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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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