ld()</tt>
<DD>
Stops all threads which may access the garbage collected heap, other
than the caller.
<DT><TT>GC_start_world()</tt>
<DD>
Restart other threads.
<DT><TT>GC_push_all_stacks()</tt>
<DD>
Push the contents of all thread stacks (or at least of pointer-containing
regions in the thread stacks) onto the mark stack.
</dl>
These very often require that the garbage collector maintain its
own data structures to track active threads.
<P>
In addition, <TT>LOCK</tt> and <TT>UNLOCK</tt> must be implemented
in