Abstract-We introduce WaRR, a tool that records and replays with high fidelity the interaction between users and modern web applications. WaRR consists of two independent components: the WaRR Recorder and the WaRR Replayer.The WaRR Recorder is embedded in a web browser, thus having access to user actions, and provides a complete interaction trace-this confers high recording fidelity. The WaRR Replayer uses an enhanced, developer-specific web browser that enables realistic simulation of user interaction-this confers high replaying fidelity.We describe two usage scenarios for WaRR that help developers improve the dependability of web applications: testing web applications against realistic human errors and generating user experience reports. WaRR helped us discover bugs in widely-used web applications, such as Google Sites, and offers higher recording fidelity compared to current tools.

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Abstract. Deadlock immunity is a property by which programs, once afflicted by a deadlock, develop resistance against future occurrences of that deadlock. Our deadlock immunity system, called Dimmunix, provides transparent immunization against deadlocks involving mutex locks. In this paper, we focus on efficiently protecting systems against deadlocks regardless of the rate of synchronization operations performed. We describe five optimizations that reduce the runtime overhead imposed by Dimmunix on the host system: (1) offline deadlock detection and signature extraction, which avoids runtime tracking of lock-to-thread allocations; (2) selective program instrumentation, whereby only vulnerable synchronization statements are monitored; (3) inline matching of deadlock signatures, which avoids expensive call stack retrieval; (4) false positive reduction, which avoids unnecessary thread serialization; and (5) safe early resumption of threads, allowing suspended threads to resume their execution more quickly than in the original Dimmunix. Our optimizations enable Dimmunix to achieve a reduction of 2.8x-5.2x in the runtime overhead it introduces for real-world systems like Eclipse, Vuze, and MySQL JDBC.