Complexity reduction in enforcing disjunctive generalized mutual exclusion constraints

Design of control laws for timed event graphs networks subject to mutual exclusion constraints in Min-Plus algebra

We consider the problem of scheduling dependent real-time tasks for overloads on a multiprocessor system, yielding best-effort timing assurance. The application/scheduling model includes tasks with time/utility function time constraints, mutual exclusion constraints, and arbitrary arrival, execution-time and resource access behaviors, with timeliness optimization objective of maximizing total accrued utility while ensuring mutual exclusion constraints and deadlock-freedom. Since this problem is NP-hard, we develop a class of polynomial-time heuristic algorithms, called the Global Utility Accrual (GUA), and present two algorithm instances, namely, Non-Greedy Global Utility Accrual (NG-GUA) and Greedy Global Utility Accrual (G-GUA). We establish several properties of the algorithms including conditions under which optimal total utility is accrued, mutual exclusion constraints are satisfied, and deadlock-freedom is achieved. We develop a Linux-based real-time kernel called ChronOS, extended from PREEMPT_RT real-time patch. ChronOS provides a framework for implementation of a variety of multiprocessor schedulers. Our experimental studies with ChronOS reveal the effectiveness of GUA algorithms under a broad range of workloads.Keywordsreal-timemultiprocessorsschedulingtime/utility functions

We present a utility accrual real-time scheduling algorithm called CIC-VCUA for tasks whose execution times are functions of their starting times (and, potentially, other factors). We model such variable execution times using variable cost functions (or VCFs). The algorithm considers application activities that are subject to time/utility function time constraints, execution times described using VCFs, and mutual exclusion constraints on concurrent sharing of non-CPU resources. We consider the twofold scheduling objective of 1) assuring that the maximum interval between any two consecutive, successful completions of job instances in an activity must not exceed the activity period (an application-specific objective) and 2) maximizing the system's total accrued utility while satisfying mutual exclusion resource constraints. Since the scheduling problem is intractable, CIC-VCUA is a polynomial-time heuristic algorithm. The algorithm statically computes worst-case task sojourn times, dynamically selects tasks for execution based on their potential utility density, and completes tasks at specific times. We establish that CIC-VCUA achieves optimal timeliness during underloads, and tightly upper bounds inter and intratask completion times. Our simulation experiments confirm the algorithm's effectiveness and superiority

Consider the problem of scheduling sporadic tasks on a multiprocessor platform under mutual exclusion constraints. We present an approach which appears promising for allowing large amounts of parallel task executions and still ensures low amounts of blocking.

The multi-trip vehicle routing problem with time windows and unloading queue at depot

Voting is used commonly to enforce mutual exclusion in distributed systems. Each node is assigned a number of votes, and only the group with a majority of votes is allowed to perform a restricted operation. This paper describes techniques for dynamically reassigning votes upon node or link failure, in an attempt to make the system more resilient to future failures. We focus on autonomous methods for achieving this, that is, methods that allow the nodes to make independent choices about changing their votes and picking new vote values, rather than group consensus techniques that require tight coordination among the remaining nodes. Protocols are given which allow nodes to install new vote values while still maintaining mutual exclusion requirements. The lemmas and theorems to validate the protocols are presented. A simple example shows how to apply the method to a database object-locking scheme; the protocols, however, are versatile andgeneral purpose, and can be used foranyapplication requiring mutual exclusion. In addition, policies are presented that allow nodes to autonomously select their new vote values. Simulation results are presented comparing the autonomous methods to static vote assignments and to group consensus strategies. These results demonstrate that under high failure rates, dynamic vote reassignment shows great improvement over a static assignment of votes in terms of availability. In addition, many autonomous methods for determining a new vote assignment yield almost as much availability as a group consensus method and at the same time are faster and more flexible.

In a business process context, access permissions grant the rights to perform certain tasks. In particular, process-related role-based access control (RBAC) models define RBAC policies for process-aware information systems (PAIS). In addition, process-related RBAC models allow for the definition of entailment constraints on tasks, such as mutual exclusion or binding constraints, for example. This paper presents an approach to derive process-related RBAC models from process execution histories recorded by a PAIS. In particular, we present algorithms to derive corresponding RBAC artifacts and entailment constraints from standardized XML-based log files. All algorithms presented in this paper have been implemented and were tested via process logs created with CPN Tools.

ContextA distributed business process is executed in a distributed computing environment. The service-oriented architecture (SOA) paradigm is a popular option for the integration of software services and execution of distributed business processes. Entailment constraints, such as mutual exclusion and binding constraints, are important means to control process execution. Mutually exclusive tasks result from the division of powerful rights and responsibilities to prevent fraud and abuse. In contrast, binding constraints define that a subject who performed one task must also perform the corresponding bound task(s). ObjectiveWe aim to provide a model-driven approach for the specification and enforcement of task-based entailment constraints in distributed service-based business processes. MethodBased on a generic metamodel, we define a domain-specific language (DSL) that maps the different modeling-level artifacts to the implementation-level. The DSL integrates elements from role-based access control (RBAC) with the tasks that are performed in a business process. Process definitions are annotated using the DSL, and our software platform uses automated model transformations to produce executable WS-BPEL specifications which enforce the entailment constraints. We evaluate the impact of constraint enforcement on runtime performance for five selected service-based processes from existing literature. ResultsOur evaluation demonstrates that the approach correctly enforces task-based entailment constraints at runtime. The performance experiments illustrate that the runtime enforcement operates with an overhead that scales well up to the order of several ten thousand logged invocations. Using our DSL annotations, the user-defined process definition remains declarative and clean of security enforcement code. ConclusionOur approach decouples the concerns of (non-technical) domain experts from technical details of entailment constraint enforcement. The developed framework integrates seamlessly with WS-BPEL and the Web services technology stack. Our prototype implementation shows the feasibility of the approach, and the evaluation points to future work and further performance optimizations.

A distributed business process is executed in a distributed computing environment. In this context, the service-oriented architecture (SOA) paradigm provides a mature and well-understood framework for the integration of software services. Entailment constraints, such as mutual exclusion or binding constraints, are an important means to specify and enforce business processes in a SOA. Process engines control the process flow and are responsible for the coordination of the services that participate in a distributed business process. Since the enforcement of entailment constraints requires knowledge of the subjects and roles who executed particular task instances, we need to communicate the execution history of the respective tasks and processes between the services and the process engines. However, the inherent concurrency of a distributed system may lead to omission failures. Such failures may impair the enforcement of entailment constraints in a process-driven SOA. In particular, the impact of these failures as well as the corresponding countermeasures depend on the architecture of the respective process engine. In this paper, we discuss communication schemes for (distributed) process execution histories in a SOA. In particular, we provide generic procedures for different communication schemes and examine the efficiency of these schemes as well as their characteristics if omission failures occur. In this context, we especially consider if the respective process engine acts as an orchestration engine or as a choreography engine.

A distributed business process is executed in a distributed computing environment. In this context, the service-oriented architecture (SOA) paradigm provides a mature and well understood framework for the integration of software services. Entailment constraints, such as mutual exclusion or binding constraints, are an important means to specify and enforce business processes in a SOA. However, the inherent concurrency of a distributed system may lead to omission and ordering failures. Such failures impact the enforcement of entailment constraints in a process-driven SOA. In particular, the impact of these failures as well as the corresponding countermeasures depend on the architecture of the respective process engine. In this paper, we discuss the impact of omission and ordering failures on the enforcement of entailment constraints in process-driven SOAs. In this context, we especially consider if the respective process engine acts as an orchestration engine or as a choreography engine.

Connector colouring I: Synchronisation and context dependency

This paper deals with the study of the reconfiguration of embedded control systems with safety following component-based approaches from the functional level to the operational level. The authors define the architecture of the Reconfiguration Agent which is modelled by nested state machines to apply local reconfigurations. They propose in this journal paper technical solutions to implement the whole agent-based architecture, by defining UML meta-models for both Control Components and also agents. To guarantee safety reconfigurations of tasks at run-time, they define service and reconfiguration processes for tasks and use the semaphore concept to ensure safety mutual exclusions. As a method to ensure the scheduling between periodic tasks with precedence and mutual exclusion constraints, the authors apply the priority ceiling protocol.

The chapter deals with run-time automatic reconfigurations of distributed embedded control systems following component-based approaches. We classify reconfiguration scenarios into four forms: (1) additions-removals of components, (2) modifications of their compositions, (3) modifications of implementations, and finally (4) simple modifications of data. We define a new multi-agent architecture for reconfigurable systems where a Reconfiguration Agent which is modelled by nested state machines is affected to each device of the execution environment to apply local reconfigurations, and a Coordination Agent is proposed for any coordination between devices in order to guarantee safe and coherent distributed reconfigurations. We propose technical solutions to implement the whole agent-based architecture, by defining UML meta-models for agents. In the execution scheme, a task is assumed to be a set of components having some properties independently from any real-time operating system. To guarantee safety reconfigurations of tasks at run-time, we define service and reconfiguration processes for tasks and use the semaphore concept to ensure safety mutual exclusions. We apply the priority ceiling protocol as a method to ensure the scheduling between periodic tasks with precedence and mutual exclusion constraints.

This paper deals with the study of Embedded Control System through Real-Time Task. In the embedded control system, we decompose a component into several real-time tasks. To ensure safety control of tasks at run-time, we define service and reconfiguration processes for tasks and use the semaphore concept to obtain safety mutual exclusions. The Priority Ceiling Protocol (PCP) is applied as an approach to ensure the scheduling between periodic tasks with precedence and mutual exclusion constraints. We simulate the scheduling of Real-time tasks with PCP through the Cheddar tool.

The authors study the safety reconfiguration of embedded control systems following component-based approaches from the functional level to the operational level. At the functional level, a Control Component is defined as an event-triggered software unit characterized by an interface that supports interactions with the environment (the plant or other Control Components). They define the architecture of the Reconfiguration Agent, which is modelled by nested state machines to apply local reconfigurations. The authors propose technical solutions to implement the agent-based architecture by defining UML meta-models for both Control Components and also agents. At the operational level, a task is assumed to be a set of components having some properties independently from any real-time operating system. To guarantee safety reconfigurations of tasks at run-time, the authors define service and reconfiguration processes for tasks and use the semaphore concept to ensure safety mutual exclusions. They apply the priority ceiling protocol as a method to ensure the scheduling between periodic tasks with precedence and mutual exclusion constraints.