https://github.com/python/cpython/commit/8db8fc9b51060b61d14fbe6aa0f2e2591292279e
commit: 8db8fc9b51060b61d14fbe6aa0f2e2591292279e
branch: main
author: Sam Gross <[email protected]>
committer: colesbury <[email protected]>
date: 2026-02-23T09:32:16-05:00
summary:
gh-144777: Fix data races in IncrementalNewlineDecoder (gh-144971)
files:
A Misc/NEWS.d/next/Library/2026-02-18-13-45-00.gh-issue-144777.R97q0a.rst
M Lib/test/test_free_threading/test_io.py
M Modules/_io/clinic/textio.c.h
M Modules/_io/textio.c
diff --git a/Lib/test/test_free_threading/test_io.py
b/Lib/test/test_free_threading/test_io.py
index c67aaff31b3f5b..8a0ad30c4bc770 100644
--- a/Lib/test/test_free_threading/test_io.py
+++ b/Lib/test/test_free_threading/test_io.py
@@ -1,11 +1,15 @@
+import codecs
import io
import _pyio as pyio
import threading
from unittest import TestCase
from test.support import threading_helper
+from test.support.threading_helper import run_concurrently
from random import randint
from sys import getsizeof
+threading_helper.requires_working_threading(module=True)
+
class ThreadSafetyMixin:
# Test pretty much everything that can break under free-threading.
@@ -115,3 +119,54 @@ class CBytesIOTest(ThreadSafetyMixin, TestCase):
class PyBytesIOTest(ThreadSafetyMixin, TestCase):
ioclass = pyio.BytesIO
+
+
+class IncrementalNewlineDecoderTest(TestCase):
+ def make_decoder(self):
+ utf8_decoder = codecs.getincrementaldecoder('utf-8')()
+ return io.IncrementalNewlineDecoder(utf8_decoder, translate=True)
+
+ def test_concurrent_reset(self):
+ decoder = self.make_decoder()
+
+ def worker():
+ for _ in range(100):
+ decoder.reset()
+
+ run_concurrently(worker_func=worker, nthreads=2)
+
+ def test_concurrent_decode(self):
+ decoder = self.make_decoder()
+
+ def worker():
+ for _ in range(100):
+ decoder.decode(b"line\r\n", final=False)
+
+ run_concurrently(worker_func=worker, nthreads=2)
+
+ def test_concurrent_getstate_setstate(self):
+ decoder = self.make_decoder()
+ state = decoder.getstate()
+
+ def getstate_worker():
+ for _ in range(100):
+ decoder.getstate()
+
+ def setstate_worker():
+ for _ in range(100):
+ decoder.setstate(state)
+
+ run_concurrently([getstate_worker] * 2 + [setstate_worker] * 2)
+
+ def test_concurrent_decode_and_reset(self):
+ decoder = self.make_decoder()
+
+ def decode_worker():
+ for _ in range(100):
+ decoder.decode(b"line\r\n", final=False)
+
+ def reset_worker():
+ for _ in range(100):
+ decoder.reset()
+
+ run_concurrently([decode_worker] * 2 + [reset_worker] * 2)
diff --git
a/Misc/NEWS.d/next/Library/2026-02-18-13-45-00.gh-issue-144777.R97q0a.rst
b/Misc/NEWS.d/next/Library/2026-02-18-13-45-00.gh-issue-144777.R97q0a.rst
new file mode 100644
index 00000000000000..fd720bfd3f3da6
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-02-18-13-45-00.gh-issue-144777.R97q0a.rst
@@ -0,0 +1 @@
+Fix data races in :class:`io.IncrementalNewlineDecoder` in the
:term:`free-threaded build`.
diff --git a/Modules/_io/clinic/textio.c.h b/Modules/_io/clinic/textio.c.h
index 128a5ad1678f26..3898a9c2982436 100644
--- a/Modules/_io/clinic/textio.c.h
+++ b/Modules/_io/clinic/textio.c.h
@@ -430,7 +430,9 @@ _io_IncrementalNewlineDecoder_decode(PyObject *self,
PyObject *const *args, Py_s
goto exit;
}
skip_optional_pos:
+ Py_BEGIN_CRITICAL_SECTION(self);
return_value = _io_IncrementalNewlineDecoder_decode_impl((nldecoder_object
*)self, input, final);
+ Py_END_CRITICAL_SECTION();
exit:
return return_value;
@@ -450,7 +452,13 @@
_io_IncrementalNewlineDecoder_getstate_impl(nldecoder_object *self);
static PyObject *
_io_IncrementalNewlineDecoder_getstate(PyObject *self, PyObject
*Py_UNUSED(ignored))
{
- return _io_IncrementalNewlineDecoder_getstate_impl((nldecoder_object
*)self);
+ PyObject *return_value = NULL;
+
+ Py_BEGIN_CRITICAL_SECTION(self);
+ return_value =
_io_IncrementalNewlineDecoder_getstate_impl((nldecoder_object *)self);
+ Py_END_CRITICAL_SECTION();
+
+ return return_value;
}
PyDoc_STRVAR(_io_IncrementalNewlineDecoder_setstate__doc__,
@@ -470,7 +478,9 @@ _io_IncrementalNewlineDecoder_setstate(PyObject *self,
PyObject *state)
{
PyObject *return_value = NULL;
+ Py_BEGIN_CRITICAL_SECTION(self);
return_value =
_io_IncrementalNewlineDecoder_setstate_impl((nldecoder_object *)self, state);
+ Py_END_CRITICAL_SECTION();
return return_value;
}
@@ -489,7 +499,13 @@ _io_IncrementalNewlineDecoder_reset_impl(nldecoder_object
*self);
static PyObject *
_io_IncrementalNewlineDecoder_reset(PyObject *self, PyObject
*Py_UNUSED(ignored))
{
- return _io_IncrementalNewlineDecoder_reset_impl((nldecoder_object *)self);
+ PyObject *return_value = NULL;
+
+ Py_BEGIN_CRITICAL_SECTION(self);
+ return_value = _io_IncrementalNewlineDecoder_reset_impl((nldecoder_object
*)self);
+ Py_END_CRITICAL_SECTION();
+
+ return return_value;
}
PyDoc_STRVAR(_io_TextIOWrapper___init____doc__,
@@ -1312,4 +1328,4 @@ _io_TextIOWrapper__CHUNK_SIZE_set(PyObject *self,
PyObject *value, void *Py_UNUS
return return_value;
}
-/*[clinic end generated code: output=30404271a1151056 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=c38e6cd5ff4b7eea input=a9049054013a1b77]*/
diff --git a/Modules/_io/textio.c b/Modules/_io/textio.c
index f9881952561292..347bfe976619e8 100644
--- a/Modules/_io/textio.c
+++ b/Modules/_io/textio.c
@@ -519,6 +519,7 @@ _PyIncrementalNewlineDecoder_decode(PyObject *myself,
}
/*[clinic input]
+@critical_section
_io.IncrementalNewlineDecoder.decode
input: object
final: bool = False
@@ -527,18 +528,19 @@ _io.IncrementalNewlineDecoder.decode
static PyObject *
_io_IncrementalNewlineDecoder_decode_impl(nldecoder_object *self,
PyObject *input, int final)
-/*[clinic end generated code: output=0d486755bb37a66e input=90e223c70322c5cd]*/
+/*[clinic end generated code: output=0d486755bb37a66e input=9475d16a73168504]*/
{
return _PyIncrementalNewlineDecoder_decode((PyObject *) self, input,
final);
}
/*[clinic input]
+@critical_section
_io.IncrementalNewlineDecoder.getstate
[clinic start generated code]*/
static PyObject *
_io_IncrementalNewlineDecoder_getstate_impl(nldecoder_object *self)
-/*[clinic end generated code: output=f0d2c9c136f4e0d0 input=f8ff101825e32e7f]*/
+/*[clinic end generated code: output=f0d2c9c136f4e0d0 input=dc3e1f27aa850f12]*/
{
PyObject *buffer;
unsigned long long flag;
@@ -576,6 +578,7 @@
_io_IncrementalNewlineDecoder_getstate_impl(nldecoder_object *self)
}
/*[clinic input]
+@critical_section
_io.IncrementalNewlineDecoder.setstate
state: object
/
@@ -584,7 +587,7 @@ _io.IncrementalNewlineDecoder.setstate
static PyObject *
_io_IncrementalNewlineDecoder_setstate_impl(nldecoder_object *self,
PyObject *state)
-/*[clinic end generated code: output=09135cb6e78a1dc8 input=c53fb505a76dbbe2]*/
+/*[clinic end generated code: output=09135cb6e78a1dc8 input=275fd3982d2b08cb]*/
{
PyObject *buffer;
unsigned long long flag;
@@ -614,12 +617,13 @@
_io_IncrementalNewlineDecoder_setstate_impl(nldecoder_object *self,
}
/*[clinic input]
+@critical_section
_io.IncrementalNewlineDecoder.reset
[clinic start generated code]*/
static PyObject *
_io_IncrementalNewlineDecoder_reset_impl(nldecoder_object *self)
-/*[clinic end generated code: output=32fa40c7462aa8ff input=728678ddaea776df]*/
+/*[clinic end generated code: output=32fa40c7462aa8ff input=31bd8ae4e36cec83]*/
{
CHECK_INITIALIZED_DECODER(self);
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