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 <H4>POSIX Threads for Windows – REFERENCE - <A HREF="http://sources.redhat.com/pthreads-win32">Pthreads-w32</A></H4>
 <P><A HREF="index.html">Reference Index</A></P>
 <P><A HREF="#toc">Table of Contents</A></P>
 <H2><A HREF="#toc0" NAME="sect0">Name</A></H2>
 <P>pthread_key_create, pthread_key_delete, pthread_setspecific,
 pthread_getspecific - management of thread-specific data
 </P>
 <H2><A HREF="#toc1" NAME="sect1">Synopsis</A></H2>
 <P><B>#include &lt;pthread.h&gt;</B>
 </P>
 <P><B>int pthread_key_create(pthread_key_t *</B><I>key</I><B>, void
 (*</B><I>destr_function</I><B>) (void *));</B>
 </P>
 <P><B>int pthread_key_delete(pthread_key_t </B><I>key</I><B>);</B>
 </P>
 <P><B>int pthread_setspecific(pthread_key_t </B><I>key</I><B>, const
 void *</B><I>pointer</I><B>);</B>
 </P>
 <P><B>void * pthread_getspecific(pthread_key_t </B><I>key</I><B>);</B>
 </P>
 <H2><A HREF="#toc2" NAME="sect2">Description</A></H2>
 <P>Programs often need global or static variables that have different
 values in different threads. Since threads share one memory space,
 this cannot be achieved with regular variables. Thread-specific data
 is the POSIX threads answer to this need.
 </P>
 <P>Each thread possesses a private memory block, the thread-specific
 data area, or TSD area for short. This area is indexed by TSD keys.
 The TSD area associates values of type <B>void *</B> to TSD keys. TSD
 keys are common to all threads, but the value associated with a given
 TSD key can be different in each thread.
 </P>
 <P>For concreteness, the TSD areas can be viewed as arrays of <B>void
 *</B> pointers, TSD keys as integer indices into these arrays, and
 the value of a TSD key as the value of the corresponding array
 element in the calling thread.
 </P>
 <P>When a thread is created, its TSD area initially associates <B>NULL</B>
 with all keys.
 </P>
 <P><B>pthread_key_create</B> allocates a new TSD key. The key is
 stored in the location pointed to by <I>key</I>. There is a limit of
 <B>PTHREAD_KEYS_MAX</B> on the number of keys allocated at a given
 time. The value initially associated with the returned key is <B>NULL</B>
 in all currently executing threads.
 </P>
 <P>The <I>destr_function</I> argument, if not <B>NULL</B>, specifies
 a destructor function associated with the key. When a thread
 terminates via <B>pthread_exit</B> or by cancellation, <I>destr_function</I>
 is called with arguments the value associated with the key in that
 thread. The <I>destr_function</I> is not called if that value is <B>NULL</B><SPAN STYLE="font-weight: medium">
 or the key has been deleted</SPAN>. The order in which destructor
 functions are called at thread termination time is unspecified.
 </P>
 <P>Before the destructor function is called, the <B>NULL</B> value is
 associated with the key in the current thread. A destructor function
 might, however, re-associate non- <B>NULL</B> values to that key or
 some other key. To deal with this, if after all the destructors have
 been called for all non- <B>NULL</B> values, there are still some
 non- <B>NULL</B> values with associated destructors, then the process
 is repeated.</P>
 <P><B>pthread_key_delete</B> deallocates a TSD key. It does not check
 whether non- <B>NULL</B> values are associated with that key in the
 currently executing threads, nor call the destructor function
 associated with the key.
 </P>
 <P><B>pthread_setspecific</B> changes the value associated with <I>key</I>
 in the calling thread, storing the given <I>pointer</I> instead.
 </P>
 <P><B>pthread_getspecific</B> returns the value currently associated
 with <I>key</I> in the calling thread.
 </P>
 <P>The routines <B>pthread_setspecific</B>, <B>pthread_getspecific</B>,
 and <B>pthread_key_delete</B> can be called from <I>destr_function</I>
 targeting any valid key including the key on which <I>destr_function</I>
 is currently operating. If <B>pthread_getspecific</B> is called on
 the key whose thread specific data is being destroyed, the value NULL
 is returned, unless <B>pthread_setspecific</B> was called previously
 on that key from within <I>destr_function</I> to set the value to
 non-NULL. For some implementations the effect of calling
 <B>pthread_setspecific</B> from within <I>destr_function</I> can be
 either memory leakage or infinite loops if <I>destr_function</I> has
 already been called at least <B>PTHREAD_DESTRUCTOR_ITERATIONS</B>
 times.</P>
 <P STYLE="font-weight: medium"><B>Pthreads-w32</B> stops running key
 <I>destr_function</I> routines after <B>PTHREAD_DESTRUCTOR_ITERATIONS</B>
 iterations, even if some non- <B>NULL</B> values with associated
 descriptors remain. If memory is allocated and associated with a key
 from within <I>destr_function</I>, that memory may not be reclaimed
 because that key's <I>destr_function</I>, may not run again.</P>
 <H2><A HREF="#toc3" NAME="sect3">Return Value</A></H2>
 <P><B>pthread_key_create</B>, <B>pthread_key_delete</B>, and
 <B>pthread_setspecific</B> return 0 on success and a non-zero error
 code on failure. If successful, <B>pthread_key_create</B> stores the
 newly allocated key in the location pointed to by its <I>key</I>
 argument.
 </P>
 <P><B>pthread_getspecific</B> returns the value associated with <I>key</I>
 on success, and <B>NULL</B> on error.
 </P>
 <H2><A HREF="#toc4" NAME="sect4">Errors</A></H2>
 <P><B>pthread_key_create</B> returns the following error code on
 error:
 </P>
 <DL>
 	<DL>
 		<DT STYLE="margin-right: 1cm; margin-bottom: 0.5cm"><B>EAGAIN</B>
 		</DT></DL>
 </DL>
 <BLOCKQUOTE STYLE="margin-left: 5cm">
 <B>PTHREAD_KEYS_MAX</B> keys are already allocated
 </BLOCKQUOTE>
 <DL>
 	<DL>
 		<DT STYLE="margin-right: 1cm; margin-bottom: 0.5cm"><B>ENOMEM</B>
 		</DT></DL>
 </DL>
 <BLOCKQUOTE STYLE="margin-left: 5cm">
 Insufficient memory to allocate the key.
 </BLOCKQUOTE>
 <P><B>pthread_key_delete</B> and <B>pthread_setspecific</B> return
 the following error code on error:
 </P>
 <DL>
 	<DL>
 		<DT STYLE="margin-right: 1cm; margin-bottom: 0.5cm"><B>EINVAL</B>
 		</DT><DD STYLE="margin-right: 1cm; margin-bottom: 0.5cm">
 		<I>key</I> is not a valid, allocated TSD key
 		</DD></DL>
 </DL>
 <P>
 <B>pthread_getspecific</B> returns <B>NULL</B> if <I>key</I> is not a
 valid, allocated TSD key.
 </P>
 <H2><A HREF="#toc5" NAME="sect5">Author</A></H2>
 <P>Xavier Leroy &lt;Xavier.Leroy@inria.fr&gt;
 </P>
 <P>Modified by Ross Johnson for use with <A HREF="http://sources.redhat.com/pthreads-win32">Pthreads-w32</A>.</P>
 <H2><A HREF="#toc6" NAME="sect6">See Also</A></H2>
 <P><A HREF="pthread_create.html">pthread_create(3)</A> ,
 <A HREF="pthread_exit.html">pthread_exit(3)</A> ,
 <A HREF="pthread_cancel.html">pthread_testcancel(3)</A> .
 </P>
 <H2><A HREF="#toc7" NAME="sect7">Example</A></H2>
 <P>The following code fragment allocates a thread-specific array of
 100 characters, with automatic reclamation at thread exit:
 </P>
 <BLOCKQUOTE><BR><BR>
 </BLOCKQUOTE>
 <PRE STYLE="margin-left: 1cm; margin-right: 1cm">/* Key for the thread-specific buffer */
 static pthread_key_t buffer_key;
 /* Once-only initialisation of the key */
 static pthread_once_t buffer_key_once = PTHREAD_ONCE_INIT;
 /* Allocate the thread-specific buffer */
 void buffer_alloc(void)
 {
   pthread_once(&amp;buffer_key_once, buffer_key_alloc);
   pthread_setspecific(buffer_key, malloc(100));
 }
 /* Return the thread-specific buffer */
 char * get_buffer(void)
 {
   return (char *) pthread_getspecific(buffer_key);
 }
 /* Allocate the key */
 static void buffer_key_alloc()
 {
   pthread_key_create(&amp;buffer_key, buffer_destroy);
 }
 /* Free the thread-specific buffer */
 static void buffer_destroy(void * buf)
 {
   free(buf);
 }</PRE>
 <HR>
 <BLOCKQUOTE STYLE="margin-left: 0cm; margin-right: 0cm"><A NAME="toc"></A>
 <B>Table of Contents</B></BLOCKQUOTE>
 <UL>
 	<LI><BLOCKQUOTE STYLE="margin-bottom: 0cm"><A HREF="#sect0" NAME="toc0">Name</A>
 		</BLOCKQUOTE>
 	<LI><BLOCKQUOTE STYLE="margin-bottom: 0cm"><A HREF="#sect1" NAME="toc1">Synopsis</A>
 		</BLOCKQUOTE>
 	<LI><BLOCKQUOTE STYLE="margin-bottom: 0cm"><A HREF="#sect2" NAME="toc2">Description</A>
 		</BLOCKQUOTE>
 	<LI><BLOCKQUOTE STYLE="margin-bottom: 0cm"><A HREF="#sect3" NAME="toc3">Return
 	Value</A>
 	</BLOCKQUOTE>
 	<LI><BLOCKQUOTE STYLE="margin-bottom: 0cm"><A HREF="#sect4" NAME="toc4">Errors</A>
 		</BLOCKQUOTE>
 	<LI><BLOCKQUOTE STYLE="margin-bottom: 0cm"><A HREF="#sect5" NAME="toc5">Author</A>
 		</BLOCKQUOTE>
 	<LI><BLOCKQUOTE STYLE="margin-bottom: 0cm"><A HREF="#sect6" NAME="toc6">See
 	Also</A>
 	</BLOCKQUOTE>
 	<LI><BLOCKQUOTE><A HREF="#sect7" NAME="toc7">Example</A>
 	</BLOCKQUOTE>
 </UL>
 </BODY>
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	<H4>POSIX Threads for Windows – REFERENCE - <A HREF="http://sources.redhat.com/pthreads-win32">Pthreads-w32</A></H4>
	<P><A HREF="index.html">Reference Index</A></P>
	<P><A HREF="#toc">Table of Contents</A></P>
	<H2><A HREF="#toc0" NAME="sect0">Name</A></H2>
	<P>pthread_key_create, pthread_key_delete, pthread_setspecific,
	pthread_getspecific - management of thread-specific data
	</P>
	<H2><A HREF="#toc1" NAME="sect1">Synopsis</A></H2>
	<P><B>#include <pthread.h></B>
	</P>
	<P><B>int pthread_key_create(pthread_key_t *</B><I>key</I><B>, void
	(</B><I>destr_function</I><B>) (void ));</B>
	</P>
	<P><B>int pthread_key_delete(pthread_key_t </B><I>key</I><B>);</B>
	</P>
	<P><B>int pthread_setspecific(pthread_key_t </B><I>key</I><B>, const
	void *</B><I>pointer</I><B>);</B>
	</P>
	<P><B>void * pthread_getspecific(pthread_key_t </B><I>key</I><B>);</B>
	</P>
	<H2><A HREF="#toc2" NAME="sect2">Description</A></H2>
	<P>Programs often need global or static variables that have different
	values in different threads. Since threads share one memory space,
	this cannot be achieved with regular variables. Thread-specific data
	is the POSIX threads answer to this need.
	</P>
	<P>Each thread possesses a private memory block, the thread-specific
	data area, or TSD area for short. This area is indexed by TSD keys.
	The TSD area associates values of type <B>void *</B> to TSD keys. TSD
	keys are common to all threads, but the value associated with a given
	TSD key can be different in each thread.
	</P>
	<P>For concreteness, the TSD areas can be viewed as arrays of <B>void
	*</B> pointers, TSD keys as integer indices into these arrays, and
	the value of a TSD key as the value of the corresponding array
	element in the calling thread.
	</P>
	<P>When a thread is created, its TSD area initially associates <B>NULL</B>
	with all keys.
	</P>
	<P><B>pthread_key_create</B> allocates a new TSD key. The key is
	stored in the location pointed to by <I>key</I>. There is a limit of
	<B>PTHREAD_KEYS_MAX</B> on the number of keys allocated at a given
	time. The value initially associated with the returned key is <B>NULL</B>
	in all currently executing threads.
	</P>
	<P>The <I>destr_function</I> argument, if not <B>NULL</B>, specifies
	a destructor function associated with the key. When a thread
	terminates via <B>pthread_exit</B> or by cancellation, <I>destr_function</I>
	is called with arguments the value associated with the key in that
	thread. The <I>destr_function</I> is not called if that value is <B>NULL</B><SPAN STYLE="font-weight: medium">
	or the key has been deleted</SPAN>. The order in which destructor
	functions are called at thread termination time is unspecified.
	</P>
	<P>Before the destructor function is called, the <B>NULL</B> value is
	associated with the key in the current thread. A destructor function
	might, however, re-associate non- <B>NULL</B> values to that key or
	some other key. To deal with this, if after all the destructors have
	been called for all non- <B>NULL</B> values, there are still some
	non- <B>NULL</B> values with associated destructors, then the process
	is repeated.</P>
	<P><B>pthread_key_delete</B> deallocates a TSD key. It does not check
	whether non- <B>NULL</B> values are associated with that key in the
	currently executing threads, nor call the destructor function
	associated with the key.
	</P>
	<P><B>pthread_setspecific</B> changes the value associated with <I>key</I>
	in the calling thread, storing the given <I>pointer</I> instead.
	</P>
	<P><B>pthread_getspecific</B> returns the value currently associated
	with <I>key</I> in the calling thread.
	</P>
	<P>The routines <B>pthread_setspecific</B>, <B>pthread_getspecific</B>,
	and <B>pthread_key_delete</B> can be called from <I>destr_function</I>
	targeting any valid key including the key on which <I>destr_function</I>
	is currently operating. If <B>pthread_getspecific</B> is called on
	the key whose thread specific data is being destroyed, the value NULL
	is returned, unless <B>pthread_setspecific</B> was called previously
	on that key from within <I>destr_function</I> to set the value to
	non-NULL. For some implementations the effect of calling
	<B>pthread_setspecific</B> from within <I>destr_function</I> can be
	either memory leakage or infinite loops if <I>destr_function</I> has
	already been called at least <B>PTHREAD_DESTRUCTOR_ITERATIONS</B>
	times.</P>
	<P STYLE="font-weight: medium"><B>Pthreads-w32</B> stops running key
	<I>destr_function</I> routines after <B>PTHREAD_DESTRUCTOR_ITERATIONS</B>
	iterations, even if some non- <B>NULL</B> values with associated
	descriptors remain. If memory is allocated and associated with a key
	from within <I>destr_function</I>, that memory may not be reclaimed
	because that key's <I>destr_function</I>, may not run again.</P>
	<H2><A HREF="#toc3" NAME="sect3">Return Value</A></H2>
	<P><B>pthread_key_create</B>, <B>pthread_key_delete</B>, and
	<B>pthread_setspecific</B> return 0 on success and a non-zero error
	code on failure. If successful, <B>pthread_key_create</B> stores the
	newly allocated key in the location pointed to by its <I>key</I>
	argument.
	</P>
	<P><B>pthread_getspecific</B> returns the value associated with <I>key</I>
	on success, and <B>NULL</B> on error.
	</P>
	<H2><A HREF="#toc4" NAME="sect4">Errors</A></H2>
	<P><B>pthread_key_create</B> returns the following error code on
	error:
	</P>
	<DL>
	<DL>
	<DT STYLE="margin-right: 1cm; margin-bottom: 0.5cm"><B>EAGAIN</B>
	</DT></DL>
	</DL>
	<BLOCKQUOTE STYLE="margin-left: 5cm">
	<B>PTHREAD_KEYS_MAX</B> keys are already allocated
	</BLOCKQUOTE>
	<DL>
	<DL>
	<DT STYLE="margin-right: 1cm; margin-bottom: 0.5cm"><B>ENOMEM</B>
	</DT></DL>
	</DL>
	<BLOCKQUOTE STYLE="margin-left: 5cm">
	Insufficient memory to allocate the key.
	</BLOCKQUOTE>
	<P><B>pthread_key_delete</B> and <B>pthread_setspecific</B> return
	the following error code on error:
	</P>
	<DL>
	<DL>
	<DT STYLE="margin-right: 1cm; margin-bottom: 0.5cm"><B>EINVAL</B>
	</DT><DD STYLE="margin-right: 1cm; margin-bottom: 0.5cm">
	<I>key</I> is not a valid, allocated TSD key
	</DD></DL>
	</DL>
	<P>
	<B>pthread_getspecific</B> returns <B>NULL</B> if <I>key</I> is not a
	valid, allocated TSD key.
	</P>
	<H2><A HREF="#toc5" NAME="sect5">Author</A></H2>
	<P>Xavier Leroy <Xavier.Leroy@inria.fr>
	</P>
	<P>Modified by Ross Johnson for use with <A HREF="http://sources.redhat.com/pthreads-win32">Pthreads-w32</A>.</P>
	<H2><A HREF="#toc6" NAME="sect6">See Also</A></H2>
	<P><A HREF="pthread_create.html">pthread_create(3)</A> ,
	<A HREF="pthread_exit.html">pthread_exit(3)</A> ,
	<A HREF="pthread_cancel.html">pthread_testcancel(3)</A> .
	</P>
	<H2><A HREF="#toc7" NAME="sect7">Example</A></H2>
	<P>The following code fragment allocates a thread-specific array of
	100 characters, with automatic reclamation at thread exit:
	</P>
	<BLOCKQUOTE><BR><BR>
	</BLOCKQUOTE>
	<PRE STYLE="margin-left: 1cm; margin-right: 1cm">/* Key for the thread-specific buffer */
	static pthread_key_t buffer_key;
	/* Once-only initialisation of the key */
	static pthread_once_t buffer_key_once = PTHREAD_ONCE_INIT;
	/* Allocate the thread-specific buffer */
	void buffer_alloc(void)
	{
	pthread_once(&buffer_key_once, buffer_key_alloc);
	pthread_setspecific(buffer_key, malloc(100));
	}
	/* Return the thread-specific buffer */
	char * get_buffer(void)
	{
	return (char *) pthread_getspecific(buffer_key);
	}
	/* Allocate the key */
	static void buffer_key_alloc()
	{
	pthread_key_create(&buffer_key, buffer_destroy);
	}
	/* Free the thread-specific buffer */
	static void buffer_destroy(void * buf)
	{
	free(buf);
	}</PRE>
	<HR>
	<BLOCKQUOTE STYLE="margin-left: 0cm; margin-right: 0cm"><A NAME="toc"></A>
	<B>Table of Contents</B></BLOCKQUOTE>
	<UL>
	<LI><BLOCKQUOTE STYLE="margin-bottom: 0cm"><A HREF="#sect0" NAME="toc0">Name</A>
	</BLOCKQUOTE>
	<LI><BLOCKQUOTE STYLE="margin-bottom: 0cm"><A HREF="#sect1" NAME="toc1">Synopsis</A>
	</BLOCKQUOTE>
	<LI><BLOCKQUOTE STYLE="margin-bottom: 0cm"><A HREF="#sect2" NAME="toc2">Description</A>
	</BLOCKQUOTE>
	<LI><BLOCKQUOTE STYLE="margin-bottom: 0cm"><A HREF="#sect3" NAME="toc3">Return
	Value</A>
	</BLOCKQUOTE>
	<LI><BLOCKQUOTE STYLE="margin-bottom: 0cm"><A HREF="#sect4" NAME="toc4">Errors</A>
	</BLOCKQUOTE>
	<LI><BLOCKQUOTE STYLE="margin-bottom: 0cm"><A HREF="#sect5" NAME="toc5">Author</A>
	</BLOCKQUOTE>
	<LI><BLOCKQUOTE STYLE="margin-bottom: 0cm"><A HREF="#sect6" NAME="toc6">See
	Also</A>
	</BLOCKQUOTE>
	<LI><BLOCKQUOTE><A HREF="#sect7" NAME="toc7">Example</A>
	</BLOCKQUOTE>
	</UL>
	</BODY>
	</HTML>