Originální popis anglicky:
pthread_key_delete - thread-specific data key deletion
Návod, kniha: POSIX Programmer's Manual
#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 may fail if:
- EINVAL
- The key value is invalid.
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.
None.
pthread_key_create() , the Base Definitions volume of
IEEE Std 1003.1-2001,
<pthread.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 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
.
