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PTHREAD_KEY_DELETE(3P) POSIX Programmer's Manual PTHREAD_KEY_DELETE(3P)
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.
pthread_key_delete — thread-specific data key deletion
#include <pthread.h>
int pthread_key_delete(pthread_key_t key);
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.
If successful, the pthread_key_delete() function shall return zero;
otherwise, an error number shall be returned to indicate the error.
The pthread_key_delete() function shall not return an error code of
[EINTR].
The following sections are informative.
None.
None.
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.
None.
pthread_key_create(3p)
The Base Definitions volume of POSIX.1‐2008, pthread.h(0p)
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)