return -1;
}
struct kinfo_proc kp;
pid_t pid = getpid();
int mib[6];
size_t len = sizeof(kp);
mib[0] = CTL_KERN;
mib[1] = KERN_PROC;
mib[2] = KERN_PROC_PID;
mib[3] = pid;
mib[4] = sizeof(struct kinfo_proc); // size of the structure we want
mib[5] = 1; // want 1 structure back
if (sysctl(mib, 6, &kp, &len, NULL, 0) == -1) {
return -1;
}
if (len > 0) {
// p_vm_rssize is in pages on OpenBSD. Convert to KB.
return (Py_ssize_t)kp.p_vm_rssize * page_size_kb;
}
else {
// Process info not returned
return -1;
}
#else
// Unsupported platform
return -1;
#endif
}
static bool
gc_should_collect_mem_usage(GCState *gcstate)
{
Py_ssize_t mem = get_process_mem_usage();
if (mem < 0) {
// Reading process memory usage is not support or failed.
return true;
}
int threshold = gcstate->young.threshold;
Py_ssize_t deferred = _Py_atomic_load_ssize_relaxed(&gcstate->deferred_count);
if (deferred > threshold * 40) {
// Too many new container objects since last GC, even though memory use
// might not have increased much. This is intended to avoid resource
// exhaustion if some objects consume resources but don't result in a
// memory usage increase. We use 40x as the factor here because older
// versions of Python would do full collections after roughly every
// 70,000 new container objects.
return true;
}
Py_ssize_t last_mem = _Py_atomic_load_ssize_relaxed(&gcstate->last_mem);
Py_ssize_t mem_threshold = Py_MAX(last_mem / 10, 128);
if ((mem - last_mem) > mem_threshold) {
// The process memory usage has increased too much, do a collection.
return true;
}
else {
// The memory usage has not increased enough, defer the collection and
// clear the young object count so we don't check memory usage again
// on the next call to gc_should_collect().
PyMutex_Lock(&gcstate->mutex);
int young_count = _Py_atomic_exchange_int(&gcstate->young.count, 0);
_Py_atomic_store_ssize_relaxed(&gcstate->deferred_count,
gcstate->deferred_count + young_count);
PyMutex_Unlock(&gcstate->mutex);
return false;
}
}
static bool
gc_should_collect(GCState *gcstate)
{
int count = _Py_atomic_load_int_relaxed(&gcstate->young.count);
int threshold = gcstate->young.threshold;
int gc_enabled = _Py_atomic_load_int_relaxed(&gcstate->enabled);
if (count <= threshold || threshold == 0 || !gc_enabled) {
return false;
}
if (gcstate->old[0].threshold == 0) {
// A few tests rely on immediate scheduling of the GC so we ignore the
// extra conditions if generations[1].threshold is set to zero.
return true;
}
if (count < gcstate->long_lived_total / 4) {
// Avoid quadratic behavior by scaling threshold to the number of live
// objects.
return false;
}
return gc_should_collect_mem_usage(gcstate);
}
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;
state->gcstate->deferred_count = 0;
for (int i = 1; i <= generation; ++i) {
state->gcstate->old[i-1].count = 0;
}
_Py_FOR_EACH_TSTATE_BEGIN(interp, p) {
_PyThreadStateImpl *tstate = (_PyThreadStateImpl *)p;
// merge per-thread refcount for types into the type's actual refcount
_PyObject_MergePerThreadRefcounts(tstate);
// merge refcounts for all queued objects
merge_queued_objects(tstate, state);
}
_Py_FOR_EACH_TSTATE_END(interp);
process_delayed_frees(interp, state);
#ifdef GC_ENABLE_MARK_ALIVE
// If gc.freeze() was used, it seems likely that doing this "mark alive"
// pass will not be a performance win. Typically the majority of alive
// objects will be marked as frozen and will be skipped anyhow, without
// doing this extra work. Doing this pass also defeats one of the
// purposes of using freeze: avoiding writes to objects that are frozen.
// So, we just skip this if gc.freeze() was used.
if (!state->gcstate->freeze_active) {
// Mark objects reachable from known roots as "alive". These will
// be ignored for rest of the GC pass.
int err = gc_mark_alive_from_roots(interp, state);
if (err < 0) {
_PyEval_StartTheWorld(interp);
PyErr_NoMemory();
return;
}
}
#endif
// Find unreachable objects
int err = deduce_unreachable_heap(interp, state);
if (err < 0) {
_PyEval_StartTheWorld(interp);
PyErr_NoMemory();
return;
}
#ifdef GC_DEBUG
// At this point, no object should have the alive bit set
gc_visit_heaps(interp, &validate_alive_bits, &state->base);
#endif
// 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);
// Store the current memory usage, can be smaller now if breaking cycles
// freed some memory.
Py_ssize_t last_mem = get_process_mem_usage();
_Py_atomic_store_ssize_relaxed(&state->gcstate->last_mem, last_mem);
// 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,
.reason = reason,
};
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;
}
static PyObject *
list_from_object_stack(_PyObjectStack *stack)
{
PyObject *list = PyList_New(_PyObjectStack_Size(stack));
if (list == NULL) {
PyObject *op;
while ((op = _PyObjectStack_Pop(stack)) != NULL) {
Py_DECREF(op);
}
return NULL;
}
PyObject *op;
Py_ssize_t idx = 0;
while ((op = _PyObjectStack_Pop(stack)) != NULL) {
assert(idx < PyList_GET_SIZE(list));
PyList_SET_ITEM(list, idx++, op);
}
assert(idx == PyList_GET_SIZE(list));
return list;
}
struct get_referrers_args {
struct visitor_args base;
PyObject *objs;
_PyObjectStack 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;
}
if (op->ob_gc_bits & (_PyGC_BITS_UNREACHABLE | _PyGC_BITS_FROZEN)) {
// Exclude unreachable objects (in-progress GC) and frozen
// objects from gc.get_objects() to match the default build.
return true;
}
struct get_referrers_args *arg = (struct get_referrers_args *)args;
if (op == arg->objs) {
// Don't include the tuple itself in the referrers list.
return true;
}
if (Py_TYPE(op)->tp_traverse(op, referrersvisit, arg->objs)) {
if (_PyObjectStack_Push(&arg->results, Py_NewRef(op)) < 0) {
return false;
}
}
return true;
}
PyObject *
_PyGC_GetReferrers(PyInterpreterState *interp, PyObject *objs)
{
// 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 };
_PyEval_StopTheWorld(interp);
int err = gc_visit_heaps(interp, &visit_get_referrers, &args.base);
_PyEval_StartTheWorld(interp);
PyObject *list = list_from_object_stack(&args.results);
if (err < 0) {
PyErr_NoMemory();
Py_CLEAR(list);
}
return list;
}
struct get_objects_args {
struct visitor_args base;
_PyObjectStack 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;
}
if (op->ob_gc_bits & (_PyGC_BITS_UNREACHABLE | _PyGC_BITS_FROZEN)) {
// Exclude unreachable objects (in-progress GC) and frozen
// objects from gc.get_objects() to match the default build.
return true;
}
struct get_objects_args *arg = (struct get_objects_args *)args;
if (_PyObjectStack_Push(&arg->objects, Py_NewRef(op)) < 0) {
return false;
}
return true;
}
PyObject *
_PyGC_GetObjects(PyInterpreterState *interp, int generation)
{
// 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_objects_args args = { 0 };
_PyEval_StopTheWorld(interp);
int err = gc_visit_heaps(interp, &visit_get_objects, &args.base);
_PyEval_StartTheWorld(interp);
PyObject *list = list_from_object_stack(&args.objects);
if (err < 0) {
PyErr_NoMemory();
Py_CLEAR(list);
}
return list;
}
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 && !gc_is_unreachable(op)) {
op->ob_gc_bits |= _PyGC_BITS_FROZEN;
}
return true;
}
void
_PyGC_Freeze(PyInterpreterState *interp)
{
struct visitor_args args;
_PyEval_StopTheWorld(interp);
GCState *gcstate = get_gc_state();
gcstate->freeze_active = true;
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) {
gc_clear_bit(op, _PyGC_BITS_FROZEN);
}
return true;
}
void
_PyGC_Unfreeze(PyInterpreterState *interp)
{
struct visitor_args args;
_PyEval_StopTheWorld(interp);
GCState *gcstate = get_gc_state();
gcstate->freeze_active = false;
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 && gc_is_frozen(op)) {
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();
return _Py_atomic_exchange_int(&gcstate->enabled, 1);
}
int
PyGC_Disable(void)
{
GCState *gcstate = get_gc_state();
return _Py_atomic_exchange_int(&gcstate->enabled, 0);
}
int
PyGC_IsEnabled(void)
{
GCState *gcstate = get_gc_state();
return _Py_atomic_load_int_relaxed(&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 (!_Py_atomic_load_int_relaxed(&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_FormatUnraisable("Exception ignored in GC shutdown");
}
if (gcstate->debug & _PyGC_DEBUG_UNCOLLECTABLE) {
PyObject *repr = NULL, *bytes = NULL;
repr = PyObject_Repr(gcstate->garbage);
if (!repr || !(bytes = PyUnicode_EncodeFSDefault(repr))) {
PyErr_FormatUnraisable("Exception ignored in GC shutdown "
"while formatting 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);
/* The code for some objects, such as tuples, is a bit
* sloppy about when the object is tracked and untracked. */
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)
{
if (!PyGC_IsEnabled()) {
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);
if (tp->tp_flags & Py_TPFLAGS_INLINE_VALUES) {
_PyObject_InitInlineValues(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);
size_t size = _PyObject_SIZE(tp) + extra_size;
PyObject *op = gc_alloc(tp, size, presize);
if (op == NULL) {
return NULL;
}
memset((char *)op + sizeof(PyObject), 0, size - sizeof(PyObject));
_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",
Py_TYPE(op)->tp_name))
{
PyErr_FormatUnraisable("Exception ignored on object deallocation");
}
PyErr_SetRaisedException(exc);
#endif
}
record_deallocation(_PyThreadState_GET());
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;
}
void
_PyGC_VisitObjectsWorldStopped(PyInterpreterState *interp,
gcvisitobjects_t callback, void *arg)
{
struct custom_visitor_args wrapper = {
.callback = callback,
.arg = arg,
};
gc_visit_heaps(interp, &custom_visitor_wrapper, &wrapper.base);
}
void
PyUnstable_GC_VisitObjects(gcvisitobjects_t callback, void *arg)
{
PyInterpreterState *interp = _PyInterpreterState_GET();
_PyEval_StopTheWorld(interp);
_PyGC_VisitObjectsWorldStopped(interp, callback, arg);
_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)
{
_Py_FOR_EACH_TSTATE_BEGIN(interp, p) {
_PyThreadStateImpl *tstate = (_PyThreadStateImpl *)p;
_PyObject_ClearFreeLists(&tstate->freelists, 0);
}
_Py_FOR_EACH_TSTATE_END(interp);
}
#endif // Py_GIL_DISABLED
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