PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

PTHREAD_KEY_DELETE(3P)    POSIX Programmer's Manual   PTHREAD_KEY_DELETE(3P)

PROLOG         top

       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         top

       pthread_key_delete — thread-specific data key deletion

SYNOPSIS         top

       #include <pthread.h>

       int pthread_key_delete(pthread_key_t key);

DESCRIPTION         top

       The pthread_key_delete() function shall delete a thread-specific data
       key previously returned by pthread_key_create().  The thread-specific
       data values associated with key need not be NULL at the time
       pthread_key_delete() is called. It is the responsibility of the
       application to free any application storage or perform any cleanup
       actions for data structures related to the deleted key or associated
       thread-specific data in any threads; this cleanup can be done either
       before or after pthread_key_delete() is called. Any attempt to use
       key following the call to pthread_key_delete() results in undefined
       behavior.

       The pthread_key_delete() function shall be callable from within
       destructor functions. No destructor functions shall be invoked by
       pthread_key_delete().  Any destructor function that may have been
       associated with key shall no longer be called upon thread exit.

RETURN VALUE         top

       If successful, the pthread_key_delete() function shall return zero;
       otherwise, an error number shall be returned to indicate the error.

ERRORS         top

       The pthread_key_delete() function shall not return an error code of
       [EINTR].

       The following sections are informative.

EXAMPLES         top

       None.

APPLICATION USAGE         top

       None.

RATIONALE         top

       A thread-specific data key deletion function has been included in
       order to allow the resources associated with an unused thread-
       specific data key to be freed. Unused thread-specific data keys can
       arise, among other scenarios, when a dynamically loaded module that
       allocated a key is unloaded.

       Conforming applications are responsible for performing any cleanup
       actions needed for data structures associated with the key to be
       deleted, including data referenced by thread-specific data values. No
       such cleanup is done by pthread_key_delete().  In particular,
       destructor functions are not called. There are several reasons for
       this division of responsibility:

        1. The associated destructor functions used to free thread-specific
           data at thread exit time are only guaranteed to work correctly
           when called in the thread that allocated the thread-specific
           data. (Destructors themselves may utilize thread-specific data.)
           Thus, they cannot be used to free thread-specific data in other
           threads at key deletion time.  Attempting to have them called by
           other threads at key deletion time would require other threads to
           be asynchronously interrupted. But since interrupted threads
           could be in an arbitrary state, including holding locks necessary
           for the destructor to run, this approach would fail. In general,
           there is no safe mechanism whereby an implementation could free
           thread-specific data at key deletion time.

        2. Even if there were a means of safely freeing thread-specific data
           associated with keys to be deleted, doing so would require that
           implementations be able to enumerate the threads with non-NULL
           data and potentially keep them from creating more thread-specific
           data while the key deletion is occurring. This special case could
           cause extra synchronization in the normal case, which would
           otherwise be unnecessary.

       For an application to know that it is safe to delete a key, it has to
       know that all the threads that might potentially ever use the key do
       not attempt to use it again. For example, it could know this if all
       the client threads have called a cleanup procedure declaring that
       they are through with the module that is being shut down, perhaps by
       setting a reference count to zero.

       If an implementation detects that the value specified by the key
       argument to pthread_key_delete() does not refer to a a key value
       obtained from pthread_key_create() or refers to a key that has been
       deleted with pthread_key_delete(), it is recommended that the
       function should fail and report an [EINVAL] error.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       pthread_key_create(3p)

       The Base Definitions volume of POSIX.1‐2008, pthread.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the
       source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013              PTHREAD_KEY_DELETE(3P)

Pages that refer to this page: pthread.h(0p)pthread_key_create(3p)