NAME
pthread_getspecific
pthread_setspecific —
thread-specific data management
SYNOPSIS
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(3). 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(3) or after key has
been deleted with pthread_key_delete(3) 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 non-NULL 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].
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(3), the Base Definitions volume of IEEE Std 1003.1-2001 (“POSIX.1”), <pthread.h>
CHANGE HISTORY
First released in Issue 5. Included for alignment with the POSIX Threads Extension.
Issue 6
The pthread_getspecific () and
pthread_setspecific () functions are marked as part
of the Threads option.
IEEE PASC Interpretation 1003.1c #3 (Part 6) is applied, updating the DESCRIPTION.
IEEE Std 1003.1-2001 (“POSIX.1”)/Cor 2-2004, item XSH/TC2/D6/96 is applied, updating the ERRORS section so that the [ENOMEM] error case is changed from ``to associate the value with the key'' to ``to associate the non-NULL value with the key''.
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