pthread_key_create(3C)					   Standard C Library Functions 				    pthread_key_create(3C)

NAME

       pthread_key_create, pthread_key_create_once_np - create thread-specific data key

SYNOPSIS

       cc -mt [ flag... ] file... -lpthread [ library... ]
       #include <pthread.h>

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

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

DESCRIPTION

       The  pthread_key_create()  function  creates  a	thread-specific  data  key  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 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 associ-
       ated 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 that key, the function pointed to is called with the current associated value as its
       sole argument. Destructors can be called in any order.

       If, after all the destructors have been	called for all keys with non-NULL values,  there are still some keys  with  non-NULL  values,  the
       process will be repeated. If, after at least  PTHREAD_DESTRUCTOR_ITERATIONS iterations of destructor calls for outstanding non-NULL values,
       there are still some keys with non-NULL values, the process is continued, even though this might result in an infinite loop.

       An exiting thread runs with all signals blocked. All thread termination functions, including thread-specific data destructor functions, are
       called with all signals blocked.

       The pthread_key_create_once_np() function is identical to the pthread_key_create() function except that the key referred to by *key must be
       statically initialized with the value PTHREAD_ONCE_KEY_NP before calling pthread_key_create_once_np(), and the key is created exactly once.
       This  function  call  is  equivalent to using pthread_once(3C) to call a onetime initialization function that calls pthread_key_create() to
       create the data key.

RETURN VALUES

       If successful, the pthread_key_create() and pthread_key_create_once_np() functions store the newly created key value at *key and return	0.
       Otherwise, an error number is returned to indicate the error.

ERRORS

       The  pthread_key_create() and pthread_key_create_once_np() functions 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 has been exceeded.

       ENOMEM	 Insufficient memory exists to create the key.

       The pthread_key_create() and pthread_key_create_once_np() functions will not return an error value of EINTR.

EXAMPLES

       Example 1 Call thread-specific data in the function from more than one thread without special initialization.

       In the following example, the thread-specific data in the function can be called from more than one thread without special  initialization.
       For each argument passed to the executable, a thread is created and privately bound to the string-value of that argument.

	 /* cc -mt thisfile.c */

	 #include <stdio.h>
	 #include <stdlib.h>
	 #include <string.h>
	 #include <pthread.h>

	 static void *thread_function(void *);
	 static void show_tsd(void);
	 static void cleanup(void*);

	 #define MAX_THREADS 20

	 static pthread_key_t tsd_key = PTHREAD_ONCE_KEY_NP;

	 int
	 main(int argc, char *argv[])
	 {
	      pthread_t tid[MAX_THREADS];
	      int num_threads;
	      int i;

	      if ((num_threads = argc - 1) > MAX_THREADS)
		   num_threads = MAX_THREADS;
	      for (i = 0; i < num_threads; i++)
		   pthread_create(&tid[i], NULL, thread_function, argv[i+1]);
	      for (i = 0; i < num_threads; i++)
		   pthread_join(tid[i], NULL);
	      return(0);
	 }

	 static void *
	 thread_function(void *arg)
	 {
	      char *data;

	      pthread_key_create_once_np(&tsd_key, cleanup);
	      data = malloc(strlen(arg) + 1);
	      strcpy(data, arg);
	      pthread_setspecific(tsd_key, data);
	      show_tsd();
	      return (NULL);
	 }

	 static void
	 show_tsd()
	 {
	      void *tsd = pthread_getspecific(tsd_key);

	      printf("tsd for %d = %s
", pthread_self(), (char *)tsd);
	 }

	 /* application-specific clean-up function */
	 static void
	 cleanup(void *tsd)
	 {
	      printf("freeing tsd for %d = %s
", pthread_self(), (char *)tsd);
	      free(tsd);
	 }

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Committed.		   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+
       |Standard		     |See below.		   |
       +-----------------------------+-----------------------------+

       For pthread_key_create(), see standards(5).

SEE ALSO

       pthread_once(3C), pthread_getspecific(3C), pthread_setspecific(3C), pthread_key_delete(3C), attributes(5), standards(5)

SunOS 5.11							    2 Nov 2007						    pthread_key_create(3C)