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PTHREAD_GETSPECIFIC
Section: POSIX Programmer's Manual (3P)
Updated: 2003
Index
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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 value with the key.
The pthread_setspecific() function may fail if:
- EINVAL
-
The key value is invalid.
These functions 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.
FUTURE DIRECTIONS
None.
SEE ALSO
pthread_key_create(), the Base Definitions volume of
IEEE Std 1003.1-2001, <pthread.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .
Index
- PROLOG
-
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- EXAMPLES
-
- APPLICATION USAGE
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
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