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><H1
><A
NAME="KERNEL-THREAD-DESTRUCTORS">Thread destructors</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN730"
></A
><H2
>Name</H2
>cyg_thread_add_destructor, cyg_thread_rem_destructor -- Call functions on thread termination</DIV
><DIV
CLASS="REFSYNOPSISDIV"
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><PRE
CLASS="FUNCSYNOPSISINFO"
>#include <cyg/kernel/kapi.h>
typedef void (*<SPAN
CLASS="TYPE"
>cyg_thread_destructor_fn</SPAN
>)(<SPAN
CLASS="TYPE"
>cyg_addrword_t</SPAN
>);
</PRE
></TD
></TR
></TABLE
><P
><CODE
><CODE
CLASS="FUNCDEF"
>cyg_bool_t cyg_thread_add_destructor</CODE
>(cyg_thread_destructor_fn fn, cyg_addrword_t data);</CODE
></P
><P
><CODE
><CODE
CLASS="FUNCDEF"
>cyg_bool_t cyg_thread_rem_destructor</CODE
>(cyg_thread_destructor_fn fn, cyg_addrword_t data);</CODE
></P
><P
></P
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN753"
></A
><H2
>Description</H2
><P
>These functions are provided for cases when an application requires a
function to be automatically called when a thread exits. This is often
useful when, for example, freeing up resources allocated by the thread.
</P
><P
>This support must be enabled with the configuration option
<TT
CLASS="VARNAME"
>CYGPKG_KERNEL_THREADS_DESTRUCTORS</TT
>. When enabled,
you may register a function of type
<SPAN
CLASS="TYPE"
>cyg_thread_destructor_fn</SPAN
> to be called on thread
termination using <TT
CLASS="FUNCTION"
>cyg_thread_add_destructor</TT
>. You
may also provide it with a piece of arbitrary information in the
<TT
CLASS="PARAMETER"
><I
>data</I
></TT
> argument which will be passed to the
destructor function <TT
CLASS="PARAMETER"
><I
>fn</I
></TT
> when the thread
terminates. If you no longer wish to call a function previous
registered with <TT
CLASS="FUNCTION"
>cyg_thread_add_destructor</TT
>, you
may call <TT
CLASS="FUNCTION"
>cyg_thread_rem_destructor</TT
> with the same
parameters used to register the destructor function. Both these
functions return <TT
CLASS="LITERAL"
>true</TT
> on success and
<TT
CLASS="LITERAL"
>false</TT
> on failure.
</P
><P
>By default, thread destructors are per-thread, which means that registering
a destructor function only registers that function for the current thread.
In other words, each thread has its own list of destructors.
Alternatively you may disable the configuration option
<TT
CLASS="VARNAME"
>CYGSEM_KERNEL_THREADS_DESTRUCTORS_PER_THREAD</TT
> in which
case any registered destructors will be run when <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>any</I
></SPAN
>
threads exit. In other words, the thread destructor list is global and all
threads have the same destructors.
</P
><P
>There is a limit to the number of destructors which may be registered,
which can be controlled with the
<TT
CLASS="VARNAME"
>CYGNUM_KERNEL_THREADS_DESTRUCTORS</TT
> configuration
option. Increasing this value will very slightly increase the amount
of memory in use, and when
<TT
CLASS="VARNAME"
>CYGSEM_KERNEL_THREADS_DESTRUCTORS_PER_THREAD</TT
> is
enabled, the amount of memory used per thread will increase. When the
limit has been reached, <TT
CLASS="FUNCTION"
>cyg_thread_add_destructor</TT
>
will return <TT
CLASS="LITERAL"
>false</TT
>.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="KERNEL-THREAD-DESTRUCTORS-CONTEXT"
></A
><H2
>Valid contexts</H2
><P
>When <TT
CLASS="VARNAME"
>CYGSEM_KERNEL_THREADS_DESTRUCTORS_PER_THREAD</TT
>
is enabled, these functions must only be called from a thread context
as they implicitly operate on the current thread. When
<TT
CLASS="VARNAME"
>CYGSEM_KERNEL_THREADS_DESTRUCTORS_PER_THREAD</TT
> is
disabled, these functions may be called from thread or DSR context,
or at initialization time.
</P
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