PTHREAD_GETSPECIFIC(P) POSIX Programmer's Manual PTHREAD_GETSPECIFIC(P)NAME
pthread_getspecific, pthread_setspecific - thread-specific data manage‐
ment
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 val‐
ues 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_getspe‐
cific() 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_setspe‐
cific() 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 ALSOpthread_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 .
IEEE/The Open Group 2003 PTHREAD_GETSPECIFIC(P)
