Mutual exclusion implementations
Mutual exclusion is the principle which underlies thread-safe access of data within a multithreaded application. One can implement this both in hardware and software. The mutual exclusion (mutex) is the most elementary form of this functionality in most implementations.
Hardware
The simplest hardware-based implementation on a uniprocessor (single processor core), non-SMT system is to disable interrupts, and thus, prevent the task from being changed. More commonly, a so-called busy-wait principle is employed. This is the basic principle behind a mutex--due to how the processor fetches data, only one task can obtain and read/write an atomic value in the shared memory, meaning, a variable sized the same (or smaller) as the CPU's registers. This is further detailed in Chapter 8, Atomic Operations - Working with the Hardware.
When our code tries to lock a mutex, what this does is read the value of such an atomic section of memory, and try to set it to its locked...
