We present the TIC (Transactions with Isolation and Cooperation) model for concurrent programming. TIC adds to standard transactional memory the ability for a transaction to observe the effects of other threads at selected points. This allows transactions to cooperate, as well as to invoke nonrepeatable or irreversible operations, such as I/O. Cooperating transactions run the danger of exposing intermediate state and of having other threads change the transaction's state. The TIC model protects against unanticipated interference by having the type system keep track of all operations that may (transitively) violate the atomicity of a transaction and require the programmer to establish consistency at appropriate points. The result is a programming model that is both general and simple. We have used the TIC model to re-engineer existing lock-based applications including a substantial multi-threaded web mail server and a memory allocator with coarse-grained locking. Our experience confirms the features of the TIC model: It is convenient for the programmer, while maintaining the benefits of transactional memory.

The past three decades have seen the creation of several tools that extract, visualize, and manipulate graph-structured representations of program information. To facilitate interconnection and exchange of information between these tools, and to support the prototyping and development of new tools, it is desirable to have some generic support for the specification of graph transformations and exchanges between them.GENSET is a generic programmable tool for transformation of graph-structured data. The implementation of the GENSET system and the programming paradigm of its language are both based on the view of a directed graph as a binary relation. Rather than use traditional relational algebra to specify transformations, however, we opt instead for the more expressive class of flow equations. Flow equations-or, more generally, systems of simultaneous fixpoint equations-have seen fruitful applications in several areas, including data and control flow analysis, formal verification, and logic programming. In GENSET, they provide the fundamental construct for the programmer to use in defining new transformations.