Architecture of Computing Systems (Lecture Notes in Computer ...

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88 J.-P. Steghöfer et al. � � � Fig. 1. A situation prone to deadlocks induced by cyclic resource processing starvation without the need to globally analyse the system or trace the state of all agents during runtime. The paper is structured as follows: Sect. 2 defines the terms associated with deadlocks and introduces how deadlocks can be dealt with. Sect. 3 shows how liveness hazards are dealt with in literature and Sect. 4 describes the system class the proposed approach is applicable to. Sect. 5 then introduces a fair roleselection algorithm that is extended with a deadlock avoidance mechanism in Sect. 6. Limitations of this mechanism and ways to overcome them are outlined in Sect. 7 and Sect. 8 concludes the paper. 2 Background and Definitions There are a number of different liveness hazards that can occur in concurrent systems. The definitions of these hazards often vary a great deal between different authors and domains. Therefore, the following brief definitions introduce the terms as they are used in this paper. Deadlocks. A deadlock is a situation wherein two or more competing actions are waiting for the other to finish, and thus neither ever does. Coffman et al. [10] give four conditions that must hold for a deadlock to occur: 1. “Mutual exclusion” i.e., agents claim exclusive control of the resource they require; 2. “No preemption” i.e., resources cannot be forcibly removed from the agents holding them until processing of the resources is completed; 3. “Wait for condition” i.e., Agents hold resources allocated to them, while waiting for additional ones; 4. “Circular wait” i.e., a circular claim of agents exists, such that each agent holds one or more resources that need to be given to another agent in the claim. Livelock. A liveness failure is referred to as a livelock when an agent although not blocked cannot proceed further and keeps retrying. As an example consider two mobile agent’s who obstruct each others paths. Both decide to give way to the other at the same time and move to the right leading again to an obstruction. Now both decide at the same time to move to the left and the process keeps repeating leading to no agent moving forward. Another example is the ’after you after you’ politeness protocol. � �
On Deadlocks and Fairness in Self-organizing Resource-Flow Systems 89 Starvation. Starvation occurs when an agent is continuously denied access to a resource. Bustard et al. illustrate the starvation problem using the dining philosophers problem in the field of autonomic computing [8]. It can also be characterized as a special case of livelock [21]. Fairness. Fairness in its most general definition guarantees that a process will eventually be given enough resources to allow it to terminate [26]. This is usually achieved by implementing a scheduling mechanism. Especially in distributed systems that share resources, the ability to terminate may depend on other components or on interacting with them. Fairness is classified into weak and strong fairness where weak fairness implies that a component will eventually proceed if it can almost always proceed and strong fairness implies that a component which can proceed infinitely often does proceed infinitely often [11]. There are three different ways on how potential deadlocks can be dealt with. Their applicability depends on the structure of the systems under consideration and the assumptions that can be made about them. Deadlock Prevention prohibits circular waits among agents while the system is not running. The strength of the approach is also its greatest weakness: a prevention mechanism requires global knowledge of the system and all its reachable states which often yields a straightforward often-simple control law but acquiring this knowledge can be difficult and computationally intractable. Additionally, limiting concurrency to prevent any deadlock state from occurring can be overly conservative, potentially leading to low utilization of system resources. Deadlock Avoidance suitable governs the resource flow to prevent circular waits. This is a dynamic approach that can utilize the knowledge of the current allocation of resources and the future behaviour of processes to control the release and acquisition of resources. The main characteristic of deadlock avoidance strategies is that they work during runtime and base their decisions on information about the resource and agent status. More precisely, a deadlock controller inhibits or enables events involving resource acquisition or release by using look-ahead procedures. Deadlock Detection and Resolution monitors the agents and/or the flow of resources and detects deadlocks at runtime. Resources can then be removed from the system or put into buffers to resolve the deadlock. This strategy can in general allow higher resource utilization than that prevention or avoidance methods can offer. However, it should only be used when deadlock is rare and detection and recovery are not expensive and much faster than deadlock generation. 3 Related Work Deadlocks have been dealt with in several domains that are concerned with software-systems, e.g. deadlocks which are inherent in databases that use locking
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Lecture Notes in Computer Science 5
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Volume Editors Christian Müller-Sc
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General Chair Organization Christia
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Organization IX Hartmut Schmeck Kar
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Keynote Table of Contents HyVM - Hy
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Table of Contents XIII JetBench:AnO
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How to Enhance a Superscalar Proces
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4 J. Mische et al. The Real-time Vi
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6 J. Mische et al. 4.1 Instruction
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8 J. Mische et al. Additionally the
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10 J. Mische et al. % of unused pip
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12 J. Mische et al. % of cycles spe
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14 J. Mische et al. 16. Lickly, B.,
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16 G. Aşılıoğlu, E.M. Kaya, and
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26 T.B. Preußer, P. Reichel, and R
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Efficient Transaction Nesting in Ha
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140 Y. Liu et al. HTMs include TCC
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142 Y. Liu et al. rollback T0 begin
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144 Y. Liu et al. Processor core Pr
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146 Y. Liu et al. 5.2 Results and A
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148 Y. Liu et al. decreases, partia
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Decentralized Energy-Management to
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152 B. Becker et al. Furthermore, t
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154 B. Becker et al. An optimizing
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156 B. Becker et al. smart-home man
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158 B. Becker et al. freedom like w
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160 B. Becker et al. Power [W] 4500
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EnergySaving Cluster Roll: Power Sa
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164 M.F. Dolz et al. Themodulequeri
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166 M.F. Dolz et al. This daemon al
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168 M.F. Dolz et al. been submitted
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170 M.F. Dolz et al. On the other h
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172 M.F. Dolz et al. at the inactiv
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Effect of the Degree of Neighborhoo
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176 T. Abdullah et al. A zone based
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178 T. Abdullah et al. A consumer/p
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180 T. Abdullah et al. Messages 140
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184 T. Abdullah et al. % Matchmakin
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186 T. Abdullah et al. show that th
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224 F. Nowak and R. Buchty where A
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226 F. Nowak and R. Buchty Fig. 3.
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228 F. Nowak and R. Buchty Table 2.
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230 F. Nowak and R. Buchty Table 4.
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232 F. Nowak and R. Buchty 5.3 Comp
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Optimizing Stencil Application on M
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236 F. Xudong et al. compared to th
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238 F. Xudong et al. stencil comput
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240 F. Xudong et al. threads in the
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242 F. Xudong et al. Speedup 14 12
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244 F. Xudong et al. 5 Related Work
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Abdullah, Tariq 174 Alima, Luc Onan
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