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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 threadspecific
     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 call-ing calling
     ing 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.  If a key value has a non-NULL
     destructor function pointer, and the thread has a non-NULL value associated with the key at the time of
     thread exit, then the key value is set to NULL and the destructor function is called with the previous
     key value as its argument.  The order of destructor calls at thread exit is unspecified.

     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 outstanding non-NULL
     values, there are still some non-NULL values with associated 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 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