Are the read and write functions of Serial thread-safe?

[Mq-b]

Are the read and write functions of Serial thread-safe?
Because I want to read and write the serial port is independent, I should not need protection? But I'm not sure if the object itself is thread-safe?

[Mq-b]

https://github.com/wjwwood/serial/blob/57f7277/src/impl/unix.cc#L1048-L1082

I saw pthread_mutex in the source code but I'm still not sure how much of a guarantee there is?