UWSpace

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Recent Submissions

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    A Template for Implementing Fast Lock-free Trees Using HTM
    (Association for Computing Machinery, 2017-07-25) Brown, Trevor
    Algorithms that use hardware transactional memory (HTM) must provide a software-only fallback path to guarantee progress. The design of the fallback path can have a profound impact on performance. If the fallback path is allowed to run concurrently with hardware transactions, then hardware transactions must be instrumented, adding significant overhead. Otherwise, hardware transactions must wait for any processes on the fallback path, causing concurrency bottlenecks, or move to the fallback path. We introduce an approach that combines the best of both worlds. The key idea is to use three execution paths: an HTM fast path, an HTM middle path, and a software fallback path, such that the middle path can run concurrently with each of the other two. The fast path and fallback path do not run concurrently, so the fast path incurs no instrumentation overhead. Furthermore, fast path transactions can move to the middle path instead of waiting or moving to the software path. We demonstrate our approach by producing an accelerated version of the tree update template of Brown et al., which can be used to implement fast lock-free data structures based on down-trees. We used the accelerated template to implement two lock-free trees: a binary search tree (BST), and an (a,b)-tree (a generalization of a B-tree). Experiments show that, with 72 concurrent processes, our accelerated (a,b)-tree performs between 4.0x and 4.2x as many operations per second as an implementation obtained using the original tree update template.
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    Harnessing Epoch-based Reclamation for Efficient Range Queries
    (Association for Computing Machinery, 2018-02-10) Arbel-Raviv, Maya; Brown, Trevor
    Concurrent sets with range query operations are highly desirable in applications such as in-memory databases. However, few set implementations offer range queries. Known techniques for augmenting data structures with range queries (or operations that can be used to build range queries) have numerous problems that limit their usefulness. For example, they impose high overhead or rely heavily on garbage collection. In this work, we show how to augment data structures with highly efficient range queries, without relying on garbage collection. We identify a property of epoch-based memory reclamation algorithms that makes them ideal for implementing range queries, and produce three algorithms, which use locks, transactional memory and lock-free techniques, respectively. Our algorithms are applicable to more data structures than previous work, and are shown to be highly efficient on a large scale Intel system.
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    Snapshot-Based Synchronization: A Fast Replacement for Hand-over-Hand Locking
    (Springer International Publishing, 2018-08-01) Gilad, Eran; Brown, Trevor; Oskin, Mark; Etsion, Yoav
    Concurrent accesses to shared data structures must be synchronized to avoid data races. Coarse-grained synchronization, which locks the entire data structure, is easy to implement but does not scale. Fine-grained synchronization can scale well, but can be hard to reason about. Hand-over-hand locking, in which operations are pipelined as they traverse the data structure, combines fine-grained synchronization with ease of use. However, the traditional implementation suffers from inherent overheads. This paper introduces snapshot-based synchronization (SBS), a novel hand-over-hand locking mechanism. SBS decouples the synchronization state from the data, significantly improving cache utilization. Further, it relies on guarantees provided by pipelining to minimize synchronization that requires cross-thread communication. Snapshot-based synchronization thus scales much better than traditional hand-over-hand locking, while maintaining the same ease of use.
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    Cross-O-DU Detection of RRC Signaling Storms in 5G O-RAN Networks
    (University of Waterloo, 2026-10-21) Saqib, Eimaan
    Open Radio Access Network (O-RAN) adopts a disaggregated Radio Access Network (RAN) architecture in which O-RAN Centralized Units (O-CUs) and Distributed Units (O-DUs) expose telemetry to operator applications. I use this architecture to detect signaling storms: deliberate or accidental surges of connection-establishment signaling that can degrade service before devices authenticate. Detection is difficult for two reasons. First, a distributed storm can produce moderately elevated evidence at several O-DUs without crossing a per-O-DU alarm threshold. Second, some random-access attempts fail inside the O-DU before their RRC request reaches the O-CU, so O-CU RRC counters alone omit part of the load. I present a tiered, unsupervised detector: one Isolation Forest per O-DU produces calibrated anomaly scores, and a cross-O-DU LSTM-autoencoder/Isolation-Forest ensemble combines the continuous scores and signaling counters. Model fitting and threshold calibration use benign operation only. I also implement a custom E2 service model that exports per-O-DU RRC counters and O-DU MAC scheduler-outcome counters. Across ten storm scenarios, the detector obtains 0.991 PR-AUC; its recall is 0.943 at a threshold calibrated to the 95th percentile of benign scores, compared with 0.972 and 0.860 for the strongest unsupervised baseline. At the 10s operating window, cross-O-DU combination raises recall on the rolling, low-intensity coordinated scenario from 0.27 to 0.81.
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    Measuring the Severity of Violations Committed by Pedestrians at Signalized Intersections
    (University of Waterloo, 2026-10-21) Kim, Jeffrey
    Pedestrian safety remains a global concern, with pedestrians accounting for a substantial proportion of road fatalities and injuries. Previous research has examined many factors that influence pedestrian safety however, pedestrian violations at signalized intersections are a major contributor to pedestrian-vehicle conflicts, yet existing traffic safety research primarily treats these behaviours as binary outcomes, either as compliant or non-compliant. This representation fails to capture the varying degrees of severity in different crossing paths, limiting a nuanced understanding of pedestrian risk and road safety. To address this gap, this thesis proposes, applies, and evaluates continuous metrics to characterize the severity of both spatial and temporal pedestrian violations at signalized intersections. Three spatial violations (SV) metrics and four temporal violation (TV) metrics were developed. To evaluate these measures, observational pilot studies were conducted at a highly active signalized intersection in Waterloo, Ontario, utilizing both drone and street-level video data. The spatial violation analysis revealed that 48% of pedestrians committed a spatial violation, with the vast majority (86.5%) engaging in corner cutting. Among the spatial metrics, SV Metric 2 (total violation area) and SV Metric 3 (time-step metric) provided the most robust and consistent severity evaluations, whereas SV Metric 1 (maximum lateral distance) tended to overestimate spatial violation severities. The temporal violation analysis found that 7.6% of pedestrians committed a temporal violation, predominantly initiating crossings during the Flashing Don’t Walk interval (86.7%). Unlike the spatial metrics, the temporal metrics yielded statistically distinct severity distributions, demonstrating that the measurement of temporal violation severities is highly sensitive to whether the selected metric prioritizes strict legal compliance or practical safety risk. Ultimately, this research recommends the use of SV Metrics 2 and 3 for spatial analysis and provides a framework for selecting appropriate TV metrics based on specific study parameters. The proposed metrics can be integrated into existing automated traffic data collection systems, supporting future research relating violation severity to conflict severity.