mozilla/rhino
Nov 2024 – Mar 2026
17 Months active
Languages Used
JavaJavaScriptGradlepropertiesGroovy
Technical Skills
Java DevelopmentObject-Oriented DesignBenchmarkingCode RefactoringData StructuresInterpreter Design
Duncan MacGregor
PROFILE
Duncan Macgregor
Over 17 months, contributed to the mozilla/rhino repository by modernizing the JavaScript engine’s core architecture, focusing on performance, correctness, and ECMAScript compliance. Delivered features such as a descriptor-driven scope and context overhaul, thread-safe slot maps, and modular interpreter refactors, while addressing concurrency, memory optimization, and debugging. Enhanced the engine’s API surface, improved test automation, and expanded support for BigInt, TypedArrays, and XML parsing. Leveraged Java, JavaScript, and Gradle to implement robust benchmarking, code generation, and build automation. The work emphasized maintainability, reduced technical debt, and enabled scalable, spec-aligned enhancements for embedded and production JavaScript environments.
Overall Statistics
Feature vs Bugs
80%Features
Repository Contributions
97Total
Bugs
9
Commits
97
Features
35
Lines of code
39,053
Activity Months17
Your Network
54 peopleWork History
March 2026
3 Commits • 2 Features
Mar 1, 2026March 2026: Focused on ES spec alignment, descriptor-driven refactors, and runtime consolidation for mozilla/rhino. Delivered descriptor-based XML handling and RegExp refactor, plus ECMAScript-compliant globalThis initialization. The changes reduce legacy class clutter, improve performance, and establish a robust foundation for future ES feature support.
3 Commits • 2 Features
Mar 1, 2026March 2026: Focused on ES spec alignment, descriptor-driven refactors, and runtime consolidation for mozilla/rhino. Delivered descriptor-based XML handling and RegExp refactor, plus ECMAScript-compliant globalThis initialization. The changes reduce legacy class clutter, improve performance, and establish a robust foundation for future ES feature support.
March 2026
February 2026
7 Commits • 2 Features
Feb 1, 2026February 2026 was defined by stability, correctness, and code quality improvements in the Rhino project. The team delivered targeted fixes and enhancements with a clear focus on business value: more reliable builds, correct runtime behavior, and stronger test coverage aligned with ECMAScript specifications. This cycle reduced CI flakiness, fixed core prototype/scope handling, and expanded test configuration for greater reliability and maintainability.
February 2026
7 Commits • 2 Features
Feb 1, 2026February 2026 was defined by stability, correctness, and code quality improvements in the Rhino project. The team delivered targeted fixes and enhancements with a clear focus on business value: more reliable builds, correct runtime behavior, and stronger test coverage aligned with ECMAScript specifications. This cycle reduced CI flakiness, fixed core prototype/scope handling, and expanded test configuration for greater reliability and maintainability.
January 2026
9 Commits • 5 Features
Jan 1, 2026January 2026 focused on delivering architectural improvements and feature parity with modern JavaScript to bolster Rhino's reliability in embedded environments. Key outcomes include safer scope management, a more robust built-ins API, BigInt support in DataView for large-number data processing, descriptor-based initialization for core objects to improve maintainability, and expanded XML parsing capabilities for schema-driven data interchange. These changes reduce maintenance costs, enable richer data processing, and improve integration with modern JS engines and applications.
9 Commits • 5 Features
Jan 1, 2026January 2026 focused on delivering architectural improvements and feature parity with modern JavaScript to bolster Rhino's reliability in embedded environments. Key outcomes include safer scope management, a more robust built-ins API, BigInt support in DataView for large-number data processing, descriptor-based initialization for core objects to improve maintainability, and expanded XML parsing capabilities for schema-driven data interchange. These changes reduce maintenance costs, enable richer data processing, and improve integration with modern JS engines and applications.
January 2026
December 2025
12 Commits • 2 Features
Dec 1, 2025December 2025 was focused on performance, correctness, and developer experience for mozilla/rhino. Key achievements include a foundational overhaul of the engine's scope, context, and environment with a new scope hierarchy and top-level context, improving variable scoping, property access, and global handling. Debugger enhancements delivered clearer local variable disambiguation, default interfaces, and a proxy-based local access mechanism, reducing runtime overhead by removing activation frames. A critical fix to this binding semantics introduced a dedicated getThisObj pathway to ensure correct global context in strict and non-strict modes across realms. Global/globalThis alignment was verified through tests. These efforts reduce runtime surprises, enable safer future optimizations, and improve developer productivity.
December 2025
12 Commits • 2 Features
Dec 1, 2025December 2025 was focused on performance, correctness, and developer experience for mozilla/rhino. Key achievements include a foundational overhaul of the engine's scope, context, and environment with a new scope hierarchy and top-level context, improving variable scoping, property access, and global handling. Debugger enhancements delivered clearer local variable disambiguation, default interfaces, and a proxy-based local access mechanism, reducing runtime overhead by removing activation frames. A critical fix to this binding semantics introduced a dedicated getThisObj pathway to ensure correct global context in strict and non-strict modes across realms. Global/globalThis alignment was verified through tests. These efforts reduce runtime surprises, enable safer future optimizations, and improve developer productivity.
November 2025
3 Commits • 3 Features
Nov 1, 2025Monthly summary for 2025-11 focusing on Rhino repository contributions. Key refactors and API improvements were delivered to reduce technical debt, boost performance, and prepare for scalable future changes. The work emphasizes business value through more maintainable code, cleaner Java integration paths, and faster internal property handling, supporting longer-term product velocity.
3 Commits • 3 Features
Nov 1, 2025Monthly summary for 2025-11 focusing on Rhino repository contributions. Key refactors and API improvements were delivered to reduce technical debt, boost performance, and prepare for scalable future changes. The work emphasizes business value through more maintainable code, cleaner Java integration paths, and faster internal property handling, supporting longer-term product velocity.
November 2025
October 2025
6 Commits • 2 Features
Oct 1, 2025October 2025 mozilla/rhino: Delivered foundational engine modularization, correctness fixes, and reliability improvements that reduce risk and prepare for scope-related work. Key features include internal engine refactoring to separate immutable code and descriptors (JSCode/JSFunction/JSScript) with centralized mapping from native code to built-ins, and enhanced testing/build reliability through new smoke tests and build stability fixes. Major bugs fixed include correctness fixes in the compiled-mode evaluation order for bitwise/arithmetic/unsigned-right-shift operations and Symbol() argument handling to align with ECMAScript specs. Overall impact includes reduced runtime defects, improved maintainability, and stronger deployment reliability. Technologies/skills demonstrated include Java, Rhino engine internals, ES specification alignment, modular refactoring, test automation, and Maven/shadow-jar maintenance.
October 2025
6 Commits • 2 Features
Oct 1, 2025October 2025 mozilla/rhino: Delivered foundational engine modularization, correctness fixes, and reliability improvements that reduce risk and prepare for scope-related work. Key features include internal engine refactoring to separate immutable code and descriptors (JSCode/JSFunction/JSScript) with centralized mapping from native code to built-ins, and enhanced testing/build reliability through new smoke tests and build stability fixes. Major bugs fixed include correctness fixes in the compiled-mode evaluation order for bitwise/arithmetic/unsigned-right-shift operations and Symbol() argument handling to align with ECMAScript specs. Overall impact includes reduced runtime defects, improved maintainability, and stronger deployment reliability. Technologies/skills demonstrated include Java, Rhino engine internals, ES specification alignment, modular refactoring, test automation, and Maven/shadow-jar maintenance.
September 2025
1 Commits • 1 Features
Sep 1, 2025September 2025 monthly summary for mozilla/rhino focused on improving observability and diagnostics in the ClassFileWriter path. The primary value delivered this month was enhanced debugging capabilities that enable faster diagnosis of code-generation issues, contributing to maintainability and developer productivity. No major bug fixes were recorded in this period; the emphasis was on strengthening the debugging surface and observability to reduce downstream debugging effort.
1 Commits • 1 Features
Sep 1, 2025September 2025 monthly summary for mozilla/rhino focused on improving observability and diagnostics in the ClassFileWriter path. The primary value delivered this month was enhanced debugging capabilities that enable faster diagnosis of code-generation issues, contributing to maintainability and developer productivity. No major bug fixes were recorded in this period; the emphasis was on strengthening the debugging surface and observability to reduce downstream debugging effort.
September 2025
August 2025
3 Commits • 1 Features
Aug 1, 2025Monthly summary for 2025-08 focusing on correctness of function binding and robustness in multi-threaded execution for mozilla/rhino. Delivered two critical updates: (1) fix for Function.prototype.call and Function.prototype.apply binding and this-context handling, including edge cases with nested apply calls; (2) thread-safety hardening for slot map operations via compound operations, refactoring locking and property definitions. These changes preserve core functionality while significantly reducing race conditions in multi-threaded environments. Improvements are supported by added tests covering bound arguments, this binding, and interpreter interactions. Impact: more predictable behavior in embedded JS runtimes, improved stability for customers running Rhino in concurrent scenarios. Technologies/skills: advanced JavaScript binding semantics, concurrency patterns, lock-based synchronization, interpreter adjustments, and test coverage.
August 2025
3 Commits • 1 Features
Aug 1, 2025Monthly summary for 2025-08 focusing on correctness of function binding and robustness in multi-threaded execution for mozilla/rhino. Delivered two critical updates: (1) fix for Function.prototype.call and Function.prototype.apply binding and this-context handling, including edge cases with nested apply calls; (2) thread-safety hardening for slot map operations via compound operations, refactoring locking and property definitions. These changes preserve core functionality while significantly reducing race conditions in multi-threaded environments. Improvements are supported by added tests covering bound arguments, this binding, and interpreter interactions. Impact: more predictable behavior in embedded JS runtimes, improved stability for customers running Rhino in concurrent scenarios. Technologies/skills: advanced JavaScript binding semantics, concurrency patterns, lock-based synchronization, interpreter adjustments, and test coverage.
July 2025
1 Commits • 1 Features
Jul 1, 2025July 2025 highlights for mozilla/rhino: Key feature delivered was an Interpreter Numeric Operations Performance Enhancement that reduces boxing/unboxing of numbers during arithmetic and bitwise operations and enables direct operations on primitive numbers where possible, resulting in faster number processing and improved interpreter speed. No major bugs fixed in this repository this month. Overall impact: lower latency for numeric-heavy Rhino scripts and improved scalability of numeric workloads. This work demonstrates strong proficiency in JVM-based performance tuning, JavaScript engine internals, and careful refactoring to preserve compatibility while improving throughput. Technologies demonstrated include Java, Rhino internals, boxing/unboxing optimization, and performance profiling.
1 Commits • 1 Features
Jul 1, 2025July 2025 highlights for mozilla/rhino: Key feature delivered was an Interpreter Numeric Operations Performance Enhancement that reduces boxing/unboxing of numbers during arithmetic and bitwise operations and enables direct operations on primitive numbers where possible, resulting in faster number processing and improved interpreter speed. No major bugs fixed in this repository this month. Overall impact: lower latency for numeric-heavy Rhino scripts and improved scalability of numeric workloads. This work demonstrates strong proficiency in JVM-based performance tuning, JavaScript engine internals, and careful refactoring to preserve compatibility while improving throughput. Technologies demonstrated include Java, Rhino internals, boxing/unboxing optimization, and performance profiling.
July 2025
June 2025
32 Commits • 7 Features
Jun 1, 2025June 2025 monthly summary for mozilla/rhino: Focused delivery on interpreter instrumentation and bytecode extraction to enable deeper runtime analytics, benchmarking, and maintainability. The team advanced V8 RegExp benchmarking integration and established a comprehensive Bytecode Extraction Framework, enabling systematic extraction of a broad set of interpreter bytecodes. Additional targeted bytecode extraction work expanded naming, typeof, and error/flow-driven bytecodes, alongside a major refactor to the main loop for readability and performance. These efforts create a solid foundation for performance optimization, easier diagnosis, and alignment with cross-engine benchmarking goals.
June 2025
32 Commits • 7 Features
Jun 1, 2025June 2025 monthly summary for mozilla/rhino: Focused delivery on interpreter instrumentation and bytecode extraction to enable deeper runtime analytics, benchmarking, and maintainability. The team advanced V8 RegExp benchmarking integration and established a comprehensive Bytecode Extraction Framework, enabling systematic extraction of a broad set of interpreter bytecodes. Additional targeted bytecode extraction work expanded naming, typeof, and error/flow-driven bytecodes, alongside a major refactor to the main loop for readability and performance. These efforts create a solid foundation for performance optimization, easier diagnosis, and alignment with cross-engine benchmarking goals.
May 2025
7 Commits • 3 Features
May 1, 2025May 2025 Rhino repository summary: focused on stabilizing test infrastructure, tightening benchmarking reliability, and extending spec-aligned capabilities, while addressing key performance and correctness regressions.
7 Commits • 3 Features
May 1, 2025May 2025 Rhino repository summary: focused on stabilizing test infrastructure, tightening benchmarking reliability, and extending spec-aligned capabilities, while addressing key performance and correctness regressions.
May 2025
April 2025
2 Commits • 1 Features
Apr 1, 2025April 2025: Delivered key modernization and reliability improvements for the Rhino project. Implemented a lambda-based refactor to modernize core JavaScript functions and fixed a critical interpreter issue related to constant initialization. These changes improve maintainability, readability, and establish a solid foundation for future performance improvements, complemented by tests and benchmarks to validate progress.
April 2025
2 Commits • 1 Features
Apr 1, 2025April 2025: Delivered key modernization and reliability improvements for the Rhino project. Implemented a lambda-based refactor to modernize core JavaScript functions and fixed a critical interpreter issue related to constant initialization. These changes improve maintainability, readability, and establish a solid foundation for future performance improvements, complemented by tests and benchmarks to validate progress.
March 2025
2 Commits • 1 Features
Mar 1, 2025March 2025: Rhino engine core modernization focusing on NativeObject and NativeArray. Migrated NativeObject and NativeArray to lambda constructors, improving spec compliance, readability, and performance. Reorganized internal object/array handling by relocating length to BuiltInSlot, introducing ArraySpeciesCreate for array operations, and enabling lazy initialization of unscopable properties for better startup performance and maintainability. Prepared groundwork for future optimizations and API evolution.
2 Commits • 1 Features
Mar 1, 2025March 2025: Rhino engine core modernization focusing on NativeObject and NativeArray. Migrated NativeObject and NativeArray to lambda constructors, improving spec compliance, readability, and performance. Reorganized internal object/array handling by relocating length to BuiltInSlot, introducing ArraySpeciesCreate for array operations, and enabling lazy initialization of unscopable properties for better startup performance and maintainability. Prepared groundwork for future optimizations and API evolution.
March 2025
February 2025
1 Commits • 1 Features
Feb 1, 2025February 2025 — Rhino repository: Core refactor to enhance concurrency safety and performance. Delivered a thread-safe Slot Map refactor (removing SlotMapContainer), introduced new thread-safe map types and a lock-aware interface. These changes simplify management, reduce runtime overhead, and provide a scalable foundation for concurrent operations. No user-facing features this month, but significant technical improvements that enable higher throughput and easier maintenance.
February 2025
1 Commits • 1 Features
Feb 1, 2025February 2025 — Rhino repository: Core refactor to enhance concurrency safety and performance. Delivered a thread-safe Slot Map refactor (removing SlotMapContainer), introduced new thread-safe map types and a lock-aware interface. These changes simplify management, reduce runtime overhead, and provide a scalable foundation for concurrent operations. No user-facing features this month, but significant technical improvements that enable higher throughput and easier maintenance.
January 2025
4 Commits • 1 Features
Jan 1, 2025January 2025 mozilla/rhino: Delivered a comprehensive interpreter architecture overhaul focused on immutability, memory efficiency, and modularity. Implemented an immutable CallFrame stack, introduced a slot-map-based memory model (SlotMapOwner, SingleEntrySlotMap), and created a modular execution loop via InterpreterResult and related classes to improve readability and maintainability. Refactored the core loop into a separate function to enhance testability and future extension. This work establishes a safer, more maintainable foundation for performance improvements and easier future refactors in the Rhino interpreter.
4 Commits • 1 Features
Jan 1, 2025January 2025 mozilla/rhino: Delivered a comprehensive interpreter architecture overhaul focused on immutability, memory efficiency, and modularity. Implemented an immutable CallFrame stack, introduced a slot-map-based memory model (SlotMapOwner, SingleEntrySlotMap), and created a modular execution loop via InterpreterResult and related classes to improve readability and maintainability. Refactored the core loop into a separate function to enhance testability and future extension. This work establishes a safer, more maintainable foundation for performance improvements and easier future refactors in the Rhino interpreter.
January 2025
December 2024
3 Commits • 1 Features
Dec 1, 2024December 2024 monthly summary focused on stability and performance improvements for mozilla/rhino. Delivered two critical items: (1) a HashSlotMap copy/resize integrity fix to prevent linked-list corruption by nullifying next and orderedNext during slot copies, and (2) performance enhancements including parameterized benchmarking for interpreted vs compiled modes and a refactor to extract the doCallByteCode path from the interpreter loop to boost runtime efficiency. These efforts reduce risk in core data structures, improve benchmarking clarity, and yield measurable runtime improvements for typical JavaScript workloads.
December 2024
3 Commits • 1 Features
Dec 1, 2024December 2024 monthly summary focused on stability and performance improvements for mozilla/rhino. Delivered two critical items: (1) a HashSlotMap copy/resize integrity fix to prevent linked-list corruption by nullifying next and orderedNext during slot copies, and (2) performance enhancements including parameterized benchmarking for interpreted vs compiled modes and a refactor to extract the doCallByteCode path from the interpreter loop to boost runtime efficiency. These efforts reduce risk in core data structures, improve benchmarking clarity, and yield measurable runtime improvements for typical JavaScript workloads.
November 2024
1 Commits • 1 Features
Nov 1, 2024Month: 2024-11 — Mozilla Rhino: SlotMap Optimization (EmptySlotMap) Key outcomes: - Implemented EmptySlotMap and empty-map initialization to optimize memory usage and avoid unnecessary object creation when no slots exist. Ensured SlotMapContainer initializes with an empty map if the initial size is 0. - Updated the checkMapSize method to handle transitions from an empty map to an embedded map, improving robustness in empty-state handling. Impact: - Reduces memory footprint and allocation overhead in sparsely populated SlotMaps, contributing to faster startup and lower GC pressure in Rhino deployments. Business value: - Delivers tangible performance gains for Rhino users with sparse datasets and improves initialization performance without impacting existing APIs. Technologies/skills demonstrated: - Java data structures; memory optimization patterns; conditional initialization; code refactoring; commit-driven development.
1 Commits • 1 Features
Nov 1, 2024Month: 2024-11 — Mozilla Rhino: SlotMap Optimization (EmptySlotMap) Key outcomes: - Implemented EmptySlotMap and empty-map initialization to optimize memory usage and avoid unnecessary object creation when no slots exist. Ensured SlotMapContainer initializes with an empty map if the initial size is 0. - Updated the checkMapSize method to handle transitions from an empty map to an embedded map, improving robustness in empty-state handling. Impact: - Reduces memory footprint and allocation overhead in sparsely populated SlotMaps, contributing to faster startup and lower GC pressure in Rhino deployments. Business value: - Delivers tangible performance gains for Rhino users with sparse datasets and improves initialization performance without impacting existing APIs. Technologies/skills demonstrated: - Java data structures; memory optimization patterns; conditional initialization; code refactoring; commit-driven development.
November 2024
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Quality Metrics
Correctness90.8%
Maintainability88.2%
Architecture86.4%
Performance76.8%
AI Usage22.8%
Skills & Technologies
Programming Languages
GradleGroovyJavaJavaScriptproperties
Technical Skills
API DevelopmentBenchmarkingBuild AutomationBuild ManagementBuild ScriptingBuild SystemsBytecode EngineeringBytecode ExecutionBytecode ImplementationBytecode InterpretationBytecode ManipulationBytecode manipulationCode CompilationCode GenerationCode Optimization
Repositories Contributed To
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