On the Behaviour of General-Purpose Applications on Cloud Storages

Managing data over cloud infrastructures raises novel challenges with respect to existing and well studied approaches such as ACID and long running transactions. One of the main requirements is to provide availability and partition tolerance in a scenario with replicas and distributed control. This comes at the price of a weaker consistency, usually called eventual consistency. These weak memory models have proved to be suitable in a number of scenarios, such as the analysis of large data with Map-Reduce. However, due to the widespread availability of cloud infrastructures, weak storages are used not only by specialised applications but also by general purpose applications. We provide a formal approach, based on process calculi, to reason about the behaviour of programs that rely on cloud stores. For instance, one can check that the composition of a process with a cloud store ensures `strong' properties through a wise usage of asynchronous message-passing

On Thin Air Reads: Towards an Event Structures Model of Relaxed Memory

To model relaxed memory, we propose confusion-free event structures over an alphabet with a justification relation. Executions are modeled by justified configurations, where every read event has a justifying write event. Justification alone is too weak a criterion, since it allows cycles of the kind that result in so-called thin-air reads. Acyclic justification forbids such cycles, but also invalidates event reorderings that result from compiler optimizations and dynamic instruction scheduling. We propose the notion of well-justification, based on a game-like model, which strikes a middle ground. We show that well-justified configurations satisfy the DRF theorem: in any data-race free program, all well-justified configurations are sequentially consistent. We also show that rely-guarantee reasoning is sound for well-justified configurations, but not for justified configurations. For example, well-justified configurations are type-safe. Well-justification allows many, but not all reorderings performed by relaxed memory. In particular, it fails to validate the commutation of independent reads. We discuss variations that may address these shortcomings

A Machine-Checked, Type-Safe Model of Java Concurrency : Language, Virtual Machine, Memory Model, and Verified Compiler

The Java programming language provides safety and security guarantees such as type safety and its security architecture. They distinguish it from other mainstream programming languages like C and C++. In this work, we develop a machine-checked model of concurrent Java and the Java memory model and investigate the impact of concurrency on these guarantees. From the formal model, we automatically obtain an executable verified compiler to bytecode and a validated virtual machine