Causal-Consistent Debugging of Distributed Erlang

The main purpose of this work is to study the reversibility in a concurrent and distributed environment. Reversing the execution of a program in such environment is not straightforward, indeed in order to undo a step performed by one of the, potentially many, processes of the system one has to make sure that also all of its consequences, if any, have been undone beforehand. This notion is usually referred to as causal consistency. Here, we study reversibility in the context of the Erlang language. In order to reverse the execution of a concurrent and distributed erlang program we define a forward semantics which, at each step performed by the program, stores in an external device, called history, auxiliary pieces of information that later on can be used to undo the step. In addition to the forward semantics we also develop a backward semantics and a rollback semantics, the former tells how and when we can undo a step while the latter allows us to undo several steps in an automatic manner. Lastly, we present a proof-of-concept implementation of a debugger able to reverse the execution of a concurrent and distributed program written in Erlang.