Gadara nets: Modeling and analyzing lock allocation for deadlock avoidance in multithreaded software

IFAC Proceedings Volumes

Liao

et al. 2010

Self Cite

Abstract:We discuss our experience in the Gadara project, whose objective is to control the execution of software to avoid potential failures using discrete-event control techniques. We summarize our accomplishments so far and discuss future challenges. After initial work on safety of workflow scripts via supervisory control techniques, we have focused our efforts on deadlock avoidance in multithreaded C programs that use locking primitives to control access to shared data. We describe how we automatically construct automata models of workflows and Petri net models of concurrent programs. In the case of multithreaded C programs, the resulting models characterize a new class of resource-allocation Petri nets called Gadara nets. These nets enjoy structural properties that facilitate the synthesis of liveness-enforcing control policies that are maximally-permissive. We describe our strategy for run-time implementation of these control policies, especially by a technique known as code instrumentation. It is hoped that the lessons learned so far in the Gadara project will be useful in other application areas and will suggest avenues for future theoretical investigations.

Section: Introductionmentioning

confidence: 75%

Supervisory Control of Software Execution for Failure Avoidance: Experience from the Gadara Project

Yin

IFAC Proceedings Volumes

Liao

et al. 2010

Self Cite

“…This challenge is especially problematic for Gadara, whose models must have the semiflow property [32]. Intuitively, the semiflow property means that a mutex acquired by a thread should be released later in the model.…”

Section: Infeasible Pathmentioning

confidence: 99%

Practical lock/unlock pairing for concurrent programs

Proceedings of the 2013 IEEE/ACM International Symposium on Code Generation and Optimization (CGO)

Kelly

Wang

et al. 2013

In the multicore era, developers face increasing pressure to parallelize their programs. However, building correct and efficient concurrent programs is substantially more difficult than building sequential ones. To address the multicore challenge, numerous tools have been developed to assist multithreaded programmers, including static and dynamic bug detectors, automated bug fixers, and optimization tools. Many of these tools rely on or benefit from the precise identification of critical sections, i.e., sections where the thread of execution holds at least one lock. For languages where critical sections are not lexically scoped, e.g., C/C++, static analysis often fails to pair up lock and unlock calls correctly.In this paper, we propose a practical lock/unlock pairing mechanism that combines static analysis with dynamic instrumentation to identify critical sections in POSIX multithreaded C/C++ programs. Our method first applies a conservative inter-procedural path-sensitive dataflow analysis to pair up all lock and unlock calls. When the static analysis fails, our method makes assumptions about the pairing using common heuristics. These assumptions are checked at runtime using lightweight instrumentation. Our experiments show that only one out of 891 lock/unlock pairs violates our assumptions at runtime and the instrumentation imposes negligible overhead of 3.34% at most, for large open-source server programs. Overall, our mechanism can pair up 98.2% of all locks including 7.1% of them paired speculatively.

“…Next we show that MPLE control through monitor places is always feasible in Gadara nets. Note that such a property does not always hold in general for other classes of nets; see (Wang et al, 2009b) for a counterexample. We first establish a general property that in Gadara nets, any set of reachable markings can always be separated from the rest through a set of linear inequalities, so that the SBPI technique can be used to synthesize monitor places to enforce such a separation.…”

Section: Linear Separability and Mple Control Of Gadara Netsmentioning

confidence: 99%

“…We present some examples of deadlocks from real-world software in Section 6, and conclude in Section 7. A preliminary version of some of the results in Sections 3 and 4 appears in (Wang et al, 2009b); a preliminary version of some of the results in Sections 5.2 and 5.3 appears in (Liao et al, 2011).…”

Section: Remarkmentioning

confidence: 99%

See 1 more Smart Citation

Concurrency bugs in multithreaded software: modeling and analysis using Petri nets

Liao

Yin

Discrete Event Dyn Syst

et al. 2012

Self Cite

In this paper, we apply discrete-event system techniques to model and analyze the execution of concurrent software. The problem of interest is deadlock avoidance in shared-memory multithreaded programs. We employ Petri nets to systematically model multithreaded programs with lock acquisition and release operations. We define a new class of Petri nets, called Gadara nets, that arises from this modeling process. We investigate a set of important properties of Gadara nets, such as liveness, reversibility, and linear separability. We propose efficient algorithms for the verification of liveness of Gadara nets, and report experimental results on their performance. We also present modeling examples of real-world programs. The results in this paper lay the foundations for the development of effective control synthesis algorithms for Gadara nets.