int pthread_key_delete(pthread_key_t key);
The pthread_key_delete() function shall delete a thread-specific data key previously returned by pthread_key_create(). The thread-specific data values associated with key need not be NULL at the time pthread_key_delete() is called. It is the responsibility of the application to free any application storage or perform any cleanup actions for data structures related to the deleted key or associated thread-specific data in any threads; this cleanup can be done either before or after pthread_key_delete() is called. Any attempt to use key following the call to pthread_key_delete() results in undefined behavior.
The pthread_key_delete() function shall be callable from within destructor functions. No destructor functions shall be invoked by pthread_key_delete(). Any destructor function that may have been associated with key shall no longer be called upon thread exit.
If successful, the pthread_key_delete() function shall return zero; otherwise, an error number shall be returned to indicate the error.
The pthread_key_delete() function may fail if:
The pthread_key_delete() function shall not return an error code of [EINTR].
The following sections are informative.
A thread-specific data key deletion function has been included in order to allow the resources associated with an unused thread-specific data key to be freed. Unused thread-specific data keys can arise, among other scenarios, when a dynamically loaded module that allocated a key is unloaded.
Conforming applications are responsible for performing any cleanup actions needed for data structures associated with the key to be deleted, including data referenced by thread-specific data values. No such cleanup is done by pthread_key_delete(). In particular, destructor functions are not called. There are several reasons for this division of responsibility:
For an application to know that it is safe to delete a key, it has to know that all the threads that might potentially ever use the key do not attempt to use it again. For example, it could know this if all the client threads have called a cleanup procedure declaring that they are through with the module that is being shut down, perhaps by setting a reference count to zero.
pthread_key_create() , the Base Definitions volume of IEEE Std 1003.1-2001, <pthread.h>