OutputStream.flush

Forces a write of all user-space buffered data for the given stream. Will block during the operation. Closing the stream will implicitly cause a flush.

This function is optional for inherited classes.

If cancellable is not null, then the operation can be cancelled by triggering the cancellable object from another thread. If the operation was cancelled, the error [gio.types.IOErrorEnum.Cancelled] will be returned.