https://github.com/python/cpython/commit/6bad84d64c63facc5f93a1ea0a053f620e05cb92 commit: 6bad84d64c63facc5f93a1ea0a053f620e05cb92 branch: 3.15 author: Miss Islington (bot) <[email protected]> committer: StanFromIreland <[email protected]> date: 2026-06-24T12:14:01Z summary:
[3.15] gh-151814: Fix unbounded memory growth from repeated empty writes to `io.TextIOWrapper` (GH-151817) (cherry picked from commit c61307222e18bfa06691d53e3ad336c46f432de0) Co-authored-by: Stan Ulbrych <[email protected]> files: A Misc/NEWS.d/next/Library/2026-06-20-21-15-13.gh-issue-151814.OIbgsO.rst M Modules/_io/textio.c diff --git a/Misc/NEWS.d/next/Library/2026-06-20-21-15-13.gh-issue-151814.OIbgsO.rst b/Misc/NEWS.d/next/Library/2026-06-20-21-15-13.gh-issue-151814.OIbgsO.rst new file mode 100644 index 000000000000000..1365fb4d8edb1d2 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2026-06-20-21-15-13.gh-issue-151814.OIbgsO.rst @@ -0,0 +1,2 @@ +Fix unbounded memory growth in :class:`io.TextIOWrapper` when repeatedly +writing an empty string. diff --git a/Modules/_io/textio.c b/Modules/_io/textio.c index 1547c04cdf06afa..aea21e391dd96e8 100644 --- a/Modules/_io/textio.c +++ b/Modules/_io/textio.c @@ -1755,32 +1755,38 @@ _io_TextIOWrapper_write_impl(textio *self, PyObject *text) } } - if (self->pending_bytes == NULL) { - assert(self->pending_bytes_count == 0); - self->pending_bytes = b; - } - else if (!PyList_CheckExact(self->pending_bytes)) { - PyObject *list = PyList_New(2); - if (list == NULL) { + if (bytes_len > 0) { + if (self->pending_bytes == NULL) { + assert(self->pending_bytes_count == 0); + self->pending_bytes = b; + } + else if (!PyList_CheckExact(self->pending_bytes)) { + PyObject *list = PyList_New(2); + if (list == NULL) { + Py_DECREF(b); + return NULL; + } + // Since Python 3.12, allocating GC object won't trigger GC and release + // GIL. See https://github.com/python/cpython/issues/97922 + assert(!PyList_CheckExact(self->pending_bytes)); + PyList_SET_ITEM(list, 0, self->pending_bytes); + PyList_SET_ITEM(list, 1, b); + self->pending_bytes = list; + } + else { + if (PyList_Append(self->pending_bytes, b) < 0) { + Py_DECREF(b); + return NULL; + } Py_DECREF(b); - return NULL; } - // Since Python 3.12, allocating GC object won't trigger GC and release - // GIL. See https://github.com/python/cpython/issues/97922 - assert(!PyList_CheckExact(self->pending_bytes)); - PyList_SET_ITEM(list, 0, self->pending_bytes); - PyList_SET_ITEM(list, 1, b); - self->pending_bytes = list; + + self->pending_bytes_count += bytes_len; } else { - if (PyList_Append(self->pending_bytes, b) < 0) { - Py_DECREF(b); - return NULL; - } Py_DECREF(b); } - self->pending_bytes_count += bytes_len; if (self->pending_bytes_count >= self->chunk_size || needflush || text_needflush) { if (_textiowrapper_writeflush(self) < 0) _______________________________________________ Python-checkins mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3//lists/python-checkins.python.org Member address: [email protected]
