PTHREAD_GETSPECIFIC(3P)                             POSIX Programmer's Manual                            PTHREAD_GETSPECIFIC(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

NAME
       pthread_getspecific, pthread_setspecific - thread-specific data management

SYNOPSIS
       #include <pthread.h>

       void *pthread_getspecific(pthread_key_t key);
       int pthread_setspecific(pthread_key_t key, const void *value);


DESCRIPTION
       The  pthread_getspecific()  function shall return the value currently bound to the specified key on behalf of the calling
       thread.

       The pthread_setspecific() function shall associate a thread-specific value with a key obtained via  a  previous  call  to
       pthread_key_create(). Different threads may bind different values to the same key. These values are typically pointers to
       blocks of dynamically allocated memory that have been reserved for use by the calling thread.

       The effect of calling pthread_getspecific() or pthread_setspecific() with a key value not obtained from  pthread_key_cre-
       ate() or after key has been deleted with pthread_key_delete() is undefined.

       Both  pthread_getspecific()  and  pthread_setspecific()  may be called from a thread-specific data destructor function. A
       call to pthread_getspecific() for the thread-specific data key being destroyed shall return the value  NULL,  unless  the
       value  is  changed (after the destructor starts) by a call to pthread_setspecific(). Calling pthread_setspecific() from a
       thread-specific data destructor routine may result either in lost storage (after at  least  PTHREAD_DESTRUCTOR_ITERATIONS
       attempts at destruction) or in an infinite loop.

       Both functions may be implemented as macros.

RETURN VALUE
       The  pthread_getspecific()  function  shall  return  the  thread-specific data value associated with the given key. If no
       thread-specific data value is associated with key, then the value NULL shall be returned.

       If successful, the pthread_setspecific() function shall return zero; otherwise, an error  number  shall  be  returned  to
       indicate the error.

ERRORS
       No errors are returned from pthread_getspecific().

       The pthread_setspecific() function shall fail if:

       ENOMEM Insufficient memory exists to associate the value with the key.


       The pthread_setspecific() function may fail if:

       EINVAL The key value is invalid.


       These functions shall not return an error code of [EINTR].

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       None.

RATIONALE
       Performance and ease-of-use of pthread_getspecific() are critical for functions that rely on maintaining state in thread-
       specific data. Since no errors are required to be detected by it, and since the only error that could be detected is  the
       use  of  an invalid key, the function to pthread_getspecific() has been designed to favor speed and simplicity over error
       reporting.

FUTURE DIRECTIONS
       None.

SEE ALSO
       pthread_key_create(), the Base Definitions volume of IEEE Std 1003.1-2001, <pthread.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003  Edition,  Standard  for
       Information  Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copy-
       right (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any
       discrepancy  between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group
       Standard  is  the  referee   document.   The   original   Standard   can   be   obtained   online   at   http://www.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                       PTHREAD_GETSPECIFIC(3P)