1PTHREAD_KEY_DELETE(3P) POSIX Programmer's Manual PTHREAD_KEY_DELETE(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
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12 pthread_key_delete — thread-specific data key deletion
13
15 #include <pthread.h>
16 int pthread_key_delete(pthread_key_t key);
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20 The pthread_key_delete() function shall delete a thread-specific data
21 key previously returned by pthread_key_create(). The thread-specific
22 data values associated with key need not be NULL at the time
23 pthread_key_delete() is called. It is the responsibility of the appli‐
24 cation to free any application storage or perform any cleanup actions
25 for data structures related to the deleted key or associated thread-
26 specific data in any threads; this cleanup can be done either before or
27 after pthread_key_delete() is called. Any attempt to use key following
28 the call to pthread_key_delete() results in undefined behavior.
29 The pthread_key_delete() function shall be callable from within
31 destructor functions. No destructor functions shall be invoked by
32 pthread_key_delete(). Any destructor function that may have been asso‐
33 ciated with key shall no longer be called upon thread exit.
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36 If successful, the pthread_key_delete() function shall return zero;
37 otherwise, an error number shall be returned to indicate the error.
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40 The pthread_key_delete() function shall not return an error code of
41 [EINTR].
42 The following sections are informative.
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46 None.
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49 None.
50
52 A thread-specific data key deletion function has been included in order
53 to allow the resources associated with an unused thread-specific data
54 key to be freed. Unused thread-specific data keys can arise, among
55 other scenarios, when a dynamically loaded module that allocated a key
56 is unloaded.
57 Conforming applications are responsible for performing any cleanup
59 actions needed for data structures associated with the key to be
60 deleted, including data referenced by thread-specific data values. No
61 such cleanup is done by pthread_key_delete(). In particular, destruc‐
62 tor functions are not called. There are several reasons for this divi‐
63 sion of responsibility:
64 1. The associated destructor functions used to free thread-specific
66 data at thread exit time are only guaranteed to work correctly when
67 called in the thread that allocated the thread-specific data.
68 (Destructors themselves may utilize thread-specific data.) Thus,
69 they cannot be used to free thread-specific data in other threads
70 at key deletion time. Attempting to have them called by other
71 threads at key deletion time would require other threads to be
72 asynchronously interrupted. But since interrupted threads could be
73 in an arbitrary state, including holding locks necessary for the
74 destructor to run, this approach would fail. In general, there is
75 no safe mechanism whereby an implementation could free thread-spe‐
76 cific data at key deletion time.
77 2. Even if there were a means of safely freeing thread-specific data
79 associated with keys to be deleted, doing so would require that
80 implementations be able to enumerate the threads with non-NULL data
81 and potentially keep them from creating more thread-specific data
82 while the key deletion is occurring. This special case could cause
83 extra synchronization in the normal case, which would otherwise be
84 unnecessary.
85 For an application to know that it is safe to delete a key, it has to
87 know that all the threads that might potentially ever use the key do
88 not attempt to use it again. For example, it could know this if all the
89 client threads have called a cleanup procedure declaring that they are
90 through with the module that is being shut down, perhaps by setting a
91 reference count to zero.
92 If an implementation detects that the value specified by the key argu‐
94 ment to pthread_key_delete() does not refer to a a key value obtained
95 from pthread_key_create() or refers to a key that has been deleted with
96 pthread_key_delete(), it is recommended that the function should fail
97 and report an [EINVAL] error.
98
100 None.
101
103 pthread_key_create()
104 The Base Definitions volume of POSIX.1‐2017, <pthread.h>
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108 Portions of this text are reprinted and reproduced in electronic form
109 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
110 table Operating System Interface (POSIX), The Open Group Base Specifi‐
111 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
112 Electrical and Electronics Engineers, Inc and The Open Group. In the
113 event of any discrepancy between this version and the original IEEE and
114 The Open Group Standard, the original IEEE and The Open Group Standard
115 is the referee document. The original Standard can be obtained online
116 at http://www.opengroup.org/unix/online.html .
117 Any typographical or formatting errors that appear in this page are
119 most likely to have been introduced during the conversion of the source
120 files to man page format. To report such errors, see https://www.ker‐
121 nel.org/doc/man-pages/reporting_bugs.html .
122IEEE/The Open Group 2017 PTHREAD_KEY_DELETE(3P)