41815394
by sheaf at 2026-08-25T19:40:20+02:00
Driver: structured concurrent worker abstraction
This commits introduces a structured concurrency framework in the style
of the 'ki' library: a collection of threads within a scope.
We implement two kind of concurrent workers on top of this framework:
- Independent workers cannot wait for one another at all. The only
scheduling operation is to wait for quiescence.
- Coordinating workers declare an STM readiness condition (waiting on
other workers to complete) which gates their start.
See Note [Deterministic concurrent workers] in GHC.Driver.Concurrency.
This commit ports upsweep to this new framework, with downsweep being
left as subsequent work.
Further changes along the way:
- Refactoring of how concurrency is acquired to avoid the footgun of
trying to use a no-op 'AbstractSem' as a lock in the serial case.
- The "re-run with -j1" logic for semaphore opening errors no longer
triggers on late semaphore failures (part-way through a lengthy
computation).
- Logger threads are properly cleaned up on exception, with each
concurrent worker's log queue and local TmpFs properly bracketed.
- The 'GhcMessage -> AnyGhcDiagnostic' and 'Maybe Messager'
arguments of 'depanalE', 'depanalPartial' and 'downsweep', which
were all dead in practice, have been dropped.