Guarantee Deadlock Freedom Research Articles

Intrinsically Typed Sessions with Callbacks (Functional Pearl)

All formalizations of session types rely on linear types for soundness as session-typed communication channels must change their type at every operation. Embedded language implementations of session types follow suit. They either rely on clever typing constructions to guarantee linearity statically, or on run-time checks that approximate linearity. We present a new language-embedded implementation of session types, which is inspired by the inversion-of-control design principle. With our approach, all application programs are intrinsically session-typed and unable to break linearity by construction. Our design relies on a tiny encapsulated library, for which linearity remains a proof obligation that can be discharged once and for all when the library is built. We demonstrate that our proposed design extends to a wide range of features of session type systems: branching, recursion, multichannel and higher-order sessions, as well as context-free sessions. The multichannel extension provides an embedded implementation of session types which guarantees deadlock freedom by construction. The development reported in this paper is fully backed by type-checked Agda code.

Pirouette: higher-order typed functional choreographies

We present Pirouette, a language for typed higher-order functional choreographic programming. Pirouette offers programmers the ability to write a centralized functional program and compile it via endpoint projection into programs for each node in a distributed system. Moreover, Pirouette is defined generically over a (local) language of messages, and lifts guarantees about the message type system to its own. Message type soundness also guarantees deadlock freedom. All of our results are verified in Coq.

Comparing type systems for deadlock freedom

Message-passing software systems exhibit non-trivial forms of concurrency and distribution; they are expected to follow intended protocols among communicating services, but also to never “get stuck”. This intuitive requirement has been expressed by liveness properties such as progress or (dead)lock freedom and various type systems ensure these properties for concurrent processes. Unfortunately, very little is known about the precise relationship between these type systems and the classes of typed processes they induce.This paper puts forward the first comparative study of different type systems for message-passing processes that guarantee deadlock freedom. We compare two classes of deadlock-free typed processes, here denoted L and K. The class L stands out for its canonicity: it results from Curry-Howard interpretations of classical linear logic propositions as session types. The class K, obtained by encoding session types into Kobayashi's linear types with usages, includes processes not typable in other type systems. We show that L is strictly included in K, and identify the precise conditions under which they coincide. We also provide two type-preserving translations of processes in K into processes in L.

Multicast-enabled network-on-chip routers leveraging partitioned allocation and switching

Multicast on-chip communication is encountered in various cache-coherence protocols targeting multi-core processors, and its pervasiveness is increasing due to the proliferation of machine learning accelerators. In-network handling of multicast traffic imposes additional switching-level restrictions to guarantee deadlock freedom, while it stresses the allocation efficiency of Network-on-Chip (NoC) routers. In this work, we propose a novel partitioned NoC router microarchitecture, called SmartFork, which employs a versatile and cost-efficient multicast packet replication scheme that allows the design of high-throughput and low-cost NoCs. The design is adapted to the average branch splitting observed in real-world multicast routing algorithms. Compared to state-of-the-art NoC multicast approaches, SmartFork is demonstrated to yield high performance in terms of latency and throughput, while still offering a cost-effective implementation.

Head‐of‐line blocking avoidance in Slim Fly networks using deadlock‐free non‐minimal and adaptive routing

SummaryInterconnection network performance is a key issue in HPC systems and datacenters, especially as their number of end nodes grows, to cope with application needs. The network topology and the routing algorithm are important factors for performance and cost. Topologies such as fat‐tree or Dragonfly were proposed to maximize network performance while reducing network resources. One of the most promising topologies is Slim Fly, which offers high network bandwidth assuring low network diameter. However, adversarial traffic and/or congestion situations may degrade Slim Fly's performance dramatically. Non‐minimal routings, such as Valiant or UGAL, can mitigate the former problem while queuing schemes can handle the latter one. In this paper, we proposed a combined mechanism to provide Slim Fly network with both non‐minimal routing and queuing schemes by using several virtual networks to guarantee deadlock freedom. Each virtual network consists of a set of virtual channels to store packets separately according to a mapping policy. This diminishes the interaction among traffic flows, thus reducing head‐of‐line blocking. The results obtained from a simulation‐based evaluation show that our proposal enhances the performance in all the traffic cases, in contrast to other mechanisms whose performance drops in certain scenarios.

Deadlock avoidance in parallel programs with futures: why parallel tasks should not wait for strangers

Futures are an elegant approach to expressing parallelism in functional programs. However, combining futures with imperative programming (as in C++ or in Java) can lead to pernicious bugs in the form of data races and deadlocks, as a consequence of uncontrolled data flow through mutable shared memory. In this paper we introduce the Known Joins (KJ) property for parallel programs with futures, and relate it to the Deadlock Freedom (DF) and the Data-Race Freedom (DRF) properties. Our paper offers two key theoretical results: 1) DRF implies KJ, and 2) KJ implies DF. These results show that data-race freedom is sufficient to guarantee deadlock freedom in programs with futures that only manipulate unsynchronized shared variables. To the best of our knowledge, these are the first theoretical results to establish sufficient conditions for deadlock freedom in imperative parallel programs with futures, and to characterize the subset of data races that can trigger deadlocks (those that violate the KJ property). From result 2), we developed a tool that avoids deadlocks in linear time and space when KJ holds, i.e., when there are no data races among references to futures. When KJ fails, the tool reports the data race and optionally falls back to a standard deadlock avoidance algorithm by cycle detection. Our tool verified a dataset of ∼2,300 student’s homework solutions and found one deadlocked program. The performance results obtained from our tool are very encouraging: a maximum slowdown of 1.06× on a 16-core machine, always outperforming deadlock avoidance via cycle-detection. Proofs of the two main results were formalized using the Coq proof assistant.

Foreword to the special issue on networked system security and efficiency

Foreword to the special issue on networked system security and efficiency

XOR-based HoL-blocking reduction routing mechanisms for direct networks

Abstract Routing is a key design parameter in the interconnection network of large parallel computers . Routing algorithms are classified into two different categories depending on the number of routing options available for each source–destination pair: deterministic (there is one path available) and adaptive (there are several ones). Adaptive routing has two opposed effects on network performance. On one hand, it provides routing flexibility that may help on avoiding a congested network area, thus improving network performance. On the other hand, it also may increase the Head-of-Line blocking effect due to more destination nodes sharing the port queues. Usually, adaptive routing uses virtual channels to provide routing flexibility and to guarantee deadlock freedom. Deterministic routing is simpler, which implies lower routing delay and it introduces less Head-of-Line blocking effect. In this paper, we propose an adaptive and HoL-blocking reduction routing algorithm for direct topologies that tries to combine the good properties of both worlds: It provides routing flexibility but also reduces the Head-of-Line blocking effect. To do that, this paper proposes several functions which use the XOR operation to efficiently distribute the packets among virtual channels based on their destination node. The resulting routing mechanisms have different properties depending on whether they enforce routing flexibility or Head-of-Line blocking reduction.

Multipath routing algorithm for application‐specific wormhole NoCs

SummaryAdaptive routing designing for network‐on‐chip architecture is complicated to guarantee deadlock‐free. In this paper, we present methodology to design efficient multi‐path routing algorithms for specific application wormhole network‐on‐chip system to guarantee deadlock‐free. The methodology presents an analytical model for overall average delay of wormhole network‐on‐chip by queueing theory and uses a linear programming–based methodology to minimize overall average delay. The methodology guarantees deadlock freedom by efficient branch‐and‐bound algorithm. Compared to other adaptive deadlock‐free algorithms, results obtained through simulation show that the algorithms can potentially achieve better throughput and latency.

A Highly Scalable Optical Network-on-Chip With Small Network Diameter and Deadlock Freedom

To increase the performance of chip multiprocessors, optical network-on-chip (ONoC) becomes promising because of its high bandwidth and low energy consumption. In this paper, we propose an architecture called RPNoC (Ring-based Packet-switched NoC), which uses few optical devices. Specifically, Single-waveguide RPNoC employs only one waveguide. Multiwaveguide RPNoC introduces space division multiplexing to make the architecture highly scalable. A novel wavelength assignment method and a deadlock-free deterministic routing algorithm are jointly designed, which make the network diameter quite small. This design also guarantees deadlock freedom, a little resource use, and low complexity at the same time. Evaluation is carried out for the 64-node RPNoC under different synthetic and realistic traffic patterns. The simulation result shows that it yields high throughput and low latency. Comparison with other packet-switched ONoCs shows that RPNoC has the lowest energy consumption.

Code aware resource management

Multithreaded programs coordinate their interaction through synchronization primitives like mutexes and semaphores, which are managed by an OS-provided resource manager. We propose algorithms for the automatic construction of code-aware resource managers for multithreaded embedded applications. Such managers use knowledge about the structure and resource usage (mutex and semaphore usage) of the threads to guarantee deadlock freedom and progress while managing resources in an efficient way. Our algorithms compute managers as winning strategies in certain infinite games, and produce a compact code description of these strategies. We have implemented the algorithms in the tool Cynthesis. Given a multithreaded program in C, the tool produces C code implementing a code-aware resource manager. We show in experiments that Cynthesis produces compact resource managers within a few minutes on a set of embedded benchmarks with up to 6 threads.

Tele-operated service robots for household and care

Purpose: Service robots are a relatively new branch of robotics after the successful industry robots and the experimental humanoids. Service robots are supposed to perform tasks that normally are done by humans in particular daily life activities. However they do not have to do it in the same way as humans and neither do they not have to look like a human. Service robots have to operate in environments meant for humans so they have to navigate in environments with unforeseen moving objects and subjects, to mention only one of the challenges. This paper is based on our experience with a tele-operated service robot, named Rose. Tele-operated means that Rose is not completely autonomous but that it is remotely controlled by a human operator. The human operator has the option to control the robot manually or provide indications to carry out complex coordinated procedures (eg. move and grab object). Tele-operated service robots have a wide range of applications, such as in the building industry to carry and place heavy objects, or in the security business. We focused on daily life household tasks. Experiments with Rose were performed in a field lab setting, for the care of elderly people. They need attention several times a day, but in total not more than two hours. This means that one operator can service several homes. This results in a five-fold productivity improvement of care takers. After an introduction on tele-operated service robots, we concisely present the system design of Rose. Then we sketch the field lab experiments and we consider the lessons learned. Based on this information we present some scenarios for the future of tele-operated service robots for caretaking and household tasks. Both the technical and the application aspects will be covered. Method First, a number of general purpose use cases covering daily household activities such as warming a meal, picking and placing objects, turning on the light etc. were defined. From these use cases, the system architecture of Rose was derived using a construction technique called correctness by construction. This construction technique guarantees deadlock freedom and livelock freedom. The software development was carried out using the popular Robot Operating System (ROS) framework. Four rounds of tests covering all use cases were carried out by nurses from a care organization called Zuid Zorg in Waalre, the Netherlands. In the first three sessions the cockpit was located in a room next to the robot. In the fourth session, the cockpit was located in Veldhoven, another nearby town, while the robot remained in Waalre. Results from each test round were used to improve the software of Rose. Results & Discussion: From the results of all test sessions we were able to confirm feasibility in real-life scenarios and increased productivity by an operator while servicing multiple homes. Furthermore, consistency in performance can be achieved by exploiting the robots autonomy. Keywords: Correctness by construction; Home-care; Service robots

A trace-based service semantics guaranteeing deadlock freedom

We revise the accordance preorder in the context of deadlock freedom for asynchronously communicating services. Accordance considers all controllers of a service—that is, all environments that can interact with the service without deadlocking. A service Impl accords with a service Spec if every controller of Spec is also a controller of Impl. We model finite-state and infinite-state services as Petri nets and formalize the semantics of such models with a traditional concurrency semantics, a trace-based semantics. As benefits, we get an easier characterization of the accordance preorder, prove that it is a fully abstract precongruence, and present an algorithm to decide refinement of two finite-state services. Previously, operating guidelines have been introduced to study the behavior of finite-state services; they characterize all controllers of a given service and can be used to decide accordance. An operating guideline is a finite automaton annotated with Boolean formulae that describes the semantics of a service from the perspective of its controllers rather than from the perspective of the service. We show that our trace-based semantics can be translated back and forth into operating guidelines, thereby providing a more conceptual understanding of operating guidelines.

A Type System for Unstructured Locking that Guarantees Deadlock Freedom without Imposing a Lock Ordering

Deadlocks occur in concurrent programs as a consequence of cyclic resource acquisition between threads. In this paper we present a novel type system that guarantees deadlock freedom for a language with references, unstructured locking primitives, and locks which are implicitly associated with references. The proposed type system does not impose a strict lock acquisition order and thus increases programming language expressiveness.

A generic adaptive path-based routing method for MPSoCs

Several unicast routing protocols have been presented for unicast traffic in MPSoCs. Exploiting the unicast routing algorithms for multicast traffic increases the likelihood of deadlock and congestion. In order to avoid deadlock for multicast traffic, the Hamiltonian path strategy was introduced. The traditional Hamiltonian path routing protocols supporting both unicast and multicast traffic are based on deterministic models, leading to lower performance. In this paper, we propose an adaptive routing protocol for both unicast and multicast traffic without using virtual channels. The proposed method maximizes the degree of adaptiveness of the routing functions which are based on the Hamiltonian path while guaranteeing deadlock freedom. Furthermore, both unicast and multicast aspects of the presented method have been widely investigated separately. Results obtained in both synthetic and real traffic models show that the proposed adaptive method for multicast and unicast aspects has lower latency and power dissipation compared to previously proposed path-based multicasting algorithms with negligible hardware overhead.

A methodology for developing deadlock-free dynamic network reconfiguration processes. Part II

For pt.I see ibid., vol.16, no.5, p.412-427 (2005). Dynamic network reconfiguration is defined as the process of changing from one routing function to another while the network remains up and running. The main challenge is in avoiding deadlock anomalies while keeping restrictions on packet injection and forwarding minimal. Current approaches either require virtual channels in the network or they work only for a limited set of routing algorithms and/or fault patterns. In this paper, we present a methodology for devising deadlock free and dynamic transitions between old and new routing functions that is consistent with newly proposed theory [J. Duato et al., (2005)]. The methodology is independent of topology, can be applied to any deadlock-free routing function, and puts no restrictions on the routing function changes that can be supported. Furthermore, it does not require any virtual channels to guarantee deadlock freedom. This research is motivated by current trends toward using increasingly larger Internet and transaction processing servers based on clusters of PCs that have very high availability and dependability requirements, as well as other local, system, and storage area network-based computing systems.

Applying in-transit buffers to boost the performance of networks with source routing

In this paper, we analyze in depth the effect of using ITB in the network, showing that they not only serve for guaranteeing minimal routing, but also that they are a powerful mechanism able to balance network traffic and reduce network contention. To demonstrate these capabilities, we apply the ITB mechanism to improved routing schemes, such as DFS and smart-routing. These routing algorithms (without ITB) are able to improve the performance of up*/down* by 30 percent and 90 percent, respectively, for a 32-switch network. The evaluation results show that, when ITB are used together with these improved routing algorithms, network throughput achieved by DFS and smart-routing can still be improved by 56 percent and 23 percent, respectively. However, smart-routing requires a time to compute the routing tables that rapidly grows with network size, it being impossible in practice to build networks with more than 32 switches. This high computational cost is mainly motivated by the need of obtaining deadlock-free routing tables. However, when ITB are used, one can decouple the stages of computing routing tables and breaking cycles. Moreover, as stated above, ITB can be used to reduce network contention. In this way, in this paper, we also propose a completely new routing algorithm that tries to balance network traffic by using a simple and low time consuming strategy. The proposed algorithm guarantees deadlock freedom and reduces network contention with the use of ITB. The evaluation results show that our algorithm obtains unprecedented throughputs in 32-switch networks, tripling the original up*/down* and almost doubling smart-routing.

Automation of Self-Recovery Resource Allocation Procedures Synthesis in FMS

A fault-tolerant resource allocation procedure aimed at automatic modification of Petri net-based control models is presented. The recovery scheme is based on the assumption that some of the system shared resources may be replaced by others, e.g. in case of their malfunctioning. The method encompasses a new deadlock avoidance algorithm which guarantees deadlock freedom of the control models. Its application for development of controls for computer integrated assembly cells is shown in an example.

A non-two-phase locking protocol for global concurrency control in distributed heterogeneous database systems

A concurrency control method is proposed for global transactions in a distributed heterogeneous database system. This method is applicable when the database sites are interconnected in a rooted tree fashion. It guarantees deadlock freedom in addition to serializability. A general architecture of a heterogeneous system is given. The global transaction manager (GTM) decomposes the global transactions initiated at a site and the subtransactions received from other sites into smaller subtransactions, some of which are sent to the GTMs of the other sites, and those remaining, called g-local transactions, are to be executed by the local transaction manager (LTM) at that site. A concurrency control mechanism ensures serializability among: the local transactions (including the g-local transactions of the global ones) at each site, the global transactions and the global and local transactions together.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A framework for adaptive routing in multicomputer networks

Message-passing concurrent computers, also known as multicomputers, such as the Caltech Cosmic Cube [47] and its commercial descendents, consist of many computing nodes that interact with each other by sending and receiving messages over communication channels between the nodes. The communication networks of the second-generation machines, such as the Symult Series 2010 and the Intel iPSC2 [2], employ an oblivious wormhole-routing technique that guarantees deadlock freedom. The network performance of this highly evolved oblivious technique has reached a limit of being capable of delivering, under random traffic, a stable maximum sustained throughput of ~~45 to 50% of the limit set by the network bisection bandwidth, while maintaining acceptable network latency. This thesis examines the possibility of performing adaptive routing as an approach to further improving upon the performance and reliability of these networks. In an adaptive multipath routing scheme, message trajectories are no longer deterministic, but are continuously perturbed by local message loading. Message packets will tend to follow their shortest-distance routes to destinations in normal traffic loading, but can be detoured to longer but less-loaded routes as local congestion occurs. A simple adaptive cut-through packet-switching framework is described, and a number of fundamental issues concerning the theoretical feasibility of the adaptive approach are studied. Freedom of communication deadlock is achieved by following a coherent channel protocol and by applying voluntary misrouting as needed. Packet deliveries are assured by resolving channel-access conflicts according to a priority assignment. Fairness of network access is assured either by sending round-trip packets or by having each node follow a local injection-synchronization protocol. The performance behavior of the proposed adaptive cut-through framework is studied with stochastic modeling and analysis, as well as through extensive simulation experiments for the 2D and 3D rectilinear networks. Theoretical bounds on various average network-performance metrics are derived for these rectilinear networks. These bounds provide a standard frame of reference for interpreting the performance results. In addition to the potential gain in network performance, the adaptive approach offers the potential for exploiting the inherent path redundancy found in richly connected networks in order to perform fault-tolerant routing. Two convexity-related notions are introduced to characterize the conditions under which our adaptive routing formulation is adequate to provide fault-tolerant routing, with minimal change in routing hardware, The effectiveness of these notions is studied through extensive simulations, The 2D octagonal-mesh network is suggested; this displays excellent fault-tolerant potential under the adaptive routing framework. Both performance and reliability behaviors of the octagonal mesh are studied in detail. A number of