No abstract

Dynamically updating language runtime and core libraries such as collections and threading is challenging since the update mechanism uses such libraries at the same time that it modifies them. To tackle this challenge, we present Dynamic Core Library Update (DCU) as an extension of Dynamic Software Update (DSU) and our approach based on a virtualization architecture. Our solution supports the update of core libraries as any other normal library, avoiding the circular dependencies between the updater and the core libraries. Our benchmarks show that there is no evident performance overhead in comparison with a default execution. Finally, we show that our approach can be applied to real life scenario by introducing a critical update inside a web application with 20 simulated concurrent users.

Dynamic Software Update (DSU) solutions update applications while they are executing. These solutions are typically used in production to minimize application downtime, or in integrated development environments to provide live programming support. Each of these scenarios presents different challenges, forcing existing solutions to be designed with only one of these use cases in mind. For example, DSUs for live programming typically do not implement safe point detection or instance migration, while production DSUs require manual generation of patches and lack IDE integration. Also, these solutions have limited ability to update themselves or the language core libraries, and some of them present execution penalties outside the update window. We propose a DSU (gDSU) that works for both live programming and production environments. Our solution implements safe update point detection using call stack manipulation and a reusable instance migration mechanism to minimize manual intervention in patch generation. Moreover, it also offers updates of core language libraries and the update mechanism itself. This is achieved by the incremental copy of the modified objects and an atomic commit operation. We show that our solution does not affect the global performance of the application and it presents only a run-time penalty during the update window. Our solution is able to apply an update impacting 100,000 instances in 1 second. In this 1 second, only during 250 milliseconds the application is not responsive. The rest of the time the application runs normally while gDSU is looking for the safe update point. The update only requires to copy the elements that are modified.

Context Recent studies show that developers spend most of their programming time testing, verifying and debugging software. As applications become more and more complex, developers demand more advanced debugging support to ease the software development process.Inquiry Since the 70's many debugging solutions have been introduced. Amongst them, online debuggers provide good insight on the conditions that led to a bug, allowing inspection and interaction with the variables of the program. However, most of the online debugging solutions introduce debugging interference to the execution of the program, i.e. pauses, latency, and evaluation of code containing side-effects.Approach This paper investigates a novel debugging technique called out-of-place debugging. The goal is to minimize the debugging interference characteristic of online debugging while allowing online remote capabilities. An out-of-place debugger transfers the program execution and application state from the debugged application to the debugger application, each running in a different process.Knowledge On the one hand, out-of-place debugging allows developers to debug applications remotely, overcoming the need of physical access to the machine where the debugged application is running. On the other hand, debugging happens locally on the remote machine avoiding latency. That makes it suitable to be deployed on a distributed system and handle the debugging of several processes running in parallel.Grounding We implemented a concrete out-of-place debugger for the Pharo Smalltalk programming language. We show that our approach is practical by running several benchmarks, comparing our approach with a classic remote online debugger. We show that our prototype debugger outperforms a traditional remote debugger by 1000 times in several scenarios. Moreover, we show that the presence of our debugger does not impact the overall performance of an application.Importance This work combines remote debugging with the debugging experience of a local online debugger. Out-of-place debugging is the first online debugging technique that can minimize debugging interference while debugging a remote application. Yet, it still keeps the benefits of online debugging (e.g., step-by-step execution). This makes the technique suitable for modern applications which are increasingly parallel, distributed and reactive to streams of data from various sources like sensors, UI, network, etc. ACM CCS 2012Software and its engineering → Software testing and debugging;