https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81395
--- Comment #4 from Paolo Carlini <paolo.carlini at oracle dot com> --- Seems weird: -1 means uncommitted (per the comment before _M_set_buffer) and we also set _M_reading? I don't think we do that anywhere else. But it's a long time... Note that I clearly remember somebody suggesting that in fact those _M_reading / _M_writing flags aren't necessary, we could in princinple do without, I even remember seeing a draft patch about that. Certainly, anyway, if we think that uncomitted mode is fine here, there is a way to adjust (or leave alone) both not to cause problems...
