These are great reads for how it was implemented. As for how late see above. https://www.bsdcan.org/2012/schedule/attachments/195_locking.pdf https://www.bsdca

These are great reads for how it was implemented. As for how late see above. https://www.bsdcan.org/2012/schedule/attachments/195_locking.pdf https://www.bsdcan.org/2012/schedule/attachments/195_locking... https://books.google.com/books?id=aY1pBAAAQBAJ&printsec=frontcover&dq=design+and+implementation+of+the+freebsd+operating+system&hl=en&sa=X&ved=0ahUKEwiH06vohqzOAhVDTCYKHavvBCYQ6AEIHDAA#v=onepage&q=freebsd%20mutex%20implementation&f=false https://books.google.com/books?id=aY1pBAAAQBAJ&printsec=fron...