If GMemoryOutputStream or GMemoryInputStream are extended by other classes, and the read or write methods overriden, then attempts to use async I/O methods on these child classes do not behave as expected, as the g_memory_input_stream_read_async and g_memory_output_stream_write_async methods directly invoke their non-async versions, rather than going through the vtable.

E.g. in g_memory_output_stream_write_async:

nwritten = g_memory_output_stream_write (...)

and in g_memory_input_stream_read_async:

nread = g_memory_input_stream_read (...)

Presumably these, and other calls of g_memory_{out,in}put_stream_read in the 2 classes, should be replaced with indirect vtable calls, so that overrides can work.