To be a bit more positive and not just criticizing, this could probably be solved using a ThreadLocal [1] which would make the whole thing almost as handy as a normal static variable but thread-safe. But I've never done this myself, yet, so I can't talk out of experience. Just an additional 0.05 CHF.
[1] http://java.sun.com/j2se/1.4.2/docs/api/java/lang/ThreadLocal.html On 06.09.2004 22:01:27 Jeremias Maerki wrote: > Ok, the FOEventHandler is created in the FOTreeBuilder. One FO > TreeBuilder is instantiated per processing run. The FOEventHandler is > set on FONode's static variable during startDocument(). The > FOEventHandler keeps track of used fonts, number of pages, tracking IDs > etc. which are all relevant to one document run. > > Now imagine a situation where multiple processing runs occur and just > after the TreeBuilder sets the FOEventHandler on FONode in > startDocument() and continues layout, another thread starts another > processing run and runs through FOTreeBuilder.startDocument() before the > whole layout process of the first processing run is finished. The second > run will replace the FOEventHandler on FONode with a new one and the > first thread will suddenly work on a different FOEventHandler because > both threads access the same static variable. The behaviour will be > non-deterministic. > > Statics are often handy and seductive but are very dangerous in a > multi-threaded environment. FOP is expected to work this way as many > mails on fop-user prove. Statics are fine for constants and mostly ok > for singletons and a few other opportunities, but I made it a rule for > myself to be very catious when I think about using a static variable. I > try to avoid them whenever possible. > > On 06.09.2004 21:45:34 Glen Mazza wrote: > > Please elaborate. > > > > Jeremias Maerki wrote: > > > > >I'm sorry, Glen, but I think you will have to revisit that one. If I'm > > >not absolutely wrong, this will break multi-threading capabilities. > > > > > >On 06.09.2004 20:28:17 gmazza wrote: > > > > > > > > >>gmazza 2004/09/06 11:28:17 > > >> > > >> Modified: src/java/org/apache/fop/fo FONode.java FOTreeBuilder.java > > >> src/java/org/apache/fop/fo/pagination Root.java > > >> Log: > > >> Switched to a static FOInputHandler object for the FOTree instead of relying > > >> on recursion to get to the FOInputHandler object stored at pagination.Root. Jeremias Maerki
