Re: synchronize vs gate
On 04.06.2007 02:09, Tom Hawtin wrote:
I have a singleton in a web service that provides a collection and
self-updates it on a periodic basis:
create temporary collection (time consuming)
update temporary collection from current collection (fast)
create temporary reference 'old' to current collection
point current collection reference to temporary collection
do stuff with 'old' collection (time consuming)
just waiting on monitor
The obvious thing to do (from Java 1.5 spec, and 1.4 implementation) is
to make the reference to the collection volatile. Keep the lock in
doSelfUpdate, but not getCollection. Alternatively just use
Yet another alternative would be to use a ReadWriteLock that is held
during update of the reference only and use an immutable collection.
This of course works best if it is made sure through other means that
there is just one updater at a time - although two concurrent updaters
might only cost additional CPU. The logic should still work, you only
get two (or n) updates of the reference in a short period of time. If
the update process itself needs additional synchronization that can be
either provided by another Lock or different logic. Difficult to
speculate without knowing more detail...
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