Robert Burrell Donkin ha scritto: > i've been observing sporadic exceptions in my fetchmail->sieve->IMAP. > the exceptions are thrown even though the mail filtering works fine > when the script is run offline. the majority of these exceptions have > been fixed by adding read/write locking to the torque mailbox. so, > i've been able to focus on the small number left. these don't appear > to be IMAP related. > > the usual symptom (for these remaining issues) is a failed check in > http://svn.apache.org/repos/asf/james/jsieve/trunk/src/main/java/org/apache/jsieve/commands/CommandStateManager.java. > i've been wondering recently whether the concurrency isn't quite > right in this class. these issues are hard to debug and tend to > require a lot of staring at the code. so hopefully, people will help > me out by lending an eye ball or two and then stating their opinions. > > 1 ThreadLocal is created lazily and is used without subclassing. > http://java.sun.com/j2se/1.5.0/docs/api/java/lang/ThreadLocal.html > recommends subclassing. > > 2 the instance is set to nulled on a reset. in the case of concurrent > threads, a reset in one thread may lead to loss of state in another. a > reset on the instance would prevent this. > > i think that it may better to eliminate the static per-thread > singleton manipulation methods and replace them with a ThreadLocal > subclass declared final. the reset would then be moved into the > instance. > > opinions?
I see the set/update/compute/reset/get/getBasic pattern applied there. This is a Steve signature ;-) . I admit I don't know the motivation behind that pattern and I don't know what are the advantages and problems caused by that pattern. I tend to remove most of them when I find it on my way because of code readability issues IMHO sacrificed with no specific advantage (but maybe it's my ignorance). I rarely used ThreadLocals in past but when I used it I referred to the way documented by Concurrent programming in Java. I don't have "synchronized" in the getInstance (that simply call the threadlocal.get) and the threadlocal is not subclassed (but a simple private static, like the one in CommandStateManager). That said I would probably try to simplify the pattern used in the class by splitting the threadlocal container by the CommandStateManager. Here we have a weird behavior where each instance contains another unused threadlocal creating a "new CommandStateManager();". Maybe it should be refactored so that the object containining the statuses (and setters/getters) is an inner static class and does not contain another ThreadLocal. Another issue I see with ThreadLocal usage is that this may conflict with SEDA based "users" of the library. I don't know the jSieve architecture but if it keep 1 status for each thread then we have to be sure you initialize and complete a full jSieve call within a single thread. Otherwise we would need a Memento pattern instead of the ThreadLocal so that the client could pass the current status at each call. Again I never used and I don't know jSieve codebase, so this is only a consideration based on reading few java source code. Stefano --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]