gh-119506: fix _io.TextIOWrapper.write() write during flush

Lib/test/test_io.py

@@ -4016,6 +4016,28 @@ def write(self, data):
  t.write("x"*chunk_size)
  self.assertEqual([b"abcdef", b"ghi", b"x"*chunk_size], buf._write_stack)
 
+ def test_issue119506(self):
+ chunk_size = 8192
+
+ class MockIO(self.MockRawIO):
+ written = False
+ def write(self, data):
+ if not self.written:
+ self.written = True
+ t.write("middle")
+ return super().write(data)
+
+ buf = MockIO()
+ t = self.TextIOWrapper(buf)
+ t.write("abc")
+ t.write("def")
+ # writing data which size >= chunk_size cause flushing buffer before write.
+ t.write("g" * chunk_size)
+ t.flush()
+
+ self.assertEqual([b"abcdef", b"middle", b"g"*chunk_size],
+ buf._write_stack)
+
 
 class PyTextIOWrapperTest(TextIOWrapperTest):
  io = pyio

Misc/NEWS.d/next/Library/2024-05-24-14-32-24.gh-issue-119506.-nMNqq.rst

@@ -0,0 +1 @@
+Fix :meth:`!io.TextIOWrapper.write` method breaks internal buffer when the method is called again during flushing internal buffer.

Modules/_io/textio.c

@@ -1719,16 +1719,26 @@ _io_TextIOWrapper_write_impl(textio *self, PyObject *text)
  bytes_len = PyBytes_GET_SIZE(b);
  }
 
- if (self->pending_bytes == NULL){
- self->pending_bytes_count = 0;
- self->pending_bytes = b;
- }
- else if (self->pending_bytes_count + bytes_len > self->chunk_size){
- // Prevent to concatenate more than chunk_size data.
- if (_textiowrapper_writeflush(self) < 0){
- Py_DECREF(b);
- return NULL;
+ // We should avoid concatinating huge data.
+ // Flush the buffer before adding b to the buffer if b is not small.
+ // https://github.com/python/cpython/issues/87426
+ if (bytes_len >= self->chunk_size){
+ // _textiowrapper_writeflush() calls buffer.write().
+ // self->pending_bytes can be appended during buffer->write()
+ // or other thread.
+ // We need to loop until buffer becomes empty.
+ // https://github.com/python/cpython/issues/118138
+ // https://github.com/python/cpython/issues/119506
+ while (self->pending_bytes != NULL){
+ if (_textiowrapper_writeflush(self) < 0){
+ Py_DECREF(b);
+ return NULL;
+ }
  }
+ }
+
+ if (self->pending_bytes == NULL){
+ assert(self->pending_bytes_count == 0);
  self->pending_bytes = b;
  }
  else if (!PyList_CheckExact(self->pending_bytes)){
@@ -1737,6 +1747,9 @@ _io_TextIOWrapper_write_impl(textio *self, PyObject *text)
  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;