pthread_key_delete(3p) — Linux manual page



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




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

       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.



SEE ALSO         top


       The Base Definitions volume of POSIX.1‐2017, pthread.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 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 .

       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 .

IEEE/The Open Group               2017            PTHREAD_KEY_DELETE(3P)

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