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PTHREAD_KEY_CREATE(3)    BSD Library Functions Manual    PTHREAD_KEY_CREATE(3)

NAME
     pthread_key_create -- thread-specific data key creation

SYNOPSIS
     #include <pthread.h>

     int
     pthread_key_create(pthread_key_t *key, void (*destructor)(void *));

DESCRIPTION
     The pthread_key_create() function creates a thread-specific data key that
     is visible 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 perthread
     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 outstanding
     standing non-NULL values, there are still some non-NULL values with asso-ciated associated
     ciated destructors, the implementation stops calling destructors.

RETURN VALUES
     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.

ERRORS
     pthread_key_create() will fail if:

     [EAGAIN]           The system lacked the necessary resources to create
                        another thread-specific data key, or the system-imposed systemimposed
                        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 ALSO
     pthread_getspecific(3), pthread_key_delete(3), pthread_setspecific(3)

STANDARDS
     pthread_key_create() conforms to ISO/IEC 9945-1:1996 (``POSIX.1'').

BSD                              April 4, 1996                             BSD