This book provides an in-depth description of event-based systems, covering topics ranging from local event matching and distributed event forwarding algorithms, through a practical discussion of software engineering issues raised by the event-based style, to state-of-the-art research in event-based systems like composite event detection and security. The authors offer a comprehensive overview, and show the power of event-based architectures in modern system design, encouraging professionals to exploit this technique in next generation large-scale distributed applications like information dissemination, network monitoring, enterprise application integration, or mobile systems.

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Distributed event-based systems

In early 2018, Meltdown first showed how to read arbitrary kernel memory from user space by exploiting side-effects from transient instructions. While this attack has been mitigated through stronger isolation boundaries between user and kernel space, Meltdown inspired an entirely new class of fault-driven transient-execution attacks. Particularly, over the past year, Meltdown-type attacks have been extended to not only leak data from the L1 cache but also from various other microarchitectural structures, including the FPU register file and store buffer. In this paper, we present the ZombieLoad attack which uncovers a novel Meltdown-type effect in the processor's fill-buffer logic. Our analysis shows that faulting load instructions (i.e., loads that have to be re-issued) may transiently dereference unauthorized destinations previously brought into the fill buffer by the current or a sibling logical CPU. In contrast to concurrent attacks on the fill buffer, we are the first to report data leakage of recently loaded and stored stale values across logical cores even on Meltdown- and MDS-resistant processors. Hence, despite Intel's claims, we show that the hardware fixes in new CPUs are not sufficient. We demonstrate ZombieLoad's effectiveness in a multitude of practical attack scenarios across CPU privilege rings, OS processes, virtual machines, and SGX enclaves. We discuss both short and long-term mitigation approaches and arrive at the conclusion that disabling hyperthreading is the only possible workaround to prevent at least the most-powerful cross-hyperthread attack scenarios on current processors, as Intel's software fixes are incomplete.

ZombieLoad: Cross-Privilege-Boundary Data Sampling

In early 2018, Meltdown first showed how to read arbitrary kernel memory from user space by exploiting side-effects from transient instructions. While this attack has been mitigated through stronger isolation boundaries between user and kernel space, Meltdown inspired an entirely new class of fault-driven transient execution attacks. Particularly, over the past year, Meltdown-type attacks have been extended to not only leak data from the L1 cache but also from various other microarchitectural structures, including the FPU register file and store buffer. 
In this paper, we present the ZombieLoad attack which uncovers a novel Meltdown-type effect in the processor's previously unexplored fill-buffer logic. Our analysis shows that faulting load instructions (i.e., loads that have to be re-issued for either architectural or microarchitectural reasons) may transiently dereference unauthorized destinations previously brought into the fill buffer by the current or a sibling logical CPU. Hence, we report data leakage of recently loaded stale values across logical cores. We demonstrate ZombieLoad's effectiveness in a multitude of practical attack scenarios across CPU privilege rings, OS processes, virtual machines, and SGX enclaves. We discuss both short and long-term mitigation approaches and arrive at the conclusion that disabling hyperthreading is the only possible workaround to prevent this extremely powerful attack on current processors.

Due to stringent constraints in memory footprint, processing efficiency and power consumption, traditional wireless sensor networks (WSNs) face two key issues: (1) a lack of interoperability with access networks and (2) a lack of flexibility to customize non-functional properties such as event filtering, data aggregation and routing. In order to address these issues, this chapter investigates interoperable publish/subscribe middleware for WSNs. The proposed middleware, called TinyDDS, enables the interoperability between WSNs and access networks by providing programming language interoperability and protocol interoperability based on the standard Data Distribution Service (DDS) specification. Moreover, TinyDDS provides a pluggable framework that allows WSN applications to have fine-grained control over application-level and middleware-level non-functional properties. Simulation and empirical evaluation results demonstrate that TinyDDS is lightweight and efficient on the TinyOS and SunSPOT platforms. The results also show that TinyDDS simplifies the development of publish/subscribe WSN applications.

TinyDDS: An Interoperable and Configurable Publish/Subscribe Middleware for Wireless Sensor Networks

Comparison of scheduling schemes for on-demand IaaS requests

In this paper, we present a new method to realize a selforganizing and self-stabilizing publish/subscribe middleware for wireless actuator and sensor networks. By using simple, yet powerful compositional rules, our approach forms hierarchical clusters of nodes and sets up many small publish/subscribe networks, that interact with each other. Thereby, we are able to integrate the necessary routing of messages between clusters into the publish/subscribe substrate itself. This technique reveals several benefits, such as redundant routes and automatic route recovery, which show up as emergent behavior at no additional cost. The provided publish/subscribe middleware allows an elegant design of eventbased applications for pervasive environments.

Clustered publish/subscribe in wireless actuator and sensor networks

Energy-efficient computing as a research area has been receiving increasing attention in recent years due to rising energy costs and environmental awareness In this paper, we present an approach to increasing the energy efficiency of modern multi-core computers, which is suitable for scenarios with varying load characteristics often found in private and small office/home office (SOHO) machines The approach is based on a closer integration of the operating system scheduler and frequency governor, while shifting the mode of operation from time-driven to event-driven We discuss theoretical as well as practical considerations, and describe experiments for both desktop and server systems Based on a fully functional implementation within the Linux kernel, it is shown that our approach is feasible and allows for power savings of up to 10% while delivering a performance comparable to disabled power management and being more energy-efficient than the traditional time-driven variant

Event-driven processor power management

Coscheduling, invented originally on early parallel computer systems 30 years ago, provided the possibility to improve the resource utilization of these systems substantially by coordinating the execution of processes across multiple processors in time. Almost forgotten in the multicore era, recent research addressing certain problems on multicore systems, such as performance of virtual machines, contention of processor resources, or dynamic energy budget distribution, concludes that coscheduling is a viable solution.

In this paper, we do not focus on a specific problem or application of coscheduling, but on coscheduling itself. We present a coscheduling design that is able to cover most of the identified use cases on multicore systems and can be seamlessly integrated into currently used general purpose operating systems. We have applied this design to the Linux kernel and show that this approach allows a non-intrusive solution that fulfills the promises of coscheduling and is able to achieve a similar performance as a specialized commercial solution.

Non-intrusive coscheduling for general purpose operating systems

A Scheduling Approach for Efficient Utilization of Hardware-Driven Frequency Scaling.

While OpenMP conceptually allows to vary the degree of parallelism from one parallel region to the next in order to adapt to the system load, this might still be too coarse-grained in certain scenarios. Especially applications designed for parallelism may stay within one parallel region for a long time. This may lead either to an oversubscribed system where individual applications are not restricted in their degree of parallelism, or to an underutilized system, because individual applications are restricted to a too small degree of parallelism. In this paper, we tackle both problems by dynamically restricting the number of active threads within a parallel region without violating the OpenMP specification.

Jan Hendrik Schönherr

Papers

Clustered publish/subscribe in wireless actuator and sensor networks

Event-driven processor power management

Non-intrusive coscheduling for general purpose operating systems

A Scheduling Approach for Efficient Utilization of Hardware-Driven Frequency Scaling.

Dynamic Teams in OpenMP