URL Rewriter: Large hiccups and possible OOM during reloading of url rewrite rules

public void doFilter(final ServletRequest request, final
ServletResponse response, final FilterChain chain) throws IOException,
ServletException {
// check if we loaded from repository, otherwise do nothing
if (!initialized) {
synchronized (lock)

{ fetchRules(); }

}
// check if we need to reload rules:
if (needsReloading())

{ fetchRules(); }

1) problem 1 : If after startup, directly 10 requests hit the site,
they all get halted on 'synchronized (lock)' ..... but they will ALL
call fetchRules in the end. Of course the code must be

if (!initialized) {
synchronized (lock) {
if (!initialized)

{ fetchRules(); }

}
}

note, initialized is correctly marked to be volatile.

2) problem 2 (Serious issue!): After a change in the repository for a
rewrite rule, needsReloading() returns true. The reload takes long for
say, more than 1000 rules. Once the model is reloaded,
needsReloading() returns false. However, every request before the
model is reloaded, triggers a reload as well. For 20.000 rules, I get
OOM after minutes. Ouch.

I will fix issue (1) and (2) in the url rewriter project, and for my
performance graph, try to be gentle to avoid stampeding herds pulling
down the entire application

Another problem is that during (re)building the in memory model, jcr
events can arrive setting needRefresh = true, which once the model is
reloaded is again set to needRefresh = false. In other words, events
that arrive during the building of the model are ignored, resulting in
possibly missing rules. For this make sure that

public void invalidate(final Event event)

{ needRefresh = true; }

becomes synchronized as well, thus

public synchronized void invalidate(final Event event) { needRefresh = true; }