`@_lock_ios` is used to skip `lock()` when a IOStream was opened with `open(; lock=false)` https://github.com/JuliaLang/julia/blob/fc02458492c60f6527245c6991f729c2a986f666/base/iostream.jl#L396-L399 But reading non-UInt8 types seem to always lock the file regardless: https://github.com/JuliaLang/julia/blob/fc02458492c60f6527245c6991f729c2a986f666/base/iostream.jl#L405-L408