Software transactional memory is a promising programming model that adapts many concepts borrowed from the databases world to control concurrent accesses to main memory (RAM). This paper discusses how to support revertible operations, such as memory allocation and release, within software libraries that will be used in software memory transactional contexts. The proposal is based in the extension of the transaction life cycle state diagram with new states associated to the execution of user-defined handlers. The proposed approach is evaluated in terms of functionality and performance by way of a use case study and performance tests. Results demonstrate that the proposal and its current implementation are flexible, generic and efficient

Several decades ago, the file system was the container of choice for large bulks of related information, kept in hundreds of files, and relying on applications specifically created to handle them. These configurations weren't scalable and could easily become difficult to maintain, leading to the development and adoption of Database Management Systems (DBMS). These systems, capable of efficiently handling vast amounts of data, allowed heavy concurrency without requiring the programmer to deal with concurrency-control mechanisms, by encapsulating operations within transactions.
The properties of Transactions rapidly became an object of desire by many, and efforts to bring them to general-purpose programming environments began. In recent years there have been breakthroughs in bringing the transactional semantics to memory, using Software Transactional Memory (STM), providing abstractions to concurrency-control on the application-level. However, STM failed to meet some expectations, specially regarding I/O operations, forcing the abstraction to go deeper in the system: directly to the file system.
In this document we shall discuss file systems in general, their properties and common structure, although focusing in those with transactional or versioning capabilities. Later on, we will present our proposed enhancement of an existing Linux file system (Btrfs), in order to offer transactional semantics to applications, while detecting potential conflicts between concurrent flows of execution and reconciling their changes whenever possible.

Em caso de falha abrupta de um sistema, é imperativo garantir a consistência do Sistema de Ficheiros (SF). Actualmente existem várias solu{\c c}ões que visam garantir que tanto os dados como os metadados do SF se encontram num estado consistente, mas que não contemplam a garantia de consistência dos dados do ponto de vista das aplica{\c c}ões. Por exemplo, aplica{\c c}ões que pretendam alterar vários ficheiros de configura{\c c}ão terão de encontrar mecanismos para garantir que, ou todos os ficheiros são devidamente alterados, ou nenhum o é, evitando assim que numa situa{\c c}ão de falha o conteúdo dos ficheiros fique inconsistente. Do ponto de vista da aplica{\c c}ão, pode não ser simples implementar este comportamento sobre um SF t{\'ıpico; e pode também não ser razoável utilizar um Sistema de Gestão de Bases de Dados (SGBD), que oferece propriedades ACID. Neste artigo propomos, testamos e avaliamos uma integra{\c c}ão das propriedades ACID num SF. Partindo do suporte para snapshots do sistema de ficheiros Btrfs, oferece-se uma semântica transaccional às aplica{\c c}ões que operam sobre volumes (sub-árvores) do SF, sem comprometer a semântica POSIX do SF.