thread-specific data key creation
() function creates a
thread-specific data key visible to all threads in the process. Key values
() 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
() 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
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.
If successful, the
function will store the newly created key value at the location specified by
and returns zero. Otherwise an error
number will be returned to indicate the error.
() will fail if:
- 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.
- Insufficient memory exists to create the key.
() conforms to