This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       None.

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for  Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       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 .

IEEE/The Open Group                                   2017                           PTHREAD_GETSPECIFIC(3POSIX)

       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.

       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].

       Thefollowingsectionsareinformative.

       None.

       None.

       pthread_getspecific, pthread_setspecific — thread-specific data management

       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.

       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.

       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.

pthread_key_create()

       The Base Definitions volume of POSIX.1‐2017, <pthread.h>

       #include <pthread.h>

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