The function int pthread_spin_init(pthread_spinlock_t *lock, int pshared); shall allocate any resources required to use the spin lock referenced by lock and initialize the lock to an unlocked state. If the Thread Process-Shared Synchronization option is supported and the value of pshared is PTHREAD_PROCESS_SHARED, the implementation shall permit the spin lock to be operated upon by any thread that has access to the memory where the spin lock is allocated, even if it is allocated in memory that is shared by multiple processes. If the Thread Process-Shared Synchronization option is supported and the value of pshared is PTHREAD_PROCESS_PRIVATE, or if the option is not supported, the spin lock shall only be operated upon by threads created within the same process as the thread that initialized the spinlock. If threads of differing processes attempt to operate on such a spin lock, the behavior is undefined. Upon successful completion, these functions shall return zero; otherwise, an error number shall be returned to indicate the error. This function may fail if: -[EBUSY] The implementation has detected an attempt to initialize or destroy a spin lock while it is in use (for example, while being used in a pthread_spin_lock( ) by another thread. -[EINVAL] The value specified by lock is invalid. It shall fail if: -[EAGAIN] The system lacks the necessary resources to initialize another spin lock. -[ENOMEM] Insufficient memory exists to initialize the lock. These functions shall not return an error code of EINTR.