sync()
Returns the current “sync mode” of ios. When sync mode is true, all output is immediately flushed to the underlying operating system and is not buffered by Ruby internally. See also IO#fsync.
f = File.new("testfile") f.sync #=> false
static VALUE rb_io_sync(VALUE io) { rb_io_t *fptr; io = GetWriteIO(io); GetOpenFile(io, fptr); return (fptr->mode & FMODE_SYNC) ? Qtrue : Qfalse; }