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gh-127065: Make methodcaller thread-safe and re-entrant #127245

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223d650
Make methodcalled thread-safe
eendebakpt Nov 23, 2024
b6d454a
check result of PyMem_Malloc
eendebakpt Nov 23, 2024
4ce1233
enable ft
eendebakpt Nov 23, 2024
cf6b79b
fix memory error
eendebakpt Nov 25, 2024
2476ce4
wip
eendebakpt Nov 28, 2024
5ecf876
add tests
eendebakpt Nov 28, 2024
709010d
wip
eendebakpt Nov 28, 2024
6bd2c2e
wip
eendebakpt Nov 28, 2024
8d40552
Merge branch 'main' into methodcaller_ft
eendebakpt Nov 28, 2024
c9e3898
wip
eendebakpt Nov 28, 2024
8ef7a04
fix memory error
eendebakpt Nov 29, 2024
b4f30d3
skip check on zero size for memcpy
eendebakpt Dec 1, 2024
6d06201
📜🤖 Added by blurb_it.
blurb-it[bot] Dec 1, 2024
56cdc1f
Merge branch 'methodcaller_ft' of github.com:eendebakpt/cpython into …
eendebakpt Dec 1, 2024
440eb0c
Merge branch 'main' into methodcaller_ft
eendebakpt Dec 1, 2024
ad66951
review comments
eendebakpt Dec 3, 2024
bc3fe2a
review comments
eendebakpt Dec 3, 2024
e9a1fa6
Update Modules/_operator.c
eendebakpt Dec 6, 2024
00ab654
Update Modules/_operator.c
eendebakpt Dec 6, 2024
5a7344b
review comments
eendebakpt Dec 6, 2024
f9f53fe
Merge branch 'methodcaller_ft' of github.com:eendebakpt/cpython into …
eendebakpt Dec 6, 2024
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13 changes: 13 additions & 0 deletions Lib/test/test_operator.py
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Original file line number Diff line number Diff line change
Expand Up @@ -482,6 +482,8 @@ def bar(self, f=42):
return f
def baz(*args, **kwds):
return kwds['name'], kwds['self']
def return_arguments(self, *args, **kwds):
return args, kwds
a = A()
f = operator.methodcaller('foo')
self.assertRaises(IndexError, f, a)
Expand All @@ -498,6 +500,17 @@ def baz(*args, **kwds):
f = operator.methodcaller('baz', name='spam', self='eggs')
self.assertEqual(f(a), ('spam', 'eggs'))

many_positional_arguments = tuple(range(10))
many_kw_arguments = dict(zip('abcdefghij', range(10)))
f = operator.methodcaller('return_arguments', *many_positional_arguments)
self.assertEqual(f(a), (many_positional_arguments, {}))

f = operator.methodcaller('return_arguments', **many_kw_arguments)
self.assertEqual(f(a), ((), many_kw_arguments))

f = operator.methodcaller('return_arguments', *many_positional_arguments, **many_kw_arguments)
self.assertEqual(f(a), (many_positional_arguments, many_kw_arguments))

def test_inplace(self):
operator = self.module
class C(object):
Expand Down
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2024-12-01-22-28-41.gh-issue-127065.tFpRer.rst
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@@ -0,0 +1 @@
Make :func:`operator.methodcaller` thread-safe and re-entrant safe.
135 changes: 64 additions & 71 deletions Modules/_operator.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1595,36 +1595,59 @@ static PyType_Spec attrgetter_type_spec = {
typedef struct {
PyObject_HEAD
PyObject *name;
PyObject *xargs; // reference to arguments passed in constructor
PyObject *args;
PyObject *kwds;
PyObject **vectorcall_args; /* Borrowed references */
PyObject *vectorcall_kwnames;
Comment on lines 1600 to 1601
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The ownership here seems a bit complicated and I think it can be simplified. As I understand it, vectorcall_kwnames only exists to ensure that some entries in vectorcall_args stay alive.

Instead, I'd suggest:

  • Make PyObject *vectorcall_args a tuple (that holds strong references to its contents as usual)
  • Get rid of vectorcall_kwnames
  • Use _PyTuple_ITEMS for fast access to the contents of the tuple (for memcpy())
  • Visit vectorcall_args in methodcaller_traverse

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The vectorcall_kwnames is needed as an argument for PyObject_VectorcallMethod in methodcaller_vectorcall (https://github.com/python/cpython/blob/main/Modules/_operator.c#L1666), so we cannot get rid of it.

The ownership is not too hard I think: the objects in vectorcall_args have references borrowed from either mc->args or (the keys from) mc->kwds. I added a comment to clarify this.

Making the vectorcall_args a tuple is still an option though. It requires a bit more memory and a tiny bit of computation in the initialization. It would be the C equivalent of vectorcall_args = args + tuple(kwds). I'll work it out in a branch to see how it compares

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Okay, in that case don't worry about it unless you prefer it as a tuple.

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The diff between the two approaches is this:

eendebakpt/cpython@methodcaller_ft...eendebakpt:cpython:methodcaller_ft_v2

What is nice about making vectorcall_args a tuple is that if there are no keyword arguments, we can reuse mc->args. It does require more operations in the construction though.

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I think either approach is fine! My guess is that the vast majority of uses of methodcaller() do not use keyword arguments.

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Running benchmarks shows what is to be expected from the implementations: using a tuple for vectorcall_args is a bit slower in initializing, except when there are no keyword arguments (since then we reuse the arg tuple). Differences are small though.

Since using a tuple leads to cleaner code and the majority of uses is without keywords I slightly prefer the tuple approach. I will open a new PR for it.

vectorcallfunc vectorcall;
} methodcallerobject;

#ifndef Py_GIL_DISABLED

#define _METHODCALLER_MAX_ARGS 8

static PyObject *
methodcaller_vectorcall(
methodcallerobject *mc, PyObject *const *args, size_t nargsf, PyObject* kwnames)
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I think the more common formatting looks like:

methodcaller_vectorcall(methodcallerobject *mc, PyObject *const *args,
                        size_t nargsf, PyObject *kwnames)

{
if (!_PyArg_CheckPositional("methodcaller", PyVectorcall_NARGS(nargsf), 1, 1)
|| !_PyArg_NoKwnames("methodcaller", kwnames)) {
return NULL;
}
assert(mc->vectorcall_args != NULL);

Py_ssize_t number_of_arguments = PyTuple_GET_SIZE(mc->args) +
(mc->vectorcall_kwnames? PyTuple_GET_SIZE(mc->vectorcall_kwnames):0);

PyObject *tmp_args[_METHODCALLER_MAX_ARGS];
tmp_args[0] = args[0];
assert(1 + number_of_arguments <= _METHODCALLER_MAX_ARGS);
memcpy(tmp_args + 1, mc->vectorcall_args, sizeof(PyObject *) * number_of_arguments);

PyObject *result = PyObject_VectorcallMethod(
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Up to you, but I'd write this without the temporary result variable like:

return PyObject_VectorcallMethod(...);

mc->name, tmp_args,
(1 + PyTuple_GET_SIZE(mc->args)) | PY_VECTORCALL_ARGUMENTS_OFFSET,
mc->vectorcall_kwnames);

return result;
}

static int _methodcaller_initialize_vectorcall(methodcallerobject* mc)
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Suggested change
static int _methodcaller_initialize_vectorcall(methodcallerobject* mc)
static int
_methodcaller_initialize_vectorcall(methodcallerobject *mc)

{
PyObject* args = mc->xargs;
PyObject* args = mc->args;
PyObject* kwds = mc->kwds;

Py_ssize_t nargs = PyTuple_GET_SIZE(args);
assert(nargs > 0);
mc->vectorcall_args = PyMem_Calloc(
nargs + (kwds ? PyDict_Size(kwds) : 0),
sizeof(PyObject*));
if (!mc->vectorcall_args) {
PyErr_NoMemory();
return -1;
}
/* The first item of vectorcall_args will be filled with obj later */
if (nargs > 1) {
memcpy(mc->vectorcall_args, PySequence_Fast_ITEMS(args),
memcpy(mc->vectorcall_args, PySequence_Fast_ITEMS(args),
nargs * sizeof(PyObject*));
}
if (kwds) {
if (kwds && PyDict_Size(kwds)) {
const Py_ssize_t nkwds = PyDict_Size(kwds);

mc->vectorcall_kwnames = PyTuple_New(nkwds);
if (!mc->vectorcall_kwnames) {
return -1;
Expand All @@ -1640,33 +1663,10 @@ static int _methodcaller_initialize_vectorcall(methodcallerobject* mc)
else {
mc->vectorcall_kwnames = NULL;
}
return 1;
}


static PyObject *
methodcaller_vectorcall(
methodcallerobject *mc, PyObject *const *args, size_t nargsf, PyObject* kwnames)
{
if (!_PyArg_CheckPositional("methodcaller", PyVectorcall_NARGS(nargsf), 1, 1)
|| !_PyArg_NoKwnames("methodcaller", kwnames)) {
return NULL;
}
if (mc->vectorcall_args == NULL) {
if (_methodcaller_initialize_vectorcall(mc) < 0) {
return NULL;
}
}
mc->vectorcall = (vectorcallfunc)methodcaller_vectorcall;

assert(mc->vectorcall_args != 0);
mc->vectorcall_args[0] = args[0];
return PyObject_VectorcallMethod(
mc->name, mc->vectorcall_args,
(PyTuple_GET_SIZE(mc->xargs)) | PY_VECTORCALL_ARGUMENTS_OFFSET,
mc->vectorcall_kwnames);
return 1;
}
#endif


/* AC 3.5: variable number of arguments, not currently support by AC */
static PyObject *
Expand Down Expand Up @@ -1700,19 +1700,25 @@ methodcaller_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
_PyUnicode_InternMortal(interp, &name);
mc->name = name;

mc->xargs = Py_XNewRef(args); // allows us to use borrowed references
mc->args = PyTuple_GetSlice(args, 1, PyTuple_GET_SIZE(args));
if (mc->args == NULL) {
Py_DECREF(mc);
return NULL;
}
mc->kwds = Py_XNewRef(kwds);
mc->vectorcall_args = 0;


#ifdef Py_GIL_DISABLED
// gh-127065: The current implementation of methodcaller_vectorcall
// is not thread-safe because it modifies the `vectorcall_args` array,
// which is shared across calls.
mc->vectorcall = NULL;
#else
mc->vectorcall = (vectorcallfunc)methodcaller_vectorcall;
#endif
mc->vectorcall_args = NULL;
mc->vectorcall_kwnames = NULL;

Py_ssize_t vectorcall_size = PyTuple_GET_SIZE(args)
+ (kwds ? PyDict_Size(kwds) : 0);
if (vectorcall_size < (_METHODCALLER_MAX_ARGS)) {
if (_methodcaller_initialize_vectorcall(mc) < 0) {
Py_XDECREF(mc->args);
Py_XDECREF(mc->kwds);
return NULL;
}
}

PyObject_GC_Track(mc);
return (PyObject *)mc;
Expand All @@ -1722,11 +1728,11 @@ static void
methodcaller_clear(methodcallerobject *mc)
{
Py_CLEAR(mc->name);
Py_CLEAR(mc->xargs);
Py_CLEAR(mc->args);
Py_CLEAR(mc->kwds);
if (mc->vectorcall_args != NULL) {
PyMem_Free(mc->vectorcall_args);
mc->vectorcall_args = 0;
mc->vectorcall_args = NULL;
Py_CLEAR(mc->vectorcall_kwnames);
}
}
Expand All @@ -1745,7 +1751,7 @@ static int
methodcaller_traverse(methodcallerobject *mc, visitproc visit, void *arg)
{
Py_VISIT(mc->name);
Py_VISIT(mc->xargs);
Py_VISIT(mc->args);
Py_VISIT(mc->kwds);
Py_VISIT(Py_TYPE(mc));
return 0;
Expand All @@ -1765,15 +1771,7 @@ methodcaller_call(methodcallerobject *mc, PyObject *args, PyObject *kw)
if (method == NULL)
return NULL;


PyObject *cargs = PyTuple_GetSlice(mc->xargs, 1, PyTuple_GET_SIZE(mc->xargs));
if (cargs == NULL) {
Py_DECREF(method);
return NULL;
}

result = PyObject_Call(method, cargs, mc->kwds);
Py_DECREF(cargs);
result = PyObject_Call(method, mc->args, mc->kwds);
Py_DECREF(method);
return result;
}
Expand All @@ -1791,7 +1789,7 @@ methodcaller_repr(methodcallerobject *mc)
}

numkwdargs = mc->kwds != NULL ? PyDict_GET_SIZE(mc->kwds) : 0;
numposargs = PyTuple_GET_SIZE(mc->xargs) - 1;
numposargs = PyTuple_GET_SIZE(mc->args);
numtotalargs = numposargs + numkwdargs;

if (numtotalargs == 0) {
Expand All @@ -1807,7 +1805,7 @@ methodcaller_repr(methodcallerobject *mc)
}

for (i = 0; i < numposargs; ++i) {
PyObject *onerepr = PyObject_Repr(PyTuple_GET_ITEM(mc->xargs, i+1));
PyObject *onerepr = PyObject_Repr(PyTuple_GET_ITEM(mc->args, i));
if (onerepr == NULL)
goto done;
PyTuple_SET_ITEM(argreprs, i, onerepr);
Expand Down Expand Up @@ -1859,14 +1857,14 @@ methodcaller_reduce(methodcallerobject *mc, PyObject *Py_UNUSED(ignored))
{
if (!mc->kwds || PyDict_GET_SIZE(mc->kwds) == 0) {
Py_ssize_t i;
Py_ssize_t newarg_size = PyTuple_GET_SIZE(mc->xargs);
PyObject *newargs = PyTuple_New(newarg_size);
Py_ssize_t callargcount = PyTuple_GET_SIZE(mc->args);
PyObject *newargs = PyTuple_New(1 + callargcount);
if (newargs == NULL)
return NULL;
PyTuple_SET_ITEM(newargs, 0, Py_NewRef(mc->name));
for (i = 1; i < newarg_size; ++i) {
PyObject *arg = PyTuple_GET_ITEM(mc->xargs, i);
PyTuple_SET_ITEM(newargs, i, Py_NewRef(arg));
for (i = 0; i < callargcount; ++i) {
PyObject *arg = PyTuple_GET_ITEM(mc->args, i);
PyTuple_SET_ITEM(newargs, i + 1, Py_NewRef(arg));
}
return Py_BuildValue("ON", Py_TYPE(mc), newargs);
}
Expand All @@ -1884,12 +1882,7 @@ methodcaller_reduce(methodcallerobject *mc, PyObject *Py_UNUSED(ignored))
constructor = PyObject_VectorcallDict(partial, newargs, 2, mc->kwds);

Py_DECREF(partial);
PyObject *args = PyTuple_GetSlice(mc->xargs, 1, PyTuple_GET_SIZE(mc->xargs));
if (!args) {
Py_DECREF(constructor);
return NULL;
}
return Py_BuildValue("NO", constructor, args);
return Py_BuildValue("NO", constructor, mc->args);
}
}

Expand Down
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