The function void *pthread_setspecific(pthread_key_t key) shall acssociate a thread-specific value with a key obtained via a previouse call to pthread_key_create. Different threads may bind different values to the same key. Calling pthread_setspecific with a key value not obtiained from pthread_key_create of after the key has been deleted with pthread_key_delete is undefined. pthread_setspecific may be called from a thread-specific data destructor function. A call to pthread_getspecific() from a thread-specific data destructor routine may result either in lost storage or in an infinite loop. It returns 0 upon success, and an error number otherwise: Shall fail if: [ENOMEM] - Insufficient memory exists to associate the value with the key May fail if: [EINVAL] - The key value is invalid