Operational semantics for signal handling

Signals are a lightweight form of interprocess communication in Unix. When a process receives a signal, the control flow is interrupted and a previously installed signal handler is run. Signal handling is reminiscent both of exception handling and concurrent interleaving of processes. In this paper, we investigate different approaches to formalizing signal handling in operational semantics, and compare them in a series of examples. We find the big-step style of operational semantics to be well suited to modelling signal handling. We integrate exception handling with our big-step semantics of signal handling, by adopting the exception convention as defined in the Definition of Standard ML. The semantics needs to capture the complex interactions between signal handling and exception handling.Comment: In Proceedings EXPRESS/SOS 2012, arXiv:1208.244

Semantics and logics for signals

In operating systems such as Unix, processes can interact via signals. Signal handling resembles both exception handling and concurrent interleaving of processes. The handlers can be installed dynamically by the main program, but signals arrive non-deterministically; therefore, a handler may interrupt a program at any point. However, the interleaving of actions is not symmetric, in that the handler interrupts the main program, but not conversely. This thesis presents operational semantics and program logic for an idealized form of signal handling. To make signal handling logically tractable, we define handling to be block-structured. To reason about the interleaving of signal handlers, we adopt the idea of binary relations on states from rely-guarantee logics, imposing rely conditions on handlers. Given the one-way interleaving of signal handlers, the logic is less symmetric than rely-guarantee. We combine signal and exception handlers in the same language to investigate their interactions, specifically whether a handler can run more than once or is linearly used. We prove soundness of the program logic relative to a big-step operational semantics for signal handling. Then, we introduce and discuss reentrancy in various domains. Finally, we present our work towards logic with Reentrancy Linear Type System