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gh-139871: Optimize bytearray unique bytes iconcat #141862

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gh-139871: Optimize bytearray unique bytes iconcat #141862

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gh-139871: Optimize bytearray unique bytes iconcat
cmaloney Nov 18, 2025
08364c1
Apply suggestions from code review
cmaloney Nov 24, 2025
70c15bf
Switch from comment to assertion
cmaloney Nov 24, 2025
614e743
Call take_bytes directly
cmaloney Dec 3, 2025
c5e9da6
Update Objects/bytearrayobject.c
cmaloney Dec 3, 2025
e6fd741
Borrow -> Borrowed
cmaloney Dec 3, 2025
fe114fb
Merge branch 'main' into ba_tb_concat
cmaloney Dec 15, 2025
c689a0a
Use PyUnstable_Object_IsUniqueReferencedTemporary
cmaloney Dec 15, 2025
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54 changes: 41 additions & 13 deletions Objects/bytearrayobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -333,6 +333,42 @@ bytearray_iconcat_lock_held(PyObject *op, PyObject *other)
_Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED(op);
PyByteArrayObject *self = _PyByteArray_CAST(op);

// optimization: Avoid copying the bytes coming in when possible.
if (self->ob_alloc == 0 && _PyObject_IsUniquelyReferenced(other)) {
assert(_Py_IsImmortal(self->ob_bytes_object));
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if (!_canresize(self)) {
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return NULL;
}

/* Get the bytes out of the temporary bytearray.
* Just returning other doesn't work as __init__ calls this and can't
* change self. */
if (PyByteArray_CheckExact(other)) {
PyObject *taken = PyObject_CallMethodNoArgs(other,
&_Py_ID(take_bytes));
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@colesbury colesbury Nov 25, 2025

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This looks unsafe to me. If you call a method, you may invalidate the assumptions you verified earlier

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@vstinner vstinner Nov 26, 2025

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Maybe call bytearray_take_bytes_impl() directly to reduce the risk of side effects? And you can check again _PyObject_IsUniquelyReferenced() in an assertion.

if (taken == NULL) {
return NULL;
}
// Avoid Py_INCREF needed for argument case.
Py_ssize_t size = Py_SIZE(taken);
self->ob_bytes_object = taken;
bytearray_reinit_from_bytes(self, size, size);
return Py_NewRef(self);
}

if (PyBytes_CheckExact(other)) {
Py_ssize_t size = Py_SIZE(other);
self->ob_bytes_object = other;
bytearray_reinit_from_bytes(self, size, size);
Py_INCREF(self->ob_bytes_object);

// Caller has a reference still and its decref will return
// bytes to be uniquely referenced.
assert(Py_REFCNT(self->ob_bytes_object) == 2);
return Py_NewRef(self);
}
}

Py_buffer vo;
if (PyObject_GetBuffer(other, &vo, PyBUF_SIMPLE) != 0) {
PyErr_Format(PyExc_TypeError, "can't concat %.100s to %.100s",
Expand Down Expand Up @@ -977,22 +1013,14 @@ bytearray___init___impl(PyByteArrayObject *self, PyObject *arg,
}
}

/* Use the buffer API */
/* Use the buffer API. Defer to iconcat which optimizes. */
if (PyObject_CheckBuffer(arg)) {
Py_ssize_t size;
Py_buffer view;
if (PyObject_GetBuffer(arg, &view, PyBUF_FULL_RO) < 0)
PyObject *new = bytearray_iconcat((PyObject *)self, arg);
if (new == NULL) {
return -1;
size = view.len;
if (PyByteArray_Resize((PyObject *)self, size) < 0) goto fail;
if (PyBuffer_ToContiguous(PyByteArray_AS_STRING(self),
&view, size, 'C') < 0)
goto fail;
PyBuffer_Release(&view);
}
Py_DECREF(new);
return 0;
fail:
PyBuffer_Release(&view);
return -1;
}

if (PyList_CheckExact(arg) || PyTuple_CheckExact(arg)) {
Expand Down
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