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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 (consult 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  man-
       agement
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 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.
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 non-NULL value  with
              the key.
       The  pthread_setspecific()  function  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.
       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.
FUTURE DIRECTIONS
       None.
SEE ALSO
       pthread_key_create()
       The Base Definitions volume of POSIX.1-2008, <pthread.h>
COPYRIGHT
       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)