"What locks it" can include "owned by different threads". That's a lock at a higher level, really.
"Lock free" data structures are tied very closely to the data being locked, and depend heavily on certain CPU operations being atomic. This is more of an issue with ARM than with x86, because ARM needs more fence instructions. Really, "lock free" programming is just locking critical sections with lower level hardware primitives.
The opposite extreme is POSIX locks. Locks are the OS's problem, and nothing in the code says what's covered by the lock. That was once standard practice and is now recognized as being bad.
"Lock free" data structures are tied very closely to the data being locked, and depend heavily on certain CPU operations being atomic. This is more of an issue with ARM than with x86, because ARM needs more fence instructions. Really, "lock free" programming is just locking critical sections with lower level hardware primitives.
The opposite extreme is POSIX locks. Locks are the OS's problem, and nothing in the code says what's covered by the lock. That was once standard practice and is now recognized as being bad.