Buster wrote:

I'm looking for an STL-like library that would let me do something like the following:

tp::database data; tp::map map1(data); tp::list<float> list1(data);

...

tp::transaction t; map1.start_transaction(t); list1.start_transaction(t);

map1[5] = "hello"; // does NOT commit to container or database list1.push_back(1.0); // does NOT commit either t.commit(); // Finally commits to container and database. // Without this call, t would call rollback // in destructor.

Does anyone know of such a library ? If not, I guess I'll have to do some writing.

If I do write it, it seems that using boost serialization would save a lot of the work. But I've looked at it and it seems to be missing a couple things I need. For one, it seems to require that you serialize the entire container each time you change one element. Perhaps I'm wrong ?

The approach I use is to use Berkeley DB for transactional persistence of each element/object in the database, and boost::serialization for converting C++ objects to and from the array of bytes that is required by Berkeley DB. That is, I serialize at the granularity of individuals objects in the database, rather than serializing the whole database contents in one go.

The other problem is that I don't see anything related to transactions within the library. This may even prevent me from using the library to implement the actual serialization of each element, as I wouldn't be able to gurantee that the data was NOT written.

I serialize an object to an in-memory byte vector first before saving to the database, so that (along with Berkeley DB) guarantees all-or-nothing (i.e. atomic) changes to the database.

Unless one can hook up transactional archives to boost serialization ?

Any advice or pointers would be greatly appreciated.

On 15/12/05, Buster wrote:

map1[5] = "hello"; // does NOT commit to container or database list1.push_back(1.0); // does NOT commit either t.commit(); // Finally commits to container and database. // Without this call, t would call rollback // in destructor.

http://www.cuj.com/documents/s=8000/cujcexp1812alexandr/alexandr.htm The scopeguard trick will work in any case where you have a rollback function that is nofail -- such as erase in a map or pop_back in a list. For more complex tasks you'll need a more complex solution, but ScopeGuard is quite simple and elegant for many. I wrote an implementation you're free to use or imitate or whatever: http://www.uploadthis.co.uk/uploads/me22/guard.hpp - Scott McMurray