Concurrent libraries with foresight

Abstract

Linearizable libraries provide operations that appear to execute atomically. Clients, however, may need to execute a sequence of operations (a composite operation) atomically. We consider the problem of extending a linearizable library to support arbitrary atomic composite operations by clients. We introduce a novel approach in which the concurrent library ensures atomicity of composite operations by exploiting information (foresight) provided by its clients. We use a correctness condition, based on a notion of dynamic right-movers, that guarantees that composite operations execute atomically without deadlocks, and without using rollbacks. We present a static analysis to infer the foresight information required by our approach, allowing a compiler to automatically insert the foresight information into the client. This relieves the client programmer of this burden and simplifies writing client code. We present a generic technique for extending the library implementation to realize foresight-based synchronization. This technique is used to implement a general-purpose Java library for Map data structures -- the library permits composite operations to simultaneously work with multiple instances of Map data structures. We use the Maps library and the static analysis to enforce atomicity of a wide selection of real-life Java composite operations. Our experiments indicate that our approach enables realizing efficient and scalable synchronization for real-life composite operations.