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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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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.1‐2017, pthread.h(0p)
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 http://www.opengroup.org/unix/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 2017 PTHREAD_KEY_DELETE(3P)
Pages that refer to this page: pthread.h(0p), pthread_key_create(3p)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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