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_create() 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, Copyright (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.opengroup.org/unix/online.html .