Indeed.
Just a reminder to everyone: your pthreads_mutex_lock() and pthreads_mutex_unlock() functions already contain the appropriate compiler / cache memory barriers in the correct locations.
This "Memory Model" discussion is only for people who want to build faster systems: for people searching for a "better spinlock", or for writing lock-free algorithms / lock-free data structures.
This is the stuff of cutting edge research right now: its a niche subject. Your typical programmer _SHOULD_ just stick a typical pthread_mutex_t onto an otherwise single-threaded data-structure and call it. Locks work. They're not "the best", but "the best" is constantly being researched / developed right now. I'm pretty sure that any new lockfree data-structure with decent performance is pretty much an instant PH.D thesis material.
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Anyway, the reason why "single-threaded data-structure behind a mutex" works is because your data-structure still keeps all of its performance benefits (from sticking to L1 cache, or letting the compiler "manually cache" data to registers when appropriate), and then you only lose performance when associated with the lock() or unlock() calls (which will innately have memory barriers to publish the results)
That's 2 memory barriers (one barrier for lock() and one barrier for unlock()). The thing about lock-free algorithms is that they __might__ get you down to __1__ memory barrier per operation if you're a really, really good programmer. But its not exactly easy. (Or: they might still have 2 memory barriers but the lockfree aspect of "always forward progress" and/or deadlock free might be easier to prove)
Writing a low-performance but otherwise correct lock free algorithm isn't actually that hard. Writing a lock free algorithm that beats your typical mutex + data-structure however, is devilishly hard.
