/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, howeve