Lock (lock primitive) Definition/Meaning:
An indivisible operation that allows a process to ensure that it alone has access to a particular resource. On a single-processor system
the indivisible nature of the operation can be guaranteed by turning off
interrupts during the action, ensuring that no process switch can occur. On a
multiprocessing system it is essential to have available a test-and-set
instruction that, in a single uninterruptible sequence, can test whether a
register's contents are zero, and if they are will make the contents nonzero.
The same effect can be achieved by an exchange instruction. See also unlock,