Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

gh-129236: Use stackpointer in free threaded GC #129240

Merged
merged 5 commits into from
Jan 29, 2025
Merged

gh-129236: Use stackpointer in free threaded GC #129240

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
5 commits
Select commit Hold shift + click to select a range
1ec055b
gh-129236: Use `stackpointer` in free threaded GC
colesbury Jan 23, 2025
fcaee80
Remove additional frame initialization
colesbury Jan 24, 2025
ca32c7b
Update Python/gc_free_threading.c
colesbury Jan 24, 2025
1c8a2e3
Update comment
colesbury Jan 24, 2025
57a34c2
Update comment and logic in mark_heap_visitor
colesbury Jan 24, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
24 changes: 0 additions & 24 deletions Include/internal/pycore_frame.h
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -159,13 +159,6 @@ static inline void _PyFrame_Copy(_PyInterpreterFrame *src, _PyInterpreterFrame *
// Don't leave a dangling pointer to the old frame when creating generators
// and coroutines:
dest->previous = NULL;

#ifdef Py_GIL_DISABLED
PyCodeObject *co = _PyFrame_GetCode(dest);
for (int i = stacktop; i < co->co_nlocalsplus + co->co_stacksize; i++) {
dest->localsplus[i] = PyStackRef_NULL;
}
#endif
}

#ifdef Py_GIL_DISABLED
Expand Down Expand Up @@ -219,16 +212,6 @@ _PyFrame_Initialize(
for (int i = null_locals_from; i < code->co_nlocalsplus; i++) {
frame->localsplus[i] = PyStackRef_NULL;
}

#ifdef Py_GIL_DISABLED
// On GIL disabled, we walk the entire stack in GC. Since stacktop
// is not always in sync with the real stack pointer, we have
// no choice but to traverse the entire stack.
// This just makes sure we don't pass the GC invalid stack values.
for (int i = code->co_nlocalsplus; i < code->co_nlocalsplus + code->co_stacksize; i++) {
frame->localsplus[i] = PyStackRef_NULL;
}
#endif
}

/* Gets the pointer to the locals array
Expand Down Expand Up @@ -399,13 +382,6 @@ _PyFrame_PushTrampolineUnchecked(PyThreadState *tstate, PyCodeObject *code, int
frame->owner = FRAME_OWNED_BY_THREAD;
frame->visited = 0;
frame->return_offset = 0;

#ifdef Py_GIL_DISABLED
assert(code->co_nlocalsplus == 0);
for (int i = 0; i < code->co_stacksize; i++) {
frame->localsplus[i] = PyStackRef_NULL;
}
#endif
return frame;
}

Expand Down
80 changes: 52 additions & 28 deletions Python/gc_free_threading.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -67,6 +67,10 @@ struct collection_state {
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;
Expand Down Expand Up @@ -413,9 +417,6 @@ gc_visit_heaps(PyInterpreterState *interp, mi_block_visit_fun *visitor,
static inline void
gc_visit_stackref(_PyStackRef stackref)
{
// Note: we MUST check that it is deferred before checking the rest.
// Otherwise we might read into invalid memory due to non-deferred references
// being dead already.
if (PyStackRef_IsDeferred(stackref) && !PyStackRef_IsNull(stackref)) {
PyObject *obj = PyStackRef_AsPyObjectBorrow(stackref);
if (_PyObject_GC_IS_TRACKED(obj) && !gc_is_frozen(obj)) {
Expand All @@ -426,20 +427,27 @@ gc_visit_stackref(_PyStackRef stackref)

// Add 1 to the gc_refs for every deferred reference on each thread's stack.
static void
gc_visit_thread_stacks(PyInterpreterState *interp)
gc_visit_thread_stacks(PyInterpreterState *interp, struct collection_state *state)
{
_Py_FOR_EACH_TSTATE_BEGIN(interp, p) {
for (_PyInterpreterFrame *f = p->current_frame; f != NULL; f = f->previous) {
PyObject *executable = PyStackRef_AsPyObjectBorrow(f->f_executable);
if (executable == NULL || !PyCode_Check(executable)) {
if (f->owner >= FRAME_OWNED_BY_INTERPRETER) {
Copy link
Contributor Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I also updated this to match the condition in Python/gc.c.

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;
}

PyCodeObject *co = (PyCodeObject *)executable;
int max_stack = co->co_nlocalsplus + co->co_stacksize;
gc_visit_stackref(f->f_executable);
for (int i = 0; i < max_stack; i++) {
gc_visit_stackref(f->localsplus[i]);
while (top != f->localsplus) {
--top;
gc_visit_stackref(*top);
}
}
}
Expand Down Expand Up @@ -519,10 +527,7 @@ gc_abort_mark_alive(PyInterpreterState *interp,
static int
gc_visit_stackref_mark_alive(_PyObjectStack *stack, _PyStackRef stackref)
{
// Note: we MUST check that it is deferred before checking the rest.
// Otherwise we might read into invalid memory due to non-deferred references
// being dead already.
if (PyStackRef_IsDeferred(stackref) && !PyStackRef_IsNull(stackref)) {
if (!PyStackRef_IsNull(stackref)) {
PyObject *op = PyStackRef_AsPyObjectBorrow(stackref);
if (mark_alive_stack_push(op, stack) < 0) {
return -1;
Expand All @@ -534,27 +539,37 @@ gc_visit_stackref_mark_alive(_PyObjectStack *stack, _PyStackRef stackref)
static int
gc_visit_thread_stacks_mark_alive(PyInterpreterState *interp, _PyObjectStack *stack)
{
int err = 0;
_Py_FOR_EACH_TSTATE_BEGIN(interp, p) {
for (_PyInterpreterFrame *f = p->current_frame; f != NULL; f = f->previous) {
PyObject *executable = PyStackRef_AsPyObjectBorrow(f->f_executable);
if (executable == NULL || !PyCode_Check(executable)) {
if (f->owner >= FRAME_OWNED_BY_INTERPRETER) {
continue;
}

PyCodeObject *co = (PyCodeObject *)executable;
int max_stack = co->co_nlocalsplus + co->co_stacksize;
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(stack, f->f_executable) < 0) {
return -1;
err = -1;
goto exit;
}
for (int i = 0; i < max_stack; i++) {
if (gc_visit_stackref_mark_alive(stack, f->localsplus[i]) < 0) {
return -1;
while (top != f->localsplus) {
--top;
if (gc_visit_stackref_mark_alive(stack, *top) < 0) {
err = -1;
goto exit;
}
}
}
}
exit:
_Py_FOR_EACH_TSTATE_END(interp);
return 0;
return err;
}
#endif // GC_MARK_ALIVE_STACKS
#endif // GC_ENABLE_MARK_ALIVE
Expand Down Expand Up @@ -789,14 +804,23 @@ mark_heap_visitor(const mi_heap_t *heap, const mi_heap_area_t *area,
return true;
}

if (gc_is_alive(op)) {
_PyObject_ASSERT_WITH_MSG(op, gc_get_refs(op) >= 0,
"refcount is too small");

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_is_unreachable(op) && gc_get_refs(op) != 0) {
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.
Expand Down Expand Up @@ -985,7 +1009,7 @@ deduce_unreachable_heap(PyInterpreterState *interp,
#endif

// Visit the thread stacks to account for any deferred references.
gc_visit_thread_stacks(interp);
gc_visit_thread_stacks(interp, state);

// Transitively mark reachable objects by clearing the
// _PyGC_BITS_UNREACHABLE flag.
Expand Down
Loading