Why is there no std:: equivalent to pthread_spinlock_t like there is for pthread_mutex_t & std::mutex?

I've used pthreads a fair bit for concurrent programs, mainly utilising spinlocks, mutexes, and condition variables.

I started looking into multithreading using std::thread and using std::mutex, and I noticed that there doesn't seem to be an equivalent to spinlock in pthreads.

Anyone know why this is?