Comment by adwn

> […] but don't cover the use cases of all users.

No single concurrency primitive covers all use cases. I was addressing your misconceptions about mutex performance and overhead, not whether mutexes are the best solution to your particular problem.

> […] it has no way of getting notified when the mutex gets unblocked […] The OS (lets assume Linux) wont wake it up the thread until the next scheduler tick, and its under no obligation to do so even then (and has no idea it should).

You've misunderstood the parking_lot implementation. When thread B tries to lock a mutex that's currently locked by thread A, then, after spinning a few cycles, thread B "parks" itself, i.e., it asks the kernel to remove it from the Runnable task queue. On Linux, this is done using the futex syscall. When thread A unlocks the mutex, it detects that another thread is waiting on that mutex. Thread A takes one thread from the queue of waiting threads and "unparks" it, i.e., it asks the kernel to move it into the Runnable task queue. The kernel is notified immediately, and if there's a free CPU core available, will tend to dispatch the thread to that core. On a non-realtime OS, there's no guarantee how long it takes for an unblocked thread to be scheduled again, but that's the case for all concurrency primitives.