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gh-112087: Make list_{subscript, ass_slice, slice} to be thread-safe #115854

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gh-112087: Make list_{subscript, ass_slice, slice} to be thread-safe #115854

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a4bf501
gh-112087: Make list_subscript to be thread-safe
corona10 Feb 21, 2024
ed192d7
Make list_ass_slice to be thread-safe(?)
corona10 Feb 23, 2024
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131 changes: 82 additions & 49 deletions Objects/listobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -506,29 +506,32 @@ list_item(PyObject *aa, Py_ssize_t i)
}

static PyObject *
list_slice(PyListObject *a, Py_ssize_t ilow, Py_ssize_t ihigh)
list_slice_lock_held(PyListObject *a, Py_ssize_t ilow, Py_ssize_t len)
{
PyListObject *np;
PyObject **src, **dest;
Py_ssize_t i, len;
len = ihigh - ilow;
if (len <= 0) {
return PyList_New(0);
}
np = (PyListObject *) list_new_prealloc(len);
if (np == NULL)
PyListObject *np = (PyListObject *) list_new_prealloc(len);
if (np == NULL) {
return NULL;

src = a->ob_item + ilow;
dest = np->ob_item;
for (i = 0; i < len; i++) {
}
PyObject **src = a->ob_item + ilow;
PyObject **dest = np->ob_item;
for (Py_ssize_t i = 0; i < len; i++) {
PyObject *v = src[i];
dest[i] = Py_NewRef(v);
FT_ATOMIC_STORE_PTR_RELAXED(dest[i], Py_NewRef(v));
}
Py_SET_SIZE(np, len);
return (PyObject *)np;
}

static PyObject *
list_slice(PyListObject *a, Py_ssize_t ilow, Py_ssize_t ihigh)
{
Py_ssize_t len = ihigh - ilow;
if (len <= 0) {
return PyList_New(0);
}
return list_slice_lock_held(a, ilow, len);
}

PyObject *
PyList_GetSlice(PyObject *a, Py_ssize_t ilow, Py_ssize_t ihigh)
{
Expand Down Expand Up @@ -695,7 +698,7 @@ list_clear_slot(PyObject *self)
* guaranteed the call cannot fail.
*/
static int
list_ass_slice(PyListObject *a, Py_ssize_t ilow, Py_ssize_t ihigh, PyObject *v)
list_ass_slice_impl(PyListObject *a, Py_ssize_t ilow, Py_ssize_t ihigh, PyObject *v)
{
/* Because [X]DECREF can recursively invoke list operations on
this list, we must postpone all [X]DECREF activity until
Expand All @@ -720,10 +723,10 @@ list_ass_slice(PyListObject *a, Py_ssize_t ilow, Py_ssize_t ihigh, PyObject *v)
else {
if (a == b) {
/* Special case "a[i:j] = a" -- copy b first */
v = list_slice(b, 0, Py_SIZE(b));
v = list_slice_lock_held(b, 0, Py_SIZE(b));
if (v == NULL)
return result;
result = list_ass_slice(a, ilow, ihigh, v);
result = list_ass_slice_impl(a, ilow, ihigh, v);
Py_DECREF(v);
return result;
}
Expand Down Expand Up @@ -800,6 +803,23 @@ list_ass_slice(PyListObject *a, Py_ssize_t ilow, Py_ssize_t ihigh, PyObject *v)
#undef b
}

static int
list_ass_slice(PyListObject *a, Py_ssize_t ilow, Py_ssize_t ihigh, PyObject *v)
{
int ret;
if (v != NULL && PyList_CheckExact(v)) {
Py_BEGIN_CRITICAL_SECTION2(a, v);
ret = list_ass_slice_impl(a, ilow, ihigh, v);
Py_END_CRITICAL_SECTION2();
}
else {
Py_BEGIN_CRITICAL_SECTION(a);
ret = list_ass_slice_impl(a, ilow, ihigh, v);
Py_END_CRITICAL_SECTION();
}
return ret;
}

int
PyList_SetSlice(PyObject *a, Py_ssize_t ilow, Py_ssize_t ihigh, PyObject *v)
{
Expand Down Expand Up @@ -2861,8 +2881,7 @@ list_remove_impl(PyListObject *self, PyObject *value)
int cmp = PyObject_RichCompareBool(obj, value, Py_EQ);
Py_DECREF(obj);
if (cmp > 0) {
if (list_ass_slice(self, i, i+1,
(PyObject *)NULL) == 0)
if (list_ass_slice_impl(self, i, i+1, NULL) == 0)
Py_RETURN_NONE;
return NULL;
}
Expand Down Expand Up @@ -3062,6 +3081,47 @@ static PySequenceMethods list_as_sequence = {
list_inplace_repeat, /* sq_inplace_repeat */
};

static PyObject *
list_slice_step_lock_held(PyListObject *a, Py_ssize_t start, Py_ssize_t step, Py_ssize_t len)
{
PyObject *obj = list_new_prealloc(len);
if (obj == NULL) {
return NULL;
}
PyListObject *np = (PyListObject *)obj;
size_t cur;
Py_ssize_t i;
PyObject **src = a->ob_item;
PyObject **dest = np->ob_item;
for (cur = start, i = 0; i < len;
cur += (size_t)step, i++) {
PyObject *v = src[cur];
FT_ATOMIC_STORE_PTR_RELAXED(dest[i], Py_NewRef(v));
}
Py_SET_SIZE(np, len);
return (PyObject *)np;
}

static PyObject *
list_slice_wrap(PyListObject *aa, Py_ssize_t start, Py_ssize_t stop, Py_ssize_t step)
{
PyObject *res = NULL;
PyListObject *a = (PyListObject *)aa;
Py_BEGIN_CRITICAL_SECTION(a);
Py_ssize_t len = PySlice_AdjustIndices(Py_SIZE(a), &start, &stop, step);
if (len <= 0) {
res = PyList_New(0);
}
else if (step == 1) {
res = list_slice_lock_held(a, start, len);
}
else {
res = list_slice_step_lock_held(a, start, step, len);
}
Py_END_CRITICAL_SECTION();
return res;
}

static PyObject *
list_subscript(PyObject* _self, PyObject* item)
{
Expand All @@ -3076,38 +3136,11 @@ list_subscript(PyObject* _self, PyObject* item)
return list_item((PyObject *)self, i);
}
else if (PySlice_Check(item)) {
Py_ssize_t start, stop, step, slicelength, i;
size_t cur;
PyObject* result;
PyObject* it;
PyObject **src, **dest;

Py_ssize_t start, stop, step;
if (PySlice_Unpack(item, &start, &stop, &step) < 0) {
return NULL;
}
slicelength = PySlice_AdjustIndices(Py_SIZE(self), &start, &stop,
step);

if (slicelength <= 0) {
return PyList_New(0);
}
else if (step == 1) {
return list_slice(self, start, stop);
}
else {
result = list_new_prealloc(slicelength);
if (!result) return NULL;

src = self->ob_item;
dest = ((PyListObject *)result)->ob_item;
for (cur = start, i = 0; i < slicelength;
cur += (size_t)step, i++) {
it = Py_NewRef(src[cur]);
dest[i] = it;
}
Py_SET_SIZE(result, slicelength);
return result;
}
return list_slice_wrap(self, start, stop, step);
}
else {
PyErr_Format(PyExc_TypeError,
Expand Down