pthread_setspecific() returns zero after completing successfully. Any other return value indicates that an error occurred. When any of the following conditions occur, pthread_setspecific() fails and returns the corresponding value.
ENOMEM
Description:Insufficient virtual memory is available.
EINVAL
Description:key is invalid.
pthread_setspecific() does not free its storage when a new binding is set. The existing binding must be freed, otherwise a memory leak can occur.