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.
10
12 pthread_key_delete - thread-specific data key deletion
13
15 #include <pthread.h>
16 int pthread_key_delete(pthread_key_t key);
18
21 The pthread_key_delete() function shall delete a thread-specific data
22 key previously returned by pthread_key_create(). The thread-specific
23 data values associated with key need not be NULL at the time
24 pthread_key_delete() is called. It is the responsibility of the appli‐
25 cation to free any application storage or perform any cleanup actions
26 for data structures related to the deleted key or associated thread-
27 specific data in any threads; this cleanup can be done either before or
28 after pthread_key_delete() is called. Any attempt to use key following
29 the call to pthread_key_delete() results in undefined behavior.
30 The pthread_key_delete() function shall be callable from within
32 destructor functions. No destructor functions shall be invoked by
33 pthread_key_delete(). Any destructor function that may have been asso‐
34 ciated with key shall no longer be called upon thread exit.
35
37 If successful, the pthread_key_delete() function shall return zero;
38 otherwise, an error number shall be returned to indicate the error.
39
41 The pthread_key_delete() function may fail if:
42 EINVAL The key value is invalid.
44 The pthread_key_delete() function shall not return an error code of
47 [EINTR].
48 The following sections are informative.
50
52 None.
53
55 None.
56
58 A thread-specific data key deletion function has been included in order
59 to allow the resources associated with an unused thread-specific data
60 key to be freed. Unused thread-specific data keys can arise, among
61 other scenarios, when a dynamically loaded module that allocated a key
62 is unloaded.
63 Conforming applications are responsible for performing any cleanup
65 actions needed for data structures associated with the key to be
66 deleted, including data referenced by thread-specific data values. No
67 such cleanup is done by pthread_key_delete(). In particular, destructor
68 functions are not called. There are several reasons for this division
69 of responsibility:
70 1. The associated destructor functions used to free thread-specific
72 data at thread exit time are only guaranteed to work correctly when
73 called in the thread that allocated the thread-specific data.
74 (Destructors themselves may utilize thread-specific data.) Thus,
75 they cannot be used to free thread-specific data in other threads
76 at key deletion time. Attempting to have them called by other
77 threads at key deletion time would require other threads to be
78 asynchronously interrupted. But since interrupted threads could be
79 in an arbitrary state, including holding locks necessary for the
80 destructor to run, this approach would fail. In general, there is
81 no safe mechanism whereby an implementation could free thread-spe‐
82 cific data at key deletion time.
83 2. Even if there were a means of safely freeing thread-specific data
85 associated with keys to be deleted, doing so would require that
86 implementations be able to enumerate the threads with non-NULL data
87 and potentially keep them from creating more thread-specific data
88 while the key deletion is occurring. This special case could cause
89 extra synchronization in the normal case, which would otherwise be
90 unnecessary.
91 For an application to know that it is safe to delete a key, it has to
93 know that all the threads that might potentially ever use the key do
94 not attempt to use it again. For example, it could know this if all the
95 client threads have called a cleanup procedure declaring that they are
96 through with the module that is being shut down, perhaps by setting a
97 reference count to zero.
98
100 None.
101
103 pthread_key_create(), the Base Definitions volume of
104 IEEE Std 1003.1-2001, <pthread.h>
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107 Portions of this text are reprinted and reproduced in electronic form
108 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
109 -- Portable Operating System Interface (POSIX), The Open Group Base
110 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
111 Electrical and Electronics Engineers, Inc and The Open Group. In the
112 event of any discrepancy between this version and the original IEEE and
113 The Open Group Standard, the original IEEE and The Open Group Standard
114 is the referee document. The original Standard can be obtained online
115 at http://www.opengroup.org/unix/online.html .
116IEEE/The Open Group 2003 PTHREAD_KEY_DELETE(3P)