I'm curious what you find out about Commons Transactions. When I looked it over, it seemd to me designed with primitives for us to use to make our own transactions. I missed any ready-to-use code for this purpose.After 2 hours of copy/paste their FileResourceManager to use vfs.FileObject only I am able to do such thing:
// init phase
String tx1 = "tx1";
VFSResourceManager rsm = new VFSResourceManager(
VFS.getManager(),
"/home/im/tmp/tx/store", // <= root filesystem where the real stuff should happen on commit
"/home/im/tmp/tx/work", // <= work filesystem - could be different to store above
new PrintWriterLogger(new PrintWriter(System.err), "VFS", true),
true
);
rsm.start();
// start transaction
rsm.startTransaction(tx1);
// create file1
rsm.createResource(tx1, "dir1/file1.txt");
// create file2
rsm.createResource(tx1, "dir2/file1.txt");
// write into file1
OutputStream os = rsm.writeResource(tx1, "dir1/file1.txt");
os.write("test".getBytes());
os.close();
// delete file2
rsm.deleteResource(tx1, "dir2/file1.txt");
rsm.deleteResource(tx1, "dir2"); // <= dir2 has been created by the above createResource - now we have to remove it here manually.
// commit transaction
rsm.commitTransaction(tx1);
Now - whats missing in this example? .... right .... there is no "move" or "rename" operation.
Summary:
*) implement rename
*) implement something like listResource(tx) where we could get a list of all files in an directory - including/excluding those created/deleted within the transation.
Both need some more investigation to see how this could happen.
After experimenting a little bit it is fantastic to see who it prevents two simultan transactions to create the same file - in fact it isnt prevent - the second transaction just waits until the first has finished and then the second gains the lock.
So we get in-process locking for free.
The above code is just a start, but think of a file-object where the transactional logic is encapsulated and one can do whatever he wants - it will only be represented on the filesystem if commit() has been called.
FileObject foRootTransactional = VFS.getManager().beginTransaction(foRoot)
for (child .. foRootTransactional.getChildren())
{
child.delete();
}
VFS.getManager().commitTransaction(foRootTransactional);And maybe if your RamFS comes to reality we could use it as work-space e.g. if we know we handle only small transactions.
I am looking forward to read what you think about it.
If you would like to experiment a little bit follow the instructions at http://l3x.net/imwiki/Wiki.jsp?page=VfsStuff
--- Mario
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