High Performance PHP Garbage Collection

PHP accidentally became a programming language, and decisions in the language semantics have restricted common implementations to reference counting garbage collection. This project aims to achieve high performance garbage collection for Facebook's HipHop Virtual Machine.

My role:

For my honours project and thesis in 2015, I worked on HHVM to introduce high performance garbage collection in the form of a tracing garbage collector, using a mark-region based memory manager. PHP as a language is married to reference counting, relying on exact reference counts for copy-on-write optimisations, and relying on the destruction of objects happening at an exact moment when the reference count drops to zero, which no longer is assured when using tracing garbage collection.

Technologies used: