Compiling first-order functions to session-typed parallel code

Abstract

Building correct and efficient message-passing parallel programs still poses many challenges. The incorrect use of message-passing constructs can introduce deadlocks, and a bad task decomposition will not achieve good speedups. Current approaches focus either on correctness or efficiency, but limited work has been done on ensuring both. In this paper, we propose a new parallel programming framework, PAlg, which is a first-order language with participant annotations that ensures deadlock-freedom by construction. PAlg programs are coupled with an abstraction of their communication structure, a global type from the theory of multiparty session types (MPST). This global type serves as an output for the programmer to assess the efficiency of their achieved parallelisation. PAlg is implemented as an EDSL in Haskell, from which we: 1. compile to low-level message-passing C code; 2. compile to sequential C code, or interpret as sequential Haskell functions; and, 3. infer the communication protocol followed by the compiled message-passing program. We use the properties of global types to perform message reordering optimisations to the compiled C code. We prove the extensional equivalence of the compiled code, as well as protocol compliance. We achieve linear speedups on a shared-memory 12-core machine, and a speedup of 16 on a 2-node, 24-core NUMA.