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 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 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  argument  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  Electrical  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.kernel.org/doc/man-pages/reporting_bugs.html .