Posix Eşzamanlılık Yapıları - Spinlock

Giriş
Bu yapıyı user space içinde kullanmak iyi bir fikir olmayabilir. Açıklaması şöyle.

Spinlocks are often considered a wrong tool in user-space because there is no way to disable thread preemption while the spinlock is held (unlike in kernel).

So that a thread can acquire a spinlock and then get preempted, causing all other threads trying to acquire the spinlock to spin unnecessarily (and if those threads are of higher priority that may cause a deadlock (threads waiting for I/O may get a priority boost on wake up)).

This reasoning also applies to all lockless data structures, unless the data structure is truly wait-free (there aren't many practically useful ones, apart from boost::spsc_queue).

Kernel (çekilrdekte) durum farklı. Açıklaması şöyle.

In kernel, a thread that has locked a spinlock cannot be preempted or interrupted before it releases the spinlock. And that is why spinlocks are appropriate there

Linux'ta SpinLock için Iteration Sayabilen Bir Yapı Var
Açıklaması şöyle.

On Linux, there is adaptive mutex PTHREAD_MUTEX_ADAPTIVE_NP, which spins for a limited number of iterations before blocking in the kernel (similar to InitializeCriticalSectionAndSpinCount). However, that mutex cannot be used through std::mutex interface because there is no option to customise non-portable pthread_mutexattr_t before initialising pthread_mutex_t.

One can neither enable process-sharing, robustness, error-checking or priority-inversion prevention through std::mutex interface. In practice, people write their own wrappers of pthread_mutex_t which allows to set desirable mutex attributes; along with a corresponding wrapper for condition variables. Standard locks like std::unique_lock and std::lock_guard can be reused.