The
pthread_getspecific() function returns the value currently bound to the specified
key on behalf of the calling thread. Conversely, the
pthread_setspecific() function associates a thread-specific value with a
key obtained via a previous call to
pthread_key_create(3). Different threads have different values bound to each key. These values are typically pointers to blocks of dynamically allocated memory that have been reserved for use by the calling thread.
Undefined behavior may follow if either function is called with a
key value not obtained from
pthread_key_create(3), or if the call is made after
key has been deleted with
pthread_key_delete(3). It is possible to call either function from a thread-specific data destructor function. Note however that this is not well defined for the
pthread_setspecific() function; lost storage or infinite loops may occur.