I have a singleton in a web service that provides a collection and
self-updates it on a periodic basis:

doSelfUpdate()

 create temporary collection (time consuming)
 syncronize
   update temporary collection from current collection (fast)
   create temporary reference 'old' to current collection
   point current collection reference to temporary collection
 end syncronize
 do stuff with 'old' collection (time consuming)
 done

getCollection()
 synchronize
 just waiting on monitor
 end synchronize
 return collection
 done

It seems to me each thread accessing the getCollection method must
wait on the monitor every time it is accessed -- which is not what I
want.  I just want to open and close the gate for a few milliseconds
while the self-update is being done.  What do y'all think about
something like this:

boolean isBusy=false;

doSelfUpdate()
 create temporary collection
 isBusy=true;
   update temporary collection from current collection
   create temporary reference 'old' to current collection
   point current collection reference to temporary collection
 isBusy=false;
 do stuff with 'old' collection
 done

getCollection()
 maxWait=10000
 waited=0
 while(isBusy && waited <maxWait) {
    waited+=500
   if(waited>=MaxWait) log error;
    wait 500
    }
 return collection
 done

IMHO this means each thread consuming getCollection is a tiny bit
slower because it has a condition that must be tested, but as a group
they are not waiting in line for the monitor.  Is this right?