Severing ties: the need for non-updateable thunks
summary
Lazy thunk updates create long in-memory instruction chains and trigger expensive major GCs; duplicating thunks before pattern-matching severs those links so each evaluated copy can be collected by minor GC. The practical workaround is the dupIO package which provides non-updateable thunks via shallow copies (no deep-graph copy), is tested on GHC 8.6–9.6, removes the linked-list leak (the demo shows a 1.6 GB pipe buildup without duplication), and works but remains a low-level, hacky solution rather than a language-level fix.
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chapters (9)
- 0:00Introduction to the problem
- 1:03DSL memory leak explained
- 2:29The thunk duplication solution
- 6:20Complexities of manual copying
- 9:45GHC optimization pitfalls
- 12:34Risks of unsafe operations
- 14:00GC promotion and heap growth
- 19:19Current tools and future ideas
- 22:09Q&A and concluding remarks
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