Efficient Synthesis for Concurrency by Semantics-Preserving Transformations

Abstract

We develop program synthesis techniques that can help programmers fix concurrency-related bugs. We make two new contributions to synthesis for concurrency, the first improving the efficiency of the synthesized code, and the second improving the efficiency of the synthesis procedure itself. The first contribution is to have the synthesis procedure explore a variety of (sequential) semantics-preserving program transformations. Classically, only one such transformation has been considered, namely, the insertion of synchronization primitives (such as locks). Based on common manual bug-fixing techniques used by Linux device-driver developers, we explore additional, more efficient transformations, such as the reordering of independent instructions. The second contribution is to speed up the counterexample-guided removal of concurrency bugs within the synthesis procedure by considering partial-order traces (instead of linear traces) as counterexamples. A partial-order error trace represents a set of linear (interleaved) traces of a concurrent program all of which lead to the same error. By eliminating a partial-order error trace, we eliminate in a single iteration of the synthesis procedure all linearizations of the partial-order trace. We evaluated our techniques on several simplified examples of real concurrency bugs that occurred in Linux device drivers.

From Non-preemptive to Preemptive Scheduling Using Synchronization Synthesis

“…Program synthesis for concurrency aims to mitigate this complexity by synthesizing synchronization code automatically [5,6,9,15]. However, specifying the programmer's intent may be a challenge in itself.…”

Succinct Representation of Concurrent Trace Sets

“…Sets of concurrent traces containing permutations of events from a given concurrent trace are useful for predictive analysis (e.g., [24,34,35,41]) and synchronization synthesis (e.g., [8,9]) of sharedmemory concurrent programs. Most approaches using such trace sets are restricted to specific aspects of reasoning about concurrent programs such as data race detection [24,34], detection of safety violations [35,41] and fixing assertion failures [8,9].…”

“…Most approaches using such trace sets are restricted to specific aspects of reasoning about concurrent programs such as data race detection [24,34], detection of safety violations [35,41] and fixing assertion failures [8,9]. Moreover, the representations of trace sets and exploration strategies used in some of these approaches [8,9,35]) underapproximate the target trace sets. In this paper, we present a succinct, complete representation of such concurrent trace sets, which can drive diverse verification, fault localization, repair, and synthesis techniques for concurrent programs.…”

“…Some representations may be more expressive or useful for reasoning about concurrent programs than others. A candidate representation that has been used for certain trace sets is a partial order over events [8,9,41]. The neighbourhood of a trace, as defined above, can also be represented as a partial order.…”

“…Case Study: Synchronization synthesis. Shared-memory concurrent programs are excellent targets for automated program completion, in particular, for synthesis of missing synchronization [8,9,13,30,39]. We present a novel algorithm that uses ϕG to synthesize synchronization for eliminating the bad neighbourhood of τ .…”