Hi Aaron!
On 6/24/05, Aaron Hamid <[EMAIL PROTECTED]> wrote:
> Hi all,
>
> I suspect I just reimplemented FileResourceManager, because I was not aware
> of it until recently (despite using the
> org.apache.commons.transaction.locking package). Basically I created a
> hierarchical Node interface, with operations like: children() and read(),
> which implicitly obtain a readlock; write(), which upgrades to a write lock;
> and close() which releases the locks.
>
> First, I'm wondering if there is a way to list a directory through the API,
> which itself requires a read lock, or whether I must explicitly obtain the
> lock, and then perform the listing externally (which is cumbersome).
The FileResourceManager is more low level than your approach. It does
not have the notion of hierarchichal data and thus no idea of
children.
> Also, I'm curious as to the significance of the "owner" parameter to the lock
> API. For instance, I keep lock objects as a member field of Node
> implementations, using the unique path as a resource id:
The "owner" is whatever object owns, i.e. holds, the lock. This can
e.g. be a thread, a process, a transaction, an application or
whatever. In "normal" Java locking this would be the thread.
> public class NodeImpl {
> private ReadWriteLock lock;
> private Node parent;
> public NodeImpl(Node parent, Path path, Store store) {
> lock = new ReadWriteLock(new StorePath(store, path), null);
> }
> public void open() {
> // should I send 'this' as owner?
> lock.acquireRead(this, Long.MAX_VALUE);
> }
> public void openForWriting() {
> // should I send 'this' as owner?
> lock.acquireWrite(this, Long.MAX_VALUE);
> }
> public void write() {
> parent.openForWriting();
> this.openForWriting();
> // .. do some writing ..
> }
> public void close() {
> lock.release();
> }
> }
>
> Now...what should the value of the "owner" object be? Should it naively be
> the 'this' object? Or should it be the Thread.currentThread(), or is it
> completely irrelevant and only for informational purposes? As you can see,
> to perform any writing, I must also lock the parent node (for instance, if
> the write creates a new file...we can't allow reads/listings to be
> happening). However, the parent node, in this implementation, will obtain
> the lock with an owner value of itself. Now, I intend Node usage to only be
> single-threaded anyway (the strategy being other threads would obtain a
> distinct node object, and not share node objects accross threads)...but in
> any case, is this still legitimate, or should I be obtaining the parent lock
> with some /other/ value of owner? If I used distinct owners with that
> prevent the child not from acquiring the lock, even though it is in its own
> thread? The semantics of "owner" don't seem to be very well documented.
I thought the notion of an "owner" was rahter obvious. Anyway, if you
have a single threaded application, why use locking?
Oliver
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