pthread_getspecific manpage

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

       pthread_getspecific, pthread_setspecific -- thread-specific  data  man-

       #include <pthread.h>

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

       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 val-
       ues  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_getspe-
       cific() 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_setspe-
       cific()	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.

       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.

       No errors are returned from pthread_getspecific().

       The pthread_setspecific() function shall fail if:

       ENOMEM Insufficient memory exists to associate the non-NULL value  with
	      the key.

       The  pthread_setspecific()  function  shall not return an error code of

       The following sections are informative.



       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.

       If  an implementation detects that the value specified by the key argu-
       ment to pthread_setspecific() does not refer to a a key value  obtained
       from pthread_key_create() or refers to a key that has been deleted with
       pthread_key_delete(), it is recommended that the function  should  fail
       and report an [EINVAL] error.



       The Base Definitions volume of POSIX.1-2008, <pthread.h>

       Portions	 of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       --  Portable  Operating	System	Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
       cal  and	 Electronics  Engineers,  Inc  and  The	 Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum	 1  applied.)  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.unix.org/online.html .

       Any typographical or formatting errors that appear  in  this  page  are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors,	 see  https://www.ker-
       nel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group		     2013	       PTHREAD_GETSPECIFIC(3P)