Safety Guarantees from Explicit Resource Management

We present a language and a program analysis that certifies the safe use of flexible resource management idioms, in particular advance reservation or “block booking” of costly resources. This builds on previous work with resource managers that carry out runtime safety checks, by showing how to assist these with compile-time checks. We give a small ANF-style language with explicit resource managers, and introduce a type and effect system that captures their runtime behaviour. In this setting, we identify a notion of dynamic safety for running code, and show that dynamically safe code may be executed without runtime checks. We show a similar static safety property for type-safe code, and prove that static safety implies dynamic safety. The consequence is that typechecked code can be executed without runtime instrumentation, and is guaranteed to make only appropriate use of resources.