13. Related Work

BOLT (bolt-omp.org, Best Paper PACT '19) is the closest analogue to this project. BOLT is a full OpenMP runtime built on Argobots, a lightweight user-level threading library from Argonne National Laboratory. Where libgomp maps OpenMP threads to pthreads, BOLT maps them to Argobots user-level threads (ULTs) scheduled on execution streams (ES) — achieving efficient nested parallelism and fine-grained tasking that pthreads cannot.

The architectural parallel is direct:

Concept	BOLT / Argobots	ghc-openmp / GHC RTS
OS-thread abstraction	Execution Stream (ES)	Capability
Lightweight work unit	ULT / Tasklet	Haskell green thread
OpenMP thread mapping	ULT on ES	OS thread pinned to Capability
Scheduler	Pluggable per-pool	GHC spark pool + spin-wait workers
Work stealing	Built-in	Phase 15 deferred tasks

The key difference is motivation: BOLT starts from a purpose-built threading substrate (Argobots) designed for composing HPC runtimes (MPI + OpenMP + task libraries). ghc-openmp repurposes an existing language runtime that already provides green threads, garbage collection, and an FFI — trading Argobots' generality for seamless Haskell interoperation.

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