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.
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
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
Both functions may be implemented as macros.
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.
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.
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.
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
IEEE/The Open Group 2013 PTHREAD_GETSPECIFIC(3P)