Hi JSR 277 experts, Below are some comments from Jeff Nisewanger and Karen Kinnear who are working on the ClassLoader API improvements for Java SE 7. If you are interested in contributing to the ClassLoader API improvements as a reviewer, you may contact Jeff and Karen at [EMAIL PROTECTED] and [EMAIL PROTECTED]
- Stanley -------- Original Message -------- Hi, Sun is working on the ClassLoader Deadlock fix. Our goal is to work closely with the community, of which the 277 EG contains key members, in coming up with small modifications to the current ClassLoader APIs to resolve that issue. As we've mentioned before, and Glyn even points out in his referenced blog, we did add a temporary risky unstable workaround which only really handles a small special case for WebSphere 6.1 which should be supplanted by the new mechanism as that becomes available. One of the key issues here is that a prerequisite for avoiding the ClassLoader deadlocks is that the JVM must not hold the ClassLoader Object lock when it calls out to LoadClass[Internal]. And presumably the lock must not be held when the custom class loader's loadClass() is called. As anyone who has written a custom class loader would immediately recognize, changing that underlying assumption is inherently risky. It is all too easy to break existing custom class loaders that were perhaps unknowingly relying on that lock to protect critical data and operations. Those are the kind of breakages that are extremely timing dependent and can pass many test cases and then unexpectedly fail in the field. I'm sure you all also remember when Unix user level libraries were converted to being MT-safe. We didn't get them all right the first time around. We don't want to put our customers in that position. So a part of the ClassLoader API modifications would be for class loaders to explicitly declare that they are safe for parallel class loading, both for multiple classes in the same class loader, and for multiple instances of the same class in the same class loader. I have been assuming that this would be the default for JSR 277, but we can work that issue in detail when we have a strawman ClassLoader API proposal. In the meantime, thank you very much to Adrian Brock for his classcircularity example. I will be studying it in detail. If any other EG member has a test scenario they would like to describe to us or even better they have a test case for, we would very much appreciate it. And if you are interested in contributing to the ClassLoader API improvements as a reviewer, please let us know. Thank you, Jeff Nisewanger & Karen Kinnear
