May-happen-in-parallel analysis of X10 programs

Abstract

X10 is a modern object-oriented programming language designed for high performance, high productivity programming of parallel and multi-core computer systems. Compared to the lower-level thread-based concurrency model in the Java TM language, X10 has higher-level concurrency constructs such as async, atomic and finish built into the language to simplify creation, analysis and optimization of parallel programs. In this paper, we introduce a new algorithm for May-Happen-in-Parallel (MHP) analysis of X10 programs. The analysis algorithm is based on simple path traversals in the Program Structure Tree, and does not rely on pointer alias analysis of thread objects as in MHP analysis for Java programs. We introduce a more precise definition of the MHP relation than in past work by adding condition vectors that identify execution instances for which the MHP relation holds, instead of just returning a single true/false value for all pairs of executing instances. Further, MHP analysis is refined in our approach by using the observation that two statement instances which occur in atomic sections that execute at the same X10 place must have MHP = false. We expect that our MHP analysis algorithm will be applicable to any language that adopts the core concepts of places, async, finish, and atomic sections from the X10 programming model. We also believe that this approach offers the best of two worlds to programmers and parallel programming tools -higher-level abstractions of concurrency coupled with simple and efficient analysis algorithms.

Efficient May Happen in Parallel Analysis for Async-Finish Parallelism

“…In particular, the decision procedures in [19,19,8] weren't applied to realistic benchmarks. Instead, most previous papers on practical MHP analysis present static analyses that give conservative, approximate answers to the MHP computation problem [7,13,15,16,12,3,1,11]. The relationship between the approximate analyses and the theoretically optimal algorithms is unclear; if the theoretically optimal algorithms are also practically efficient, then that would make research into approximate analyses moot.…”

Coordinating Phased Activities while Maintaining Progress

“…FX10 is suited for inter-procedural analysis through type inference and includes a formal proof of a fragment of the deadlock theorem stated by Saraswat and Jagadeesan. The type system used to identify may-happen-parallelism is further explored in [2]. Other formal studies on fork/join semantics include [1,4].…”

Communication Optimizations for Distributed-Memory X10 Programs

“…Objects residing in one place may contain references to objects residing in other places. However, X10 enforces a strong locality property: it is not permissible to access an object's mutable state through a remote reference to that object 1 . Therefore computations must sometimes "shift" from one place to another to access the data they need.…”

“…A new activity is created by the statement async S. To synchronize activities, X10 provides the statement finish S. An activity that executes a finish statement will not execute the statement 1 The 1.7, 2.0, and 2.1 versions of X10 have had slightly different distributed object models, but this fundamental locality property is true of all three versions of the language. Mutable state can only be accessed in its home location.…”