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<title>Xenomai API: Thread cancellation.</title>
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<h1>Thread cancellation.<br>
<small>
[<a class="el" href="group__posix__thread.html">Threads management services.</a>]</small>
</h1>
<p>
<div class="dynheader">
Collaboration diagram for Thread cancellation.:</div>
<div class="dynsection">
<center><table><tr><td><img src="group__posix__cancel.png" border="0" alt="" usemap="#group____posix____cancel_map">
<map name="group____posix____cancel_map">
<area shape="rect" href="group__posix__thread.html" title="Threads management services." alt="" coords="5,5,229,32"></map></td></tr></table></center>
</div>
<hr><a name="_details"></a><h2>Detailed Description</h2>
Thread cancellation.
<p>
Cancellation is the mechanism by which a thread can terminate the execution of a Xenomai POSIX skin thread (created with <a class="el" href="group__posix__thread.html#ge6e819ed048e4c4a4ee96fa6f426852c" title="Create a thread.">pthread_create()</a>). More precisely, a thread can send a cancellation request to a Xenomai POSIX skin thread and depending on its cancelability type (see <a class="el" href="group__posix__cancel.html#g636480bad96654729ecf18017c2820cd" title="Set cancelability type of the current thread.">pthread_setcanceltype()</a>) and state (see <a class="el" href="group__posix__cancel.html#ge377201f61fae5f551dfd7eb6de75873" title="Set cancelability state of the current thread.">pthread_setcancelstate()</a>), the target thread can then either ignore the request, honor it immediately, or defer it till it reaches a cancellation point. When threads are first created by <a class="el" href="group__posix__thread.html#ge6e819ed048e4c4a4ee96fa6f426852c" title="Create a thread.">pthread_create()</a>, they always defer cancellation requests.<p>
When a thread eventually honors a cancellation request, it behaves as if <em>pthread_exit(PTHREAD_CANCELED)</em> was called. All cleanup handlers are executed in reverse order, finalization functions for thread-specific data are called, and finally the thread stops executing. If the canceled thread was joinable, the return value PTHREAD_CANCELED is provided to whichever thread calls <a class="el" href="group__posix__thread.html#ga79c99cc7b194918a2def257246f11c6" title="Wait for termination of a specified thread.">pthread_join()</a> on it. See <a class="el" href="group__posix__thread.html#g090bdc13141e76205fab4cb3c5fab0e4" title="Terminate the current thread.">pthread_exit()</a> for more information.<p>
Cancellation points are the points where the thread checks for pending cancellation requests and performs them. The POSIX threads functions <a class="el" href="group__posix__thread.html#ga79c99cc7b194918a2def257246f11c6" title="Wait for termination of a specified thread.">pthread_join()</a>, <a class="el" href="group__posix__cond.html#g03a32b6f066162e62f274dfcb58338eb" title="Wait on a condition variable.">pthread_cond_wait()</a>, <a class="el" href="group__posix__cond.html#gfc43955fc3f1cb43723a9e0be19d0ad1" title="Wait a bounded time on a condition variable.">pthread_cond_timedwait()</a>, <a class="el" href="group__posix__cancel.html#gf1c95282ab2bea25f0888a19652cd41f" title="Test if a cancellation request is pending.">pthread_testcancel()</a>, <a class="el" href="group__posix__sem.html#g1b9226cb6b1c40511c025309c0b6b2ee" title="Lock a semaphore.">sem_wait()</a>, <a class="el" href="group__posix__sem.html#g8678e7f5136343ef8d8123a185878f78" title="Attempt, during a bounded time, to lock a semaphore.">sem_timedwait()</a>, <a class="el" href="group__posix__signal.html#gdc0d6eabea5878a70fe1f97b002f5f2a" title="Wait for signals.">sigwait()</a>, <a class="el" href="group__posix__signal.html#gc9043e9dc6fc22bfb82606932bb3b3ed" title="Wait for signals.">sigwaitinfo()</a> and <a class="el" href="group__posix__signal.html#g04cbfbf6045492b2273cc8046cd52d08" title="Wait during a bounded time for signals.">sigtimedwait()</a> are cancellation points.<p>
<dl class="see" compact><dt><b>See also:</b></dt><dd><a href="http://www.opengroup.org/onlinepubs/000095399/functions/xsh_chap02_09.html#tag_02_09_05">Specification.</a> </dd></dl>
<p>
<table border="0" cellpadding="0" cellspacing="0">
<tr><td></td></tr>
<tr><td colspan="2"><br><h2>Functions</h2></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top">int </td><td class="memItemRight" valign="bottom"><a class="el" href="group__posix__cancel.html#g9e77a80c073787bf9a593e9c619dce27">pthread_cancel</a> (pthread_t thread)</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Cancel a thread. <a href="#g9e77a80c073787bf9a593e9c619dce27"></a><br></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top">void </td><td class="memItemRight" valign="bottom"><a class="el" href="group__posix__cancel.html#g2032ad0c2fbd9d0af855da85ce314c36">pthread_cleanup_push</a> (cleanup_routine_t *routine, void *arg)</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Register a cleanup handler to be executed at the time of cancellation. <a href="#g2032ad0c2fbd9d0af855da85ce314c36"></a><br></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top">void </td><td class="memItemRight" valign="bottom"><a class="el" href="group__posix__cancel.html#gfbe33fb00cd24693796a0870a3374631">pthread_cleanup_pop</a> (int execute)</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Unregister the last registered cleanup handler. <a href="#gfbe33fb00cd24693796a0870a3374631"></a><br></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top">int </td><td class="memItemRight" valign="bottom"><a class="el" href="group__posix__cancel.html#g636480bad96654729ecf18017c2820cd">pthread_setcanceltype</a> (int type, int *oldtype_ptr)</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Set cancelability type of the current thread. <a href="#g636480bad96654729ecf18017c2820cd"></a><br></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top">int </td><td class="memItemRight" valign="bottom"><a class="el" href="group__posix__cancel.html#ge377201f61fae5f551dfd7eb6de75873">pthread_setcancelstate</a> (int state, int *oldstate_ptr)</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Set cancelability state of the current thread. <a href="#ge377201f61fae5f551dfd7eb6de75873"></a><br></td></tr>
<tr><td class="memItemLeft" nowrap align="right" valign="top">void </td><td class="memItemRight" valign="bottom"><a class="el" href="group__posix__cancel.html#gf1c95282ab2bea25f0888a19652cd41f">pthread_testcancel</a> (void)</td></tr>
<tr><td class="mdescLeft"> </td><td class="mdescRight">Test if a cancellation request is pending. <a href="#gf1c95282ab2bea25f0888a19652cd41f"></a><br></td></tr>
</table>
<hr><h2>Function Documentation</h2>
<a class="anchor" name="g9e77a80c073787bf9a593e9c619dce27"></a><!-- doxytag: member="cancel.c::pthread_cancel" ref="g9e77a80c073787bf9a593e9c619dce27" args="(pthread_t thread)" -->
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<td class="memname">int pthread_cancel </td>
<td>(</td>
<td class="paramtype">pthread_t </td>
<td class="paramname"> <em>thread</em> </td>
<td> ) </td>
<td></td>
</tr>
</table>
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<div class="memdoc">
<p>
Cancel a thread.
<p>
This service sends a cancellation request to the thread <em>thread</em> and returns immediately. Depending on the target thread cancelability state (see <a class="el" href="group__posix__cancel.html#ge377201f61fae5f551dfd7eb6de75873" title="Set cancelability state of the current thread.">pthread_setcancelstate()</a>) and type (see <a class="el" href="group__posix__cancel.html#g636480bad96654729ecf18017c2820cd" title="Set cancelability type of the current thread.">pthread_setcanceltype()</a>), its termination is either immediate, deferred or ignored.<p>
When the cancellation request is handled and before the thread is terminated, the cancellation cleanup handlers (registered with the <a class="el" href="group__posix__cancel.html#g2032ad0c2fbd9d0af855da85ce314c36" title="Register a cleanup handler to be executed at the time of cancellation.">pthread_cleanup_push()</a> service) are called, then the thread-specific data destructor functions (registered with <a class="el" href="group__posix__tsd.html#gf4b7ced8ecff505380fe8216244a3764" title="Create a thread-specific data key.">pthread_key_create()</a>).<p>
<dl class="return" compact><dt><b>Returns:</b></dt><dd>0 on success; <p>
an error number if:<ul>
<li>ESRCH, the thread <em>thread</em> was not found.</li></ul>
</dd></dl>
<dl class="see" compact><dt><b>See also:</b></dt><dd><a href="http://www.opengroup.org/onlinepubs/000095399/functions/pthread_cancel.html">Specification.</a> </dd></dl>
<p>References <a class="el" href="pod_8h-source.html#l00251">xnpod_schedule()</a>, and <a class="el" href="pod_8c-source.html#l01713">xnpod_unblock_thread()</a>.</p>
<p>Referenced by <a class="el" href="src_2skins_2native_2task_8c-source.html#l00257">rt_task_delete()</a>.</p>
</div>
</div><p>
<a class="anchor" name="gfbe33fb00cd24693796a0870a3374631"></a><!-- doxytag: member="cancel.c::pthread_cleanup_pop" ref="gfbe33fb00cd24693796a0870a3374631" args="(int execute)" -->
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<td class="memname">void pthread_cleanup_pop </td>
<td>(</td>
<td class="paramtype">int </td>
<td class="paramname"> <em>execute</em> </td>
<td> ) </td>
<td></td>
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<div class="memdoc">
<p>
Unregister the last registered cleanup handler.
<p>
If the calling thread is a Xenomai POSIX skin thread (i.e. created with <a class="el" href="group__posix__thread.html#ge6e819ed048e4c4a4ee96fa6f426852c" title="Create a thread.">pthread_create()</a>), this service unregisters the last routine which was registered with <a class="el" href="group__posix__cancel.html#g2032ad0c2fbd9d0af855da85ce314c36" title="Register a cleanup handler to be executed at the time of cancellation.">pthread_cleanup_push()</a> and call it if <em>execute</em> is not null.<p>
If the caller context is invalid (not a Xenomai POSIX skin thread), this service has no effect.<p>
This service may be called at any place, but for maximal portability, should only called in the same lexical scope as the matching call to <a class="el" href="group__posix__cancel.html#g2032ad0c2fbd9d0af855da85ce314c36" title="Register a cleanup handler to be executed at the time of cancellation.">pthread_cleanup_push()</a>.<p>
<dl compact><dt><b>Parameters:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>execute</em> </td><td>if non zero, the last registered cleanup handler should be executed before it is unregistered.</td></tr>
</table>
</dl>
<dl class="user" compact><dt><b>Valid contexts:</b></dt><dd><ul>
<li>Xenomai POSIX skin kernel-space thread,</li><li>Xenomai POSIX skin user-space thread (switches to primary mode).</li></ul>
</dd></dl>
<dl class="see" compact><dt><b>See also:</b></dt><dd><a href="http://www.opengroup.org/onlinepubs/000095399/functions/pthread_cleanup_pop.html">Specification.</a> </dd></dl>
<p>Referenced by <a class="el" href="src_2skins_2native_2cond_8c-source.html#l00065">rt_cond_wait()</a>, and <a class="el" href="src_2skins_2native_2cond_8c-source.html#l00115">rt_cond_wait_until()</a>.</p>
</div>
</div><p>
<a class="anchor" name="g2032ad0c2fbd9d0af855da85ce314c36"></a><!-- doxytag: member="cancel.c::pthread_cleanup_push" ref="g2032ad0c2fbd9d0af855da85ce314c36" args="(cleanup_routine_t *routine, void *arg)" -->
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<td class="memname">void pthread_cleanup_push </td>
<td>(</td>
<td class="paramtype">cleanup_routine_t * </td>
<td class="paramname"> <em>routine</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">void * </td>
<td class="paramname"> <em>arg</em></td><td> </td>
</tr>
<tr>
<td></td>
<td>)</td>
<td></td><td></td><td></td>
</tr>
</table>
</div>
<div class="memdoc">
<p>
Register a cleanup handler to be executed at the time of cancellation.
<p>
This service registers the given <em>routine</em> to be executed a the time of cancellation of the calling thread, if this thread is a Xenomai POSIX skin thread (i.e. created with the <a class="el" href="group__posix__thread.html#ge6e819ed048e4c4a4ee96fa6f426852c" title="Create a thread.">pthread_create()</a> service). If the caller context is invalid (not a Xenomai POSIX skin thread), this service has no effect.<p>
If allocation from the system heap fails (because the system heap size is to small), this service fails silently.<p>
The routines registered with this service get called in LIFO order when the calling thread calls <a class="el" href="group__posix__thread.html#g090bdc13141e76205fab4cb3c5fab0e4" title="Terminate the current thread.">pthread_exit()</a> or is canceled, or when it calls the <a class="el" href="group__posix__cancel.html#gfbe33fb00cd24693796a0870a3374631" title="Unregister the last registered cleanup handler.">pthread_cleanup_pop()</a> service with a non null argument.<p>
<dl compact><dt><b>Parameters:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>routine</em> </td><td>the cleanup routine to be registered;</td></tr>
<tr><td valign="top"></td><td valign="top"><em>arg</em> </td><td>the argument associated with this routine.</td></tr>
</table>
</dl>
<dl class="user" compact><dt><b>Valid contexts:</b></dt><dd><ul>
<li>Xenomai POSIX skin kernel-space thread,</li><li>Xenomai POSIX skin user-space thread (switches to primary mode).</li></ul>
</dd></dl>
<dl class="see" compact><dt><b>See also:</b></dt><dd><a href="http://www.opengroup.org/onlinepubs/000095399/functions/pthread_cleanup_push.html">Specification.</a> </dd></dl>
<p>Referenced by <a class="el" href="src_2skins_2native_2cond_8c-source.html#l00065">rt_cond_wait()</a>, and <a class="el" href="src_2skins_2native_2cond_8c-source.html#l00115">rt_cond_wait_until()</a>.</p>
</div>
</div><p>
<a class="anchor" name="ge377201f61fae5f551dfd7eb6de75873"></a><!-- doxytag: member="cancel.c::pthread_setcancelstate" ref="ge377201f61fae5f551dfd7eb6de75873" args="(int state, int *oldstate_ptr)" -->
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<td class="memname">int pthread_setcancelstate </td>
<td>(</td>
<td class="paramtype">int </td>
<td class="paramname"> <em>state</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">int * </td>
<td class="paramname"> <em>oldstate_ptr</em></td><td> </td>
</tr>
<tr>
<td></td>
<td>)</td>
<td></td><td></td><td></td>
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<div class="memdoc">
<p>
Set cancelability state of the current thread.
<p>
This service atomically set the cancelability state of the calling thread and returns its previous value at the address <em>oldstate_ptr</em>, if the calling thread is a Xenomai POSIX skin thread (i.e. created with the pthread_create service).<p>
The cancelability state of a POSIX thread may be:<ul>
<li>PTHREAD_CANCEL_ENABLE, meaning that cancellation requests will be handled if received;</li><li>PTHREAD_CANCEL_DISABLE, meaning that cancellation requests will not be handled if received.</li></ul>
<p>
<dl compact><dt><b>Parameters:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>state</em> </td><td>new cancelability state of the calling thread;</td></tr>
<tr><td valign="top"></td><td valign="top"><em>oldstate_ptr</em> </td><td>address where the old cancelability state will be stored on success.</td></tr>
</table>
</dl>
<dl class="return" compact><dt><b>Returns:</b></dt><dd>0 on success; <p>
an error number if:<ul>
<li>EINVAL, <em>state</em> is not a valid cancelability state;</li><li>EPERM, the caller context is invalid.</li></ul>
</dd></dl>
<dl class="user" compact><dt><b>Valid contexts:</b></dt><dd><ul>
<li>Xenomai POSIX skin kernel-space thread,</li><li>Xenomai POSIX skin user-space thread (switches to primary mode).</li></ul>
</dd></dl>
<dl class="see" compact><dt><b>See also:</b></dt><dd><a href="http://www.opengroup.org/onlinepubs/000095399/functions/pthread_setcancelstate.html">Specification.</a> </dd></dl>
</div>
</div><p>
<a class="anchor" name="g636480bad96654729ecf18017c2820cd"></a><!-- doxytag: member="cancel.c::pthread_setcanceltype" ref="g636480bad96654729ecf18017c2820cd" args="(int type, int *oldtype_ptr)" -->
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<td class="memname">int pthread_setcanceltype </td>
<td>(</td>
<td class="paramtype">int </td>
<td class="paramname"> <em>type</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">int * </td>
<td class="paramname"> <em>oldtype_ptr</em></td><td> </td>
</tr>
<tr>
<td></td>
<td>)</td>
<td></td><td></td><td></td>
</tr>
</table>
</div>
<div class="memdoc">
<p>
Set cancelability type of the current thread.
<p>
This service atomically sets the cancelability type of the calling thread, and return its previous value at the address <em>oldtype_ptr</em>, if this thread is a Xenomai POSIX skin thread (i.e. was created with the <a class="el" href="group__posix__thread.html#ge6e819ed048e4c4a4ee96fa6f426852c" title="Create a thread.">pthread_create()</a> service).<p>
The cancelability type of a POSIX thread may be:<ul>
<li>PTHREAD_CANCEL_DEFERRED, meaning that cancellation requests are only handled in services which are cancellation points;</li><li>PTHREAD_CANCEL_ASYNCHRONOUS, meaning that cancellation requests are handled as soon as they are sent.</li></ul>
<p>
<dl compact><dt><b>Parameters:</b></dt><dd>
<table border="0" cellspacing="2" cellpadding="0">
<tr><td valign="top"></td><td valign="top"><em>type</em> </td><td>new cancelability type of the calling thread;</td></tr>
<tr><td valign="top"></td><td valign="top"><em>oldtype_ptr</em> </td><td>address where the old cancelability type will be stored on success.</td></tr>
</table>
</dl>
<dl class="return" compact><dt><b>Returns:</b></dt><dd>0 on success; <p>
an error number if:<ul>
<li>EINVAL, <em>type</em> is not a valid cancelability type;</li><li>EPERM, the caller context is invalid.</li></ul>
</dd></dl>
<dl class="user" compact><dt><b>Valid contexts:</b></dt><dd><ul>
<li>Xenomai POSIX skin kernel-space thread,</li><li>Xenomai POSIX skin user-space thread (switches to primary mode).</li></ul>
</dd></dl>
<dl class="see" compact><dt><b>See also:</b></dt><dd><a href="http://www.opengroup.org/onlinepubs/000095399/functions/pthread_setcanceltype.html">Specification.</a> </dd></dl>
<p>Referenced by <a class="el" href="src_2skins_2native_2cond_8c-source.html#l00065">rt_cond_wait()</a>, <a class="el" href="src_2skins_2native_2cond_8c-source.html#l00115">rt_cond_wait_until()</a>, <a class="el" href="src_2skins_2native_2intr_8c-source.html#l00044">rt_intr_wait()</a>, <a class="el" href="src_2skins_2native_2queue_8c-source.html#l00183">rt_queue_read()</a>, <a class="el" href="src_2skins_2native_2queue_8c-source.html#l00198">rt_queue_read_until()</a>, <a class="el" href="src_2skins_2native_2queue_8c-source.html#l00153">rt_queue_receive()</a>, <a class="el" href="src_2skins_2native_2queue_8c-source.html#l00168">rt_queue_receive_until()</a>, <a class="el" href="src_2skins_2native_2queue_8c-source.html#l00125">rt_queue_send()</a>, <a class="el" href="src_2skins_2native_2queue_8c-source.html#l00139">rt_queue_write()</a>, <a class="el" href="src_2skins_2native_2sem_8c-source.html#l00043">rt_sem_p()</a>, <a class="el" href="src_2skins_2native_2sem_8c-source.html#l00057">rt_sem_p_until()</a>, <a class="el" href="src_2skins_2native_2task_8c-source.html#l00399">rt_task_send()</a>, <a class="el" href="src_2skins_2native_2task_8c-source.html#l00180">rt_task_shadow()</a>, <a class="el" href="src_2skins_2native_2task_8c-source.html#l00314">rt_task_sleep()</a>, <a class="el" href="src_2skins_2native_2task_8c-source.html#l00327">rt_task_sleep_until()</a>, and <a class="el" href="src_2skins_2native_2task_8c-source.html#l00294">rt_task_wait_period()</a>.</p>
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<a class="anchor" name="gf1c95282ab2bea25f0888a19652cd41f"></a><!-- doxytag: member="cancel.c::pthread_testcancel" ref="gf1c95282ab2bea25f0888a19652cd41f" args="(void)" -->
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<td class="memname">void pthread_testcancel </td>
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<td class="paramtype">void </td>
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<p>
Test if a cancellation request is pending.
<p>
This function creates a cancellation point if the calling thread is a Xenomai POSIX skin thread (i.e. created with the <a class="el" href="group__posix__thread.html#ge6e819ed048e4c4a4ee96fa6f426852c" title="Create a thread.">pthread_create()</a> service).<p>
This function is a cancellation point. It has no effect if cancellation is disabled.<p>
<dl class="user" compact><dt><b>Valid contexts:</b></dt><dd><ul>
<li>Xenomai POSIX skin kernel-space thread,</li><li>Xenomai POSIX skin user-space thread (switches to primary mode).</li></ul>
</dd></dl>
<dl class="see" compact><dt><b>See also:</b></dt><dd><a href="http://www.opengroup.org/onlinepubs/000095399/functions/pthread_testcancel.html">Specification.</a> </dd></dl>
<p>Referenced by <a class="el" href="src_2skins_2native_2cond_8c-source.html#l00065">rt_cond_wait()</a>, and <a class="el" href="src_2skins_2native_2cond_8c-source.html#l00115">rt_cond_wait_until()</a>.</p>
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<hr size="1"><address style="text-align: right;"><small>Generated on Mon Aug 2 12:48:40 2010 for Xenomai API by
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