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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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PTHREAD_GETSPECIFIC(3P) POSIX Programmer's Manual PTHREAD_GETSPECIFIC(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.
pthread_getspecific, pthread_setspecific — thread-specific data
management
#include <pthread.h>
void *pthread_getspecific(pthread_key_t key);
int pthread_setspecific(pthread_key_t key, const void *value);
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.
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 [EINTR].
The following sections are informative.
None.
None.
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.
None.
pthread_key_create(3p)
The Base Definitions volume of POSIX.1‐2017, pthread.h(0p)
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(3P)
Pages that refer to this page: pthread.h(0p), pthread_key_create(3p), pthread_setspecific(3p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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