Chapter 4 Thread-Specific Data

POSIX 1.c Migration Guide

Thread-Specific Data

Version Variations

POSIX.1c incorporates minor revisions to the thread-specific data-related functions versus the POSIX.4a interfaces, as shown in the following table:

Thread-Specific Data Function Changes

POSIX.1c

POSIX.4a

int

pthread_key_create
(pthread_key_t *key,void
(*destructor)void *value))

int

pthread_keycreate
(pthread_key_t *key,void
(*destructor)(void *value))

int

pthread_key_delete
(pthread_key_t key)

No equivalent

int

pthread_setspecific
(pthread_key_t key,const void
*value)

int

pthread_setspecific
(pthread_key_t key,void *value)

void *

pthread_getspecific
(pthread_key_t key)

int

pthread_getspecific
(pthread_key_t key,void **value)

POSIX.4a does not provide a facility for deleting a thread-specific data key, which is provided in POSIX.1c by the pthread_key_delete() function.

Note: The pthread_key_delete() function in LynxOS is currently a no-op. Therefore, repeatedly deleting and recreating keys in a thread may cause the
per-thread key limit to be exceeded.

In POSIX.1c, the pthread_getspecific() function cannot return an error. If no thread-specific data value is associated with the specified key, pthread_getspecific() returns NULL.

Note: This also means that setting the value associated with a key to NULL using pthread_setspecific() results in an ambiguous return value from a subsequent call to pthread_getspecific() for that key.

Thread-Specific Data Function Changes
POSIX.1c	POSIX.4a
int pthread_key_create (pthread_key_t key,void (destructor)void *value))	int pthread_keycreate (pthread_key_t key,void (destructor)(void *value))
int pthread_key_delete (pthread_key_t key)	No equivalent
int pthread_setspecific (pthread_key_t key,const void *value)	int pthread_setspecific (pthread_key_t key,void *value)
void * pthread_getspecific (pthread_key_t key)	int pthread_getspecific (pthread_key_t key,void **value)

Note: The pthread_key_delete() function in LynxOS is currently a no-op. Therefore, repeatedly deleting and recreating keys in a thread may cause the per-thread key limit to be exceeded.

Note: This also means that setting the value associated with a key to NULL using pthread_setspecific() results in an ambiguous return value from a subsequent call to pthread_getspecific() for that key.

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