[joeldo]

My understanding is that an efficient lock would require hardware support, which is surfaced by the OS.

[gsvelto]

No specific hardware support is needed to implement a lock. The atomic operations are all accessible from user-space - they are platform dependent though. The problem with locks is that they interact with scheduling and that's where the kernel comes in, that's why you need an OS-specific component too.

[joeldo]

That makes sense, thanks.