211 lines
No EOL
8.8 KiB
HTML
211 lines
No EOL
8.8 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
|
||
<HTML>
|
||
<HEAD>
|
||
<META HTTP-EQUIV="CONTENT-TYPE" CONTENT="text/html; charset=utf-8">
|
||
<TITLE>PTHREAD_SPECIFIC(3) manual page</TITLE>
|
||
<META NAME="GENERATOR" CONTENT="OpenOffice.org 1.1.3 (Linux)">
|
||
<META NAME="CREATED" CONTENT="20050504;18425400">
|
||
<META NAME="CHANGED" CONTENT="20050509;18220200">
|
||
<!-- manual page source format generated by PolyglotMan v3.2, -->
|
||
<!-- available at http://polyglotman.sourceforge.net/ -->
|
||
</HEAD>
|
||
<BODY LANG="en-GB" BGCOLOR="#ffffff" DIR="LTR">
|
||
<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> |