pthread_getspecific(3p) — Linux manual page



PROLOG         top

       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         top

       pthread_getspecific, pthread_setspecific — thread-specific data

SYNOPSIS         top

       #include <pthread.h>

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

DESCRIPTION         top

       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         top

       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         top

       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.

EXAMPLES         top




RATIONALE         top

       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.



SEE ALSO         top


       The Base Definitions volume of POSIX.1‐2008, pthread.h(0p)

COPYRIGHT         top

       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 .

       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 .

IEEE/The Open Group                 2013             PTHREAD_GETSPECIFIC(3P)

Pages that refer to this page: pthread.h(0p)pthread_key_create(3p)pthread_setspecific(3p)