Hi!
I know that closing the database is an old issue, but it seems I made things
hard for myself (no singletons, many Data instances can share the same database file, etc etc). It seems I have to choose between all bad ways of shutting down.
Bear with me and read a few of them, and tell me what you think. Am I just being paranoid?
The globalized option: Keep a global list of stuff to cleanup upon server shutdown. Call a method that cleans it up prior to a System.exit. Perhaps add a VM shutdown hook that does the same. My qualms about it: 1) Asides from the global list, it implies I must either make a global shutdown method or rely on a shutdown hook. Aren't globals supposed to be bad?
2) It prevents garbage collection.
The garbage option: Like the globalized option, but integrated with the garbage collector. The global cleanup list now consists of weak references so garbage collection is not hindered, and the class which holds the open database file gets to close it in its finalize method. The global shutdown method (or shutdown hook) still exists - but now it may have less to do because some cleanup has already been performed. My qualms about it: A) I am afraid junior programmers have lost their way by now.
B) I am afraid I am overdoing it.
The localized option: The database service offers a close method, and delegates that call to the data class, which delegates it onwards until the file is eventually closed. My qualms about it: I) Since in my design, many Data instances can share the same file, I end up having the Data class effectively maintaining a count of how many clients are using the file - that is, in some sense, doing the garbage collector's work.
II) To avoid unpredicable errors, every method in e.g. the Data class has to check that the close method has not been called (or does it?). Furthermore, these checks must be
thread safe (or must they?) - I guess you can boil it down to a "private volatile boolean closed", but still, isn't there a better way?
The ignorant option: Assume that the runtime will somehow manage things for you. Or be a bit more careful: Open the file in "rws" mode and close it in the finalizer and assume that takes care of the problem. My qualms about it: #) So far, I haven't managed to find documentation that guarantees this approach will work.
The smelly option: When the file-holding object is created, add a shutdown hook that will close the file. If the finalize method of the file-holding object is called, close the file there and remove the hook. My qualms about it: X) Hmm, it just has a bad smell - I have never before heard of anyone who has had to use shutdown hooks.
Thanks in advance!
[ March 30, 2004: Message edited by: Nicky Bodentien ]
[ March 30, 2004: Message edited by: Nicky Bodentien ]
[ March 30, 2004: Message edited by: Nicky Bodentien ]
