8000 [3.14] gh-134908: Protect `textiowrapper_iternext` with critical sect… · python/cpython@428b0ca · GitHub
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    [3.14] gh-134908: Protect textiowrapper_iternext with critical section (gh-134910) (gh-135039)
    The `textiowrapper_iternext` function called `_textiowrapper_writeflush`, but did not use a critical section, making it racy in free-threaded builds. (cherry picked from commit 44fb7c3) Co-authored-by: Duane Griffin <duaneg@dghda.com>
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    ‎Lib/test/test_io.py

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    Original file line numberDiff line numberDiff line change
    @@ -1062,6 +1062,37 @@ def flush(self):
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    # Silence destructor error
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    R.flush = lambda self: None
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    1065+
    @threading_helper.requires_working_threading()
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    def test_write_readline_races(self):
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    # gh-134908: Concurrent iteration over a file caused races
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    thread_count = 2
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    write_count = 100
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    read_count = 100
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    def writer(file, barrier):
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    barrier.wait()
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    for _ in range(write_count):
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    file.write("x")
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    1077+
    def reader(file, barrier):
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    barrier.wait()
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    for _ in range(read_count):
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    for line in file:
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    self.assertEqual(line, "")
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    1083+
    with self.open(os_helper.TESTFN, "w+") as f:
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    barrier = threading.Barrier(thread_count + 1)
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    reader = threading.Thread(target=reader, args=(f, barrier))
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    writers = [threading.Thread(target=writer, args=(f, barrier))
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    for _ in range(thread_count)]
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    with threading_helper.catch_threading_exception() as cm:
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    with threading_helper.start_threads(writers + [reader]):
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    pass
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    self.assertIsNone(cm.exc_type)
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    1093+
    self.assertEqual(os.stat(os_helper.TESTFN).st_size,
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    write_count * thread_count)
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    10651096

    10661097
    class CIOTest(IOTest):
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    ‎Misc/NEWS.d/next/Core_and_Builtins/2025-05-30-15-56-19.gh-issue-134908.3a7PxM.rst

    Lines changed: 1 addition & 0 deletions
    Original file line numberDiff line numberDiff line change
    @@ -0,0 +1 @@
    1+
    Fix crash when iterating over lines in a text file on the :term:`free threaded <free threading>` build.

    ‎Modules/_io/textio.c

    Lines changed: 14 additions & 1 deletion
    Original file line numberDiff line numberDiff line change
    @@ -1578,6 +1578,8 @@ _io_TextIOWrapper_detach_impl(textio *self)
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    static int
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    _textiowrapper_writeflush(textio *self)
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    {
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    _Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED(self);
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    15811583
    if (self->pending_bytes == NULL)
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    return 0;
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    @@ -3173,8 +3175,9 @@ _io_TextIOWrapper_close_impl(textio *self)
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    }
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    static PyObject *
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    textiowrapper_iternext(PyObject *op)
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    textiowrapper_iternext_lock_held(PyObject *op)
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    {
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    _Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED(op);
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    PyObject *line;
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    textio *self = textio_CAST(op);
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    @@ -3210,6 +3213,16 @@ textiowrapper_iternext(PyObject *op)
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    return line;
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    }
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    static PyObject *
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    textiowrapper_iternext(PyObject *op)
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    {
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    PyObject *result;
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    Py_BEGIN_CRITICAL_SECTION(op);
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    result = textiowrapper_iternext_lock_held(op);
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    Py_END_CRITICAL_SECTION();
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    return result;
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    }
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    32133226
    /*[clinic input]
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    @critical_section
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    @getter

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