2009/1/4 Nathan Beyer <[email protected]> > Could any of the IBM folks on the list get some advice from some class > loader experts? > > -Nathan >
Hi Nathan, from reading the description I can describe how Jikes RVM avoids this problem (I'm not an IBM VME expert and I've not run the test case to check that Jikes RVM passes it). In Jikes RVM we have two variants of all calls, ones to unresolved methods and ones to resolved methods. Unresolved calls are to classes whose initializer hasn't yet been run. If two threads are calling a static method the first will resolve it and in the process acquire a lock, the second thread must wait for the lock before it can attempt to resolve the method (at which point it will discover the method was resolved by the other thread and leave early). Checking for classes being resolved litters all of the class loader code, and we're slightly proactive in resolving in the case of reflected methods so that we needn't check for resolution when performing reflected method invocation (which is now pretty much unnecessary since [1] where we generate bytecodes at runtime to perform reflection). An aside, I wrote a paper where I use the class loader as a test case for optimizations based on stationary/immutable fields specified via constraints [2], this work specialized the class loader to handle the resolved case as a class is normally accessed when it is resolved (figures in the paper). Regards, Ian Rogers [1] http://icooolps.loria.fr/icooolps2008/Papers/ICOOOLPS2008_paper08_Rogers_Zhao_Watson_final.pdf [2] http://portal.acm.org/citation.cfm?id=1411746
