Fix thread safety in StringIO.

Author: ZeroIntensity

Modules/_io/stringio.c

@@ -79,6 +79,7 @@ static int _io_StringIO___init__(PyObject *self, PyObject *args, PyObject *kwarg
 static int
 resize_buffer(stringio *self, size_t size)
 {
+    _Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED(self);
     /* Here, unsigned types are used to avoid dealing with signed integer
        overflow, which is undefined in C. */
     size_t alloc = self->buf_size;
@@ -131,6 +132,7 @@ resize_buffer(stringio *self, size_t size)
 static PyObject *
 make_intermediate(stringio *self)
 {
+    _Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED(self);
     PyObject *intermediate = PyUnicodeWriter_Finish(self->writer);
     self->writer = NULL;
     self->state = STATE_REALIZED;
@@ -153,6 +155,7 @@ make_intermediate(stringio *self)
 static int
 realize(stringio *self)
 {
+    _Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED(self);
     Py_ssize_t len;
     PyObject *intermediate;
 
@@ -188,6 +191,7 @@ realize(stringio *self)
 static Py_ssize_t
 write_str(stringio *self, PyObject *obj)
 {
+    _Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED(self);
     Py_ssize_t len;
     PyObject *decoded = NULL;
 
@@ -355,6 +359,7 @@ _io_StringIO_read_impl(stringio *self, Py_ssize_t size)
 static PyObject *
 _stringio_readline(stringio *self, Py_ssize_t limit)
 {
+    _Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED(self);
     Py_UCS4 *start, *end, old_char;
     Py_ssize_t len, consumed;
 
@@ -404,8 +409,9 @@ _io_StringIO_readline_impl(stringio *self, Py_ssize_t size)
 }
 
 static PyObject *
-stringio_iternext(PyObject *op)
+stringio_iternext_lock_held(PyObject *op)
 {
+    _Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED(op);
     PyObject *line;
     stringio *self = stringio_CAST(op);
 
@@ -441,6 +447,16 @@ stringio_iternext(PyObject *op)
     return line;
 }
 
+static PyObject *
+stringio_iternext(PyObject *op)
+{
+    PyObject *res;
+    Py_BEGIN_CRITICAL_SECTION(op);
+    res = stringio_iternext_lock_held(op);
+    Py_END_CRITICAL_SECTION();
+    return res;
+}
+
 /*[clinic input]
 @critical_section
 _io.StringIO.truncate