PTHREAD_GETSPECIFIC(P) POSIX Programmer's Manual PTHREAD_GETSPECIFIC(P)
pthread_getspecific, pthread_setspecific - thread-specific data management
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 allo-
cated 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()
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 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.
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
pthread_key_create() , the Base Definitions volume of IEEE Std 1003.1-2001, <pthread.h>
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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 PTHREAD_GETSPECIFIC(P)