PTHREAD_KEY_CREATE(3) BSD Library Functions Manual PTHREAD_KEY_CREATE(3)NAMEpthread_key_create — thread-specific data key creation
POSIX Threads Library (libpthread, -lpthread)
pthread_key_create(pthread_key_t *key, void (*destructor)(void *));
The pthread_key_create() function creates a thread-specific data key vis‐
ible to all threads in the process. Key values provided by
pthread_key_create() are opaque objects used to locate thread-specific
data. Although the same key value may be used by different threads, the
values bound to the key by pthread_setspecific() are maintained on a per-
thread basis and persist for the life of the calling thread.
Upon key creation, the value NULL is associated with the new key in all
active threads. Upon thread creation, the value NULL is associated with
all defined keys in the new thread.
An optional destructor function may be associated with each key value.
At thread exit, if a key value has a non-NULL destructor pointer, and the
thread has a non-NULL value associated with the key, the function pointed
to is called with the current associated value as its sole argument. The
order of destructor calls is unspecified if more than one destructor
exists for a thread when it exits.
If, after all the destructors have been called for all non-NULL values
with associated destructors, there are still some non-NULL values with
associated destructors, then the process is repeated. If, after at least
[PTHREAD_DESTRUCTOR_ITERATIONS] iterations of destructor calls for out‐
standing non-NULL values, there are still some non-NULL values with asso‐
ciated destructors, the implementation stops calling destructors.
If successful, the pthread_key_create() function will store the newly
created key value at the location specified by key and returns zero.
Otherwise an error number will be returned to indicate the error.
The pthread_key_create() function will fail if:
[EAGAIN] The system lacked the necessary resources to create
another thread-specific data key, or the system-
imposed limit on the total number of keys per process
[PTHREAD_KEYS_MAX] would be exceeded.
[ENOMEM] Insufficient memory exists to create the key.
SEE ALSOpthread_getspecific(3), pthread_key_delete(3), pthread_setspecific(3)STANDARDS
The pthread_key_create() function conforms to ISO/IEC 9945-1:1996
BSD April 4, 1996 BSD