Randy Belknap wrote:
> >* Does the log() implementation write directly to an underlying file,
> > or does it just queue messages to an in-memory buffer that is
> > flushed asynchronously by a background thread?.
> >
>
> Craig,
>
> I've got an application that has to log some high level events (log in, document
>views, etc.) My appLog() method currently inserts these events directly into the
>Oracle database and is unsynchronized. I've been thinking about replacing this with
>a system like you describe above, but am not sure about the
>synchronization/performance issues. Do you have some recommendations?
>
> What I was thinking was to have the appLog() method add the events into a List (I'm
>using 1.1 collections) and then a timed process drain the List and write the events
>to the database.
>
> If I did it this way, would I have to synchronize adding elements to the List?
>Should the background process lock the List and copy it to a new List for processing?
>
> List tempList = listOfEvents; //listOfEvents is List used to log events
> listOfEvents = new ArrayList();
>
> Thanks,
>
> Randy
>
When using the Collections API, synchronization is definitely something needed. I
would code the event enqueuer like this:
List eventList = new ArrayLIst(); // Or whatever list type you want
synchronized (tempList) {
tempList.add(event);
}
For the dequeuer thread, lock-and-copy seems like a reasonable way to go. Then, you
can iterate through the copy without interference by threads queueing new events
during your output processing. I don't have the collections API stuff right at hand,
but it might have a clone() method you can use, instead of having to do it in a loop.
An alternative implementation would be to just dequeue one element at a time
(synchronized) and remove it from the list, then do the output. You'd need to be
careful which list implementation you chose, though.
Craig McClanahan
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