On Fri, Dec 5, 2008 at 12:37 PM, Oliver Schoett <[EMAIL PROTECTED]> wrote: > Leon Rosenberg wrote: >> >> On Fri, Dec 5, 2008 at 9:50 AM, Oliver Schoett >> <[EMAIL PROTECTED]> wrote: >> >>> >>> Martin Gainty wrote: >>> >>>> >>>> so the solution is put all updates/inserts to the arraylist into a >>>> synchronized method? >>>> >>> >>> You must synchronize all read and write methods, because nothing may run >>> in >>> parallel with a write method, and so read methods must be prevented from >>> executing if a write method runs already. >>> >>> The only exception is if you can ensure that the ArrayList is read-only >>> at >>> some point in your program (e. g., after a setup phase). >>> >>> Arguing that the size() function cannot loop does not help, because the >>> size >>> function could be called internally in an infinite loop (this would be >>> visible in the call stack). >>> >> >> Oliver, >> I'm very sorry but i really don't see your point. >> The only possible need to synchronize access to ArrayList.size is when >> you a) access the list from different threads and b) need the result >> to be exact. Neither was the fact in my original post, in fact, as we >> already resolved it, the vm was getting out of old gen space and >> afterwards just behaving weird. >> > > Three points: > > (1) In the absence of call stack information, we do not know whether the > size() calls showing up in the thread dumps come from the application or are > internal calls from some other ArrayList function that may be in an infinite > loop.
The stack trace was sent to people who wanted it. > (2) That size() cannot loop may be a property of the current implementation; > it is not guaranteed by the API. Actually it is. * The <tt>size</tt>, <tt>isEmpty</tt>, <tt>get</tt>, <tt>set</tt>, * <tt>iterator</tt>, and <tt>listIterator</tt> operations run in constant * time. The <tt>add</tt> operation runs in <i>amortized constant time</i>, * that is, adding n elements requires O(n) time. All of the other operations * run in linear time (roughly speaking). The constant factor is low compared * to that for the <tt>LinkedList</tt> implementation.<p> > > (3) In general, when you query the size, you then want to do something > according to the value you got. Unless there is a synchronizaton block > around the size call and the subsequent action that guarantees that there > are no intervening changes to the ArrayList, the size call is useless, as > the ArrayList may change arbitrarily between the size call and the action. > Thus in general, even "harmless" query functions will appear inside > synchronized sections together with the actions that use the result value. > (The only exception I see is where the result value is just used for > information and does not control any action). You should consider using synchronized lists :-) (for example Vector). regards Leon --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
