A way to have a timeout while waiting on a condition is needed

ECL provides this function, but it's currently unimplemented. In condition_variable.c:

cl_object
mp_condition_variable_timedwait(cl_object cv, cl_object lock, cl_object seconds)
{
        FEerror("Timed condition variables are not supported.", 0);
}

An implementation for this would be very useful.