Stefan Marr
Full Professor (Universitätsprofessor) at Johannes Kepler Universität Linz
Canterbury, England, Austria
Summary
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Top SchoolStefan Marr is a Full Professor and researcher with 18 years of experience specializing in concurrency, language implementation, and virtual machine technology. Currently based in Canterbury and appointed at Johannes Kepler Universität Linz, he combines academic leadership with hands-on systems work born from a PhD at Vrije Universiteit Brussel. His practical impact includes substantive performance and code-simplicity contributions to TruffleRuby on GraalVM—optimizing string operations and adding compilation-time instrumentation—demonstrating an unusual blend of deep theory and production-grade performance engineering. Known for improving VM internals and developer tooling, he brings both teaching and engineering rigor to complex runtime challenges.
18 years of coding experience
Master, Master at Universität PotsdamDoctor of Philosophy (PhD), Doctor of Philosophy (PhD) at Vrije Universiteit BrusselBachelor, Bachelor at University of Potsdam
German, English, Dutch
Stackoverflow
835reputation
36kreached
11answers
10questions
Github Skills (14)
javas10
truffle10
performance-optimization10
graalvm10
java10
ruby10
exceptions6
php6
openssl6
parent6
traits6
inheritance6
garbage-collection6
6
Programming languages (20)
Github contributions (5)
oracle/truffleruby
Sep 2021 - Aug 2022
A high performance implementation of the Ruby programming language, built on GraalVM.
Role in this project:
Back-end Developer & Performance Engineer
Back-end Developer & Performance EngineerContributions:8 reviews, 17 commits, 8 PRs in 11 months
Contributions summary:Stefan primarily focused on performance optimization and code simplification within the TruffleRuby project. They made several changes to improve the efficiency of string operations by unwrapping ropes and modifying the string comparison logic. Additionally, they added a feature to measure the total compilation time using the CompilationMXBean and improved the code structure in other areas like frame slot management and the parsing process. Moreover, the user adapted the MacPorts heuristic to find OpenSSL 1.1 and fixed lint errors.
trufflerubyperformancegraalvmjruby
smarr/awfy-runs
Oct 2016 - Sep 2022
Contributions:32 pushes, 4 branches in 5 years 11 months
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