Yes, that's what I had in mind.  Routine `eraise' (I assume everything goes
through this routine to raise an exception) could call EIF_ENTER_EIFFEL at
the beginning, then lock and unlock `eif_gc_mutex' to ensure synchronization
but only if multithreaded.  In other words, at beginning of `eraise' add:

   EIF_ENTER_EIFFEL;
   GC_THREAD_PROTECT(EIF_GC_MUTEX_LOCK);
   GC_THREAD_PROTECT(EIF_GC_MUTEX_UNLOCK);

The disadvantage is you have to lock and unlock the mutex whenever an
exception is raised.  So perhaps the above 3 lines should be done only
if the thread GC status is not already EIF_THREAD_RUNNING.  Not sure if
`eraise' can be called when thread GC status is EIF_THREAD_GC_RUNNING
or what should be executed in that case.

Seems right, but my brain is a bit fuzzy after a 7 day backpacking trip.