196 lines
7.1 KiB
Groff
196 lines
7.1 KiB
Groff
.\" $NetBSD: pthread_key_create.3,v 1.9 2017/10/22 16:37:24 abhinav Exp $
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.\"
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.\" Copyright (c) 2002, 2010 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" Copyright (c) 1996 John Birrell <jb@cimlogic.com.au>.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by John Birrell.
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.\" 4. Neither the name of the author nor the names of any co-contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY JOHN BIRRELL AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD: src/lib/libpthread/man/pthread_key_create.3,v 1.12 2002/09/16 19:29:28 mini Exp $
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.\"
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.Dd May 29, 2015
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.Dt PTHREAD_KEY_CREATE 3
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.Os
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.Sh NAME
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.Nm pthread_key_create ,
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.Nm pthread_key_delete
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.Nd thread-specific data
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.Sh LIBRARY
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.Lb libpthread
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.Sh SYNOPSIS
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.In pthread.h
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.Ft int
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.Fn pthread_key_create "pthread_key_t *key" "void (*destructor)(void *)"
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.Ft int
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.Fn pthread_key_delete "pthread_key_t key"
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.Sh DESCRIPTION
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The
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.Fn pthread_key_create
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function creates a thread-specific data key visible to all threads in the
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process.
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Key values are opaque objects used to locate thread-specific data.
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The same key value may be used by different threads,
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but the values bound to the key by
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.Fn pthread_setspecific
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are maintained on a per-thread basis and
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persist for the life of the calling thread.
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.Pp
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Upon key creation, the value
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.Dv NULL
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is associated with the new key in all active threads.
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Upon thread creation, the value
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.Dv NULL
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is associated with all
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defined keys in the new thread.
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.Pp
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An optional destructor function may be associated with each key value.
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At thread exit, if a key value has a
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.Pf non- Dv NULL
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destructor pointer, and the thread has a
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.Pf non- Dv NULL
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value associated with the key, the function pointed
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to is called with the current associated value as its sole argument.
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The order of destructor calls is unspecified if more
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than one destructor exists for a thread when it exits.
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.Pp
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If, after all the destructors have been called for all
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.Pf non- Dv NULL
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values with associated destructors, there are still some
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.Pf non- Dv NULL
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values with associated destructors, then the process is repeated.
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If, after at least
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.Dv PTHREAD_DESTRUCTOR_ITERATIONS
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iterations of destructor calls for outstanding
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.Pf non- Dv NULL
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values, there are still some
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.Pf non- Dv NULL
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values with
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associated destructors, the implementation stops calling destructors.
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.Pp
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The
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.Fn pthread_key_delete
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function deletes a thread-specific data key previously returned by
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.Fn pthread_key_create .
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The thread-specific data values associated with
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.Fa key
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need not be
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.Dv NULL
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at the time of the call.
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It is the responsibility of the application to free any
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application storage or perform any cleanup actions for data structures
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related to the deleted key or associated thread-specific data in any threads;
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this cleanup can be done either before or after
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.Fn pthread_key_delete
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is called.
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Any attempt to use
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.Fa key
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following the call to
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.Fn pthread_key_delete
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results in undefined behavior.
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.Pp
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The
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.Fn pthread_key_delete
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function itself is callable from within destructor functions,
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but destructor functions are not invoked by the function.
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Any destructor function that may have been associated with
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.Fa key
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will no longer be called upon thread exit.
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.Sh RETURN VALUES
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If successful, the
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.Fn pthread_key_create
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function will store the newly created key value at the location specified by
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.Fa key
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and returns zero.
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Also
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.Fn pthread_key_delete
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will return zero upon success.
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Upon failure both functions return an error number to indicate the cause.
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.Sh ENVIRONMENT
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.Bl -tag -width PTHREAD_KEYS_MAX
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.It Ev PTHREAD_KEYS_MAX
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Maximum per-process thread-specific data keys.
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This cannot be set below
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.Dv _POSIX_THREAD_KEYS_MAX .
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.El
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.Sh ERRORS
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The
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.Fn pthread_key_create
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may fail if:
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.Bl -tag -width Er
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.It Bq Er EAGAIN
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The system lacked the necessary resources to create another thread-specific
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data key, or the system-imposed limit on the total number of keys per-process
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.Dv PTHREAD_KEYS_MAX
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would be exceeded.
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.It Bq Er ENOMEM
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Insufficient memory exists to create the key.
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.El
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.Pp
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The
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.Fn pthread_key_delete
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function may fail if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The
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.Fa key
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value is invalid.
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.El
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.Sh SEE ALSO
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.Xr pthread_getspecific 3
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.Sh STANDARDS
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These functions conform to
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.St -p1003.1-2001 .
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.Sh BUGS
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The current specifications are flawed and
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do not permit a clean implementation without potential problems.
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The current implementation in
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.Nx
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addresses these problems by not supporting key reuse.
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