A dead listener, say, ExecutionInit, stall ZK execution

If a listener, e.g., ExecutionInit, takes too long to execute or dead, the whole ZK execution will be stalled.

Reason:
In Configuration.java, we have codes like

synchronized (_evtInits) {
for (Iterator it = _evtInits.iterator(); it.hasNext();) {
...
EventThreadInit init =
(EventThreadInit)klass.newInstance();
init.prepare(comp, evt);
...

Thus, if prepare() is dead, no one is ever to enter synchronized (_evtInits)