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A large amount of research has shown the vitality of siphon enumeration in the analysis and control of deadlocks in various resource-allocation systems modeled by Petri nets (PNs). In this paper, we propose an algorithm for the enumeration of minimal siphons in PN based on problem decomposition. The proposed algorithm is an improved version of the global partitioning minimal-siphon enumeration (GPMSE) proposed by Cordone et al. (2005) in IEEE Transactions on Systems, Man, and Cybernetics-Part A: Systems and Humans, which is widely used in the literature to compute minimal siphons. The experimental results show that the proposed algorithm consumes lower computational time and memory compared with GPMSE, which becomes more evident when the size of the handled net grows.

Deadlock is an undesired situation in multithreaded software since it can lead to the stoppage of software. This paper studies the problem of deadlock control of multithreaded software based on Gadara nets, which are well studied for modelling concurrent programs. In particular, an iterative deadlock prevention policy based on siphons is proposed for a class of ordinary Gadara nets where the initial marking of each idle place is one. At each iteration, we compute emptiable siphons containing the smallest number of resource places. Then, bad markings are computed based on these siphons. On the basis of the bad markings, a constraint is constructed that forbids not only bad markings that empty one of the siphons but also some other bad markings. The algorithm is carried out until no emptiable siphon exists in the net. Compared with the existing methods, the resultant net derived from the proposed method is live and maximally permissive with a simpler supervisor. Finally, two examples are provided to illustrate the proposed deadlock prevention policy.

In recent years, opacity has received increasing attention in terms of analyzing security and privacy problems. Opacity is a confidentiality property that characterizes a system’s ability to hide its secret information from any external intruders. A systematic overview of opacity in the context of discrete event systems (DESs) was conducted; this paper firstly reviews the verification methods and computational complexity of the opacity in DESs using the formalisms of automata and Petri nets. When the system is verified to be non-opaque, the approaches that synthesize an opaque system are summarized. Finally, the future research directions and open problems of opacity in DES are also reviewed.

This paper focuses on establishing a Petri net (PN)-based deadlock prevention policy for large-scale systems whose state spaces are prone to the explosion problem phenomenon. When using the reachability analysis technique, the main burden is that the number of states grows exponentially with respect to the PN structure and, thereby, synthesizing a lively controlled Petri net model (PNM) becomes an extremely complex procedure. The proposed method reduces the initial marking of the PNM to reduce the size of the reachability graph. Such a reachability graph is reduced exponentially and the activity places are derived iteratively using a well-established invariant-based control method. When the PNM becomes live, the control places are integrated to the original PNM and, therefore, the advantage of this method lies in that the control of the original PN model starts at an earlier stage, i.e., before enumerating the full reachability graph and which we call it one-step control-ahead of a PNM. Compared with the existing methods, the new method requires the control of a very small-sized reachability graph and, therefore, it is convenient for large-scale and bounded PNs. Two examples are used to illustrate the proposed approach. Experimental results show that we can obtain optimal supervisors for the net models.

Safety issue of vehicular platoons remains a critical challenge and is still open for investigation. In this study, the authors propose an accurate simulation model for vehicular platoons, taking into consideration of the kinematics and dynamics aspects of the platoon and its physical constraints. A hybrid controller formed by two different longitudinal and lateral proportional-integral-derivative controllers and two operation modes at the same time is developed and simulated using Webots. By this study, the aim is to deeply study the performance of the platoon and reveal its weakness in real scenarios. The latter includes normal/degraded operating modes, different speeds, full brake scenarios and various global positioning system accuracies. Results show the efficiency of the platoon controller even in the predefined degraded mode.

In order to cope with uncertainties in a platoon, this paper proposes a reconfigurable multi-agent architecture to address the platoon safety problem by handling two modes: the normal mode and the degraded mode. At this stage of research, the normal mode is characterized by the interaction between agents over a Vehicle-to-Vehicle (V2V) communication network while the degraded mode simply involves sensors for a local perception. The switching from the normal mode to the degraded one is triggered when the communication quality is considered not fully reliable. A PID (Proportional Integral Derivative) controller is proposed to regulate the inter-vehicle distance and orientation. Two models are proposed in this paper: in the first one, the management operations such as splitting and joining are set up while the second is mainly modeled to assess the implemented controller quality. In this paper, the safety of a platoon is represented by the quality of tracking and the inter-vehicle distance. The mentioned features are assessed for both modes through a formal verification using the Uppaal software. We prove the efficiency of the proposed platoon model for several situations such as merging, following or leaving the platoon by verifying different properties using the model checking. The evaluation of the second model, simulated by the Webots software, proves the impact of the number of vehicles on the platoon performance and the vehicle tracking quality. We conclude that when the platoon reaches a certain number of vehicles, the safety criterion is no more reliable.