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><H1
><A
NAME="KERNEL-THREAD-TERMINATION"
></A
>Thread termination</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN581"
></A
><H2
>Name</H2
>cyg_thread_exit, cyg_thread_kill, cyg_thread_delete&nbsp;--&nbsp;Allow threads to terminate</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN586"
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><H2
>Synopsis</H2
><DIV
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><PRE
CLASS="FUNCSYNOPSISINFO"
>#include &lt;cyg/kernel/kapi.h&gt;
        </PRE
></TD
></TR
></TABLE
><P
><CODE
><CODE
CLASS="FUNCDEF"
>void cyg_thread_exit</CODE
>(void);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>void cyg_thread_kill</CODE
>(cyg_handle_t thread);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>cyg_bool_t cyg_thread_delete</CODE
>(cyg_handle_t thread);</CODE
></P
><P
></P
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN603"
></A
><H2
>Description</H2
><P
>In many embedded systems the various threads are allocated statically,
created during initialization, and never need to terminate. This
avoids any need for dynamic memory allocation or other resource
management facilities. However if a given application does have a
requirement that some threads be created dynamically, must terminate,
and their resources such as the stack be reclaimed, then the kernel
provides the functions <CODE
CLASS="FUNCTION"
>cyg_thread_exit</CODE
>,
<CODE
CLASS="FUNCTION"
>cyg_thread_kill</CODE
>, and
<CODE
CLASS="FUNCTION"
>cyg_thread_delete</CODE
>.
      </P
><P
><CODE
CLASS="FUNCTION"
>cyg_thread_exit</CODE
> allows a thread to terminate
itself, thus ensuring that it will not be run again by the scheduler.
However the <CODE
CLASS="STRUCTNAME"
>cyg_thread</CODE
> data structure passed
to <CODE
CLASS="FUNCTION"
>cyg_thread_create</CODE
> remains in use, and the
handle returned by <CODE
CLASS="FUNCTION"
>cyg_thread_create</CODE
> remains
valid. This allows other threads to perform certain operations on the
terminated thread, for example to determine its stack usage via
<CODE
CLASS="FUNCTION"
>cyg_thread_measure_stack_usage</CODE
>. When the handle
and <CODE
CLASS="STRUCTNAME"
>cyg_thread</CODE
> structure are no longer
required, <CODE
CLASS="FUNCTION"
>cyg_thread_delete</CODE
> should be called to
release these resources. If the stack was dynamically allocated then
this should not be freed until after the call to
<CODE
CLASS="FUNCTION"
>cyg_thread_delete</CODE
>.
      </P
><P
>Alternatively, one thread may use <CODE
CLASS="FUNCTION"
>cyg_thread_kill</CODE
>
on another This has much the same effect as the affected thread
calling <CODE
CLASS="FUNCTION"
>cyg_thread_exit</CODE
>. However killing a thread
is generally rather dangerous because no attempt is made to unlock any
synchronization primitives currently owned by that thread or release
any other resources that thread may have claimed. Therefore use of
this function should be avoided, and
<CODE
CLASS="FUNCTION"
>cyg_thread_exit</CODE
> is preferred.
<CODE
CLASS="FUNCTION"
>cyg_thread_kill</CODE
> cannot be used by a thread to
kill itself.
      </P
><P
><CODE
CLASS="FUNCTION"
>cyg_thread_delete</CODE
> should be used on a thread
after it has exited and is no longer required. After this call the
thread handle is no longer valid, and both the
<CODE
CLASS="STRUCTNAME"
>cyg_thread</CODE
> structure and the thread stack can
be re-used or freed. If <CODE
CLASS="FUNCTION"
>cyg_thread_delete</CODE
> is
invoked on a thread that is still running then there is an implicit
call to <CODE
CLASS="FUNCTION"
>cyg_thread_kill</CODE
>. This function returns
<TT
CLASS="LITERAL"
>true</TT
> if the delete was successful, and
<TT
CLASS="LITERAL"
>false</TT
> if the delete did not happen. The delete
may not happen for example if the thread being destroyed is a lower
priority thread than the running thread, and will thus not wake up
in order to exit until it is rescheduled.
      </P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="KERNEL-THREAD-TERMINATION-CONTEXT"
></A
><H2
>Valid contexts</H2
><P
><CODE
CLASS="FUNCTION"
>cyg_thread_exit</CODE
>,
<CODE
CLASS="FUNCTION"
>cyg_thread_kill</CODE
> and
<CODE
CLASS="FUNCTION"
>cyg_thread_delete</CODE
> can only be called from thread
context. 
      </P
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