A concurrency-agnostic protocol for multi-paradigm concurrent debugging tools

Abstract

Today's complex software systems combine high-level concurrency models. Each model is used to solve a specific set of problems. Unfortunately, debuggers support only the lowlevel notions of threads and shared memory, forcing developers to reason about these notions instead of the high-level concurrency models they chose.This paper proposes a concurrency-agnostic debugger protocol that decouples the debugger from the concurrency models employed by the target application. As a result, the underlying language runtime can define custom breakpoints, stepping operations, and execution events for each concurrency model it supports, and a debugger can expose them without having to be specifically adapted.We evaluated the generality of the protocol by applying it to SOMns, a Newspeak implementation, which supports a diversity of concurrency models including communicating sequential processes, communicating event loops, threads and locks, fork/join parallelism, and software transactional memory. We implemented 21 breakpoints and 20 stepping operations for these concurrency models. For none of these, the debugger needed to be changed. Furthermore, we visualize all concurrent interactions independently of a specific concurrency model. To show that tooling for a specific concurrency model is possible, we visualize actor turns and message sends separately. This paper presents the Kómpos protocol, a concurrencyagnostic protocol to enable debuggers to support a wide range of concurrency models. Using the Kómpos protocol, we built the Kómpos debugger for online debugging of complex concurrent systems that combine communicating event loops (CEL) [Miller et al. 2005], communicating sequential processes (CSP) [Hoare 1978], software transactional memory (STM) [Harris et al. 2005], fork/join [Blumofe et al. 1995], and shared-memory threads and locks. Based on the concurrencyagnostic protocol, Kómpos supports a rich set of breakpoints for the various concurrency abstractions, a rich set of stepping semantics to explore program behavior, a generic visualization of interactions between concurrent entities, as well as an actor-specific visualization of turns and message sends. This evaluation shows that the Kómpos protocol is (1) general enough to support advanced debugger features for shared-memory and message-passing models, and (2) that it supports tools using the provided data independently of any concurrency model, while preserving the ability to build tools specific to a single model.Kómpos is a debugger for SOMns, a Newspeak implementation [Bracha et al. 2010] based on Truffle [Würthinger et al. 2012]. SOMns' debugger support is built on Truffle's tooling and debugger features [Seaton et al. 2014;Van De Vanter 2015]. SOMns supports the five aforementioned concurrency models and implements breakpoints, stepping, and a tracing mechanism for them. Because of the concurrency-agnostic design of the Kómpos protocol, the Kómpos debugger is independent from these concurrency models.The contributions of this paper are:

Efficient and deterministic record & replay for actor languages

“…Debugging support for the actor model so far focused either on breakpoint-based debuggers with support for actor-specific inspection, stepping operations, breakpoints, asynchronous stack traces, and visualizations [4,25], or it focused on postmortem debugging, e.g. Causeway [37], where a program's execution is analyzed after it crashed.…”

“…SOMns is an implementation of Newspeak [5] on top of the Truffle framework and the Graal just-in-time compiler [43]. Furthermore, we provide support for recording additional detailed information during replay executions, which can be used in the Kómpos debugger [25] for visualizations or post-mortem analyses.…”

Capturing High-level Nondeterminism in Concurrent Programs for Practical Concurrency Model Agnostic Record & Replay

“…While the semantics of the individual models differ, there are similarities in the structure of the concepts. In previous work, we presented a taxonomy of concurrency concepts for a concurrency-agnostic debugger protocol [24]. This provided inspiration for the identification of key concepts and sources of nondeterminism we employ in this work summarized in Table 1.…”

“…In prior work we have investigated online debugging of multi-paradigm concurrent programs for the Kómpos debugger protocol [24]. It allows language runtimes to define custom breakpoints and stepping operations for concurrency models without having to adapt a debugger.…”

A Study of Concurrency Bugs and Advanced Development Support for Actor-based Programs

“…Kómpos [40] is an online debugger for SOMns. For debugging actor-based programs, Kómpos provides a wide set of message-oriented breakpoints and stepping operations.…”