Online update is a technique that reduces the disruption caused by a software update. It does so by applying a patch to a running process as opposed to shutting down the process and restarting it. The challenge here lies in ensuring correct operation during and after the update. In this paper, we present the correctness criteria involved in such situations and a solution to performing updates safely based on these correctness criteria. The approach we use avoids deadlocks during update by analyzing interthread dependencies and guarantees that the process remains in a consistent state after the update. Thus, the update procedure is guaranteed to terminate and the requests that execute during and after an update are ensured correct execution. Our literature survey reveals that this is amongst the first solutions to update concurrent programs while requests are executing and ensure correctness.
An application's performance can suffer from significant computational overheads when it is moved from a native to a virtualized environment. Adoption of virtualization without understanding such overheads in detail can dramatically impact the overall performance of hosted applications. The rapid adoption of virtualization has fueled the development of new hardware technologies, which promise to optimize the performance and scalability of processor and network I/O virtualization. However, no comprehensive empirical study of the effectiveness of these hardware assistance technologies is publicly available. In this paper we focus on x86 architectures and study empirically the performance improvements introduced by Intel's VT and PCI-SIG's SR-IOV on a Xen-based hypervisor. Using a range of benchmark programs, we compare benchmark scores and resource utilization between native and virtual environments for two different testbeds, one with hardware assistance and one without. The results indicate that hardware assistance indeed eliminates most overheads, especially those relating to network I/O, but non-negligible CPU overheads still remain. Also, there is no hardware technology with specifically deals with disk I/O virtualization, and significant overheads do arise in workloads requiring intensive disk usage.
Filtering is an emerging abstraction in object‐oriented systems. Filtering can be characterized by an ability to filter messages in transit and perform intermediate actions. Filters can be used for carrying out intermediate tasks such as encryption, load balancing, caching, security checks and add‐on computations. A few filtering approaches have been proposed earlier and some commercial implementations with specialized filtering capabilities are available. This paper discusses a model for transparent and dynamically pluggable first class filter objects for object‐oriented systems based on the Java programming language. The filter object model is based on an interclass filter relationship. The model is realized through extensions to the Java programming language. Filter objects can be injected into message paths during execution time and they are transparent to both clients and servers. The properties of filter objects enable them to be employed as a mechanism for evolution promoting reuse of existing code. A method of evolution through filter objects is discussed. A translator for Java filters (TJF) has been designed and implemented. TJF translates an extended Java program involving filter constructs into an equivalent Java code. The translation scheme is presented and the performance of the translated code is analyzed. A brief survey of existing approaches related to filtering in object‐oriented systems has also been presented. Copyright © 2003 John Wiley & Sons, Ltd.
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