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 .