Section: POSIX Programmer's Manual (3P)
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.
--- thread-specific data management
void *pthread_getspecific(pthread_key_t key);
int pthread_setspecific(pthread_key_t key, const void *value);
function shall return the value currently bound to the specified
on behalf of the calling thread.
function shall associate a thread-specific
obtained via a previous call to
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
value not obtained from
has been deleted with
may be called from a thread-specific data destructor function. A call
for the thread-specific data key being destroyed shall return the value
NULL, unless the value is changed (after the destructor starts) by a
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.
function shall return the thread-specific data value associated
with the given
If no thread-specific data value is associated with
then the value NULL shall be returned.
If successful, the
function shall return zero; otherwise, an error number shall be
returned to indicate the error.
No errors are returned from
function shall fail if:
Insufficient memory exists to associate the non-NULL value with the key.
function shall not return an error code of
The following sections are informative.
Performance and ease-of-use of
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
has been designed to favor speed and simplicity over error reporting.
If an implementation detects that the value specified by the
does not refer to a a key value obtained from
or refers to a key that has been deleted with
it is recommended that the function should fail and report an
The Base Definitions volume of POSIX.1-2008,
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
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