Duncan Macgregor
Principal Software Engineer at GE Energy
Cambridge, England, United Kingdom
Summary
🤩
RockstarDuncan Macgregor is a Principal Software Engineer based in Cambridge with over a decade of experience implementing dynamic languages and low-level VM features on the JVM. Now at ServiceNow and formerly with Oracle Labs, he has deep expertise in GraalVM, TruffleRuby, and OpenJDK Loom—contributing performance-critical fixes, intrinsics, and native C-API work that bridge Ruby semantics and JVM internals. He combines hands-on Java and C development with test-driven specification work, improving string/format handling, arithmetic primitives for LLVM, and virtual-thread support. Duncan’s contributions to high-profile open-source projects like TruffleRuby, Graal, and Loom demonstrate a rare mix of language runtime design and practical engineering. Colleagues rely on him to tackle subtle edge cases and optimize cross-language interoperability in production systems.
10 years of coding experience
5 years of employment as a software developer
Stackoverflow
1reputation
0reached
0answers
0questions
Github Skills (38)
postgresql10
jvm10
graalvm10
llvm10
testing10
databases10
capi10
c1110
java10
ruby10
c1710
javas10
truffleruby10
openjdk10
database10
Programming languages (7)
Github contributions (5)
oracle/truffleruby
Jan 2017 - Sep 2022
A high performance implementation of the Ruby programming language, built on GraalVM.
Role in this project:
Back-end Developer & Java Developer
Back-end Developer & Java DeveloperContributions:1 review, 1819 commits, 154 PRs in 5 years 8 months
Contributions summary:Duncan's commits primarily involve modifications and additions to the TruffleRuby project, specifically focusing on implementing and improving core Ruby functionalities. The user implemented and maintained various native functions, like `rb_tr_sprintf`, and expanded capabilities to handle value comparisons with nil and other edge-cases. The work included refactoring various parts of the codebase and also optimizing string splitting and format processing. These changes required modifying C source files as well as working with Java code.
trufflerubyperformancegraalvmjruby
ruby/spec
Jan 2017 - Aug 2022
The Ruby Spec Suite aka ruby/spec
Role in this project:Back-end Developer & Test Automation Engineer
Back-end Developer & Test Automation EngineerContributions:153 commits in 5 years 8 months
Contributions summary:Duncan primarily contributed to the ruby/spec repository by adding and modifying specifications for various C-API functions related to string manipulation, numeric conversions, and other core Ruby functionalities. They focused on ensuring the correctness and comprehensive testing of different C-API functions. Their work involved updating existing test suites to cover edge cases and provide proper validation for specific functionalities.
ruby-gemmspecrailsrubyspec
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