8000 gh-112075: Make some `dict` operations thread-safe without GIL by chgnrdv · Pull Request #112247 · python/cpython · GitHub
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gh-112075: Make some dict operations thread-safe without GIL #112247

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gh-112075: Make some dict operations thread-safe without GIL #112247

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c198b07
gh-112075: Make some `dict` operations thread-safe without GIL
chgnrdv Nov 18, 2023
fa6aada
make dict.__repr__ thread-safe with critical section API macro
chgnrdv Nov 18, 2023
12f184f
Merge branch 'main' into make-dict-ops-thread-safe-in-nogil
chgnrdv Nov 18, 2023
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make dict.__repr__ thread-safe with critical section API macro
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@chgnrdv
chgnrdv committed Nov 18, 2023
commit fa6aada6696ce7389f0de8111cd3d9dd5156f8fc
40 changes: 22 additions & 18 deletions Objects/dictobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2506,15 +2506,18 @@ dict_repr(PyDictObject *mp)
PyObject *key = NULL, *value = NULL;
_PyUnicodeWriter writer;
int first;
PyObject *repr = NULL;

i = Py_ReprEnter((PyObject *)mp);
if (i != 0) {
return i > 0 ? PyUnicode_FromString("{...}") : NULL;
}

Py_BEGIN_CRITICAL_SECTION(mp);

if (mp->ma_used == 0) {
Py_ReprLeave((PyObject *)mp);
return PyUnicode_FromString("{}");
repr = PyUnicode_FromString("{}");
goto end;
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I thin this may incorrectly call _PyUnicodeWriter_Dealloc() on an uninitialized writer below if repr is NULL (i.e., if PyUnicode_FromString returns an error).

For these functions with complex control flow, I think it's better to add a wrapper function than try to work Py_BEGIN_CRITICAL_SECTION() calls into the existing control flow. In other words:

  • Rename dict_repr to e.g. dict_repr_impl.
  • Add a new dict_repr that just calls dict_repr_impl under a Py_BEGIN_CRITICAL_SECTION() calls.

}

_PyUnicodeWriter_Init(&writer);
Expand All @@ -2523,7 +2526,7 @@ dict_repr(PyDictObject *mp)
writer.min_length = 1 + 4 + (2 + 4) * (mp->ma_used - 1) + 1;

if (_PyUnicodeWriter_WriteChar(&writer, '{') < 0)
goto error;
goto end;

/* Do repr() on each key+value pair, and insert ": " between them.
Note that repr may mutate the dict. */
Expand All @@ -2539,47 +2542,48 @@ dict_repr(PyDictObject *mp)

if (!first) {
if (_PyUnicodeWriter_WriteASCIIString(&writer, ", ", 2) < 0)
goto error;
goto end;
}
first = 0;

s = PyObject_Repr(key);
if (s == NULL)
goto error;
goto end;
res = _PyUnicodeWriter_WriteStr(&writer, s);
Py_DECREF(s);
if (res < 0)
goto error;
goto end;

if (_PyUnicodeWriter_WriteASCIIString(&writer, ": ", 2) < 0)
goto error;
goto end;

s = PyObject_Repr(value);
if (s == NULL)
goto error;
goto end;
res = _PyUnicodeWriter_WriteStr(&writer, s);
Py_DECREF(s);
if (res < 0)
goto error;
goto end;

Py_CLEAR(key);
Py_CLEAR(value);
}

writer.overallocate = 0;
if (_PyUnicodeWriter_WriteChar(&writer, '}') < 0)
goto error;

Py_ReprLeave((PyObject *)mp);
goto end;

return _PyUnicodeWriter_Finish(&writer);
repr = _PyUnicodeWriter_Finish(&writer);

error:
end:
Py_ReprLeave((PyObject *)mp);
_PyUnicodeWriter_Dealloc(&writer);
Py_XDECREF(key);
Py_XDECREF(value);
return NULL;
if (repr == NULL) {
_PyUnicodeWriter_Dealloc(&writer);
Py_XDECREF(key);
Py_XDECREF(value);
}
Py_END_CRITICAL_SECTION();
return repr;
}

static Py_ssize_t
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0