Duncan Coutts pushed to branch wip/dcoutts/io-manager-selectbis at Glasgow Haskell Compiler / GHC Commits: 4e9297ea by Simon Jakobi at 2026-09-11T08:32:45-04:00 ci: Actually pass --ignore-perf-failures to the testsuite driver 684c0018d9 changed the IGNORE_PERF_FAILURES handling to append to RUNTEST_ARGS with bash array syntax, but the three use sites still expand RUNTEST_ARGS as a scalar, which yields only the first array element. The appended flag was therefore dropped in every job, so perf improvements kept failing Marge Bot batches and master pipelines, contrary to #19562. Append as a string instead, matching the existing --force-colors append in test_hadrian. Fixes #27563. Assisted-by: Claude Fable 5.1 - - - - - 4f78dfdf by Simon Jakobi at 2026-09-11T08:33:24-04:00 testsuite: Give T26537 a 1.5x compile timeout Its -fregs-graph compile step tends to time out in unoptimized builds (#27188, #27776). Assisted-by: Claude Fable 5.1 - - - - - 130286e3 by Alan Zimmerman at 2026-09-11T08:34:08-04:00 EPA: Remove ListBanana / ListParens from AnnListBrackets This is a step towards making AnnList only represent lists of items which can have either braces or layout. - - - - - a9827d13 by Simon Jakobi at 2026-09-11T18:53:32-04:00 Reject ~, UNPACK and multiplicity annotations on type data fields Only `!` was rejected so far. `~`, UNPACK and multiplicity annotations were silently accepted. None of them make sense at the type level, so restriction (R3) of Note [Type data declarations] now covers all of them. Fixes #27732. Assisted-by: Claude Fable 5.1 - - - - - c71d5e23 by Alan Zimmerman at 2026-09-11T18:54:11-04:00 EPA: Add a Note for the exact print main loop - - - - - 7a108e43 by Simon Jakobi at 2026-09-12T18:35:59-04:00 FastString: Drop mkFastStringWith's constructor callback All three callers passed the same callback, a partial application of mkNewFastStringShortByteString to the string being interned. That partial application is allocated as a closure before the table lookup, on the common hit path too, although the callback is needed only after a miss. Drop the parameter and call mkNewFastStringShortByteString directly after a miss. Since nothing is passed "with" anymore, rename the function to internSB. Suggested by Simon PJ in #27528: https://gitlab.haskell.org/ghc/ghc/-/work_items/27528#note_687031 Assisted-by: Claude Fable 5 - - - - - 82c73b22 by Alan Zimmerman at 2026-09-12T18:36:38-04:00 EPA: More targeted HsDo exact print annotation HsDo is multi-purpose, as encoded in its HsDoFlavour field. Some of these are in a layout context (DoExpr, MDoExpr), others are not (ListComp, MonadComp). We are moving towards using AnnList only in layout contexts, so we switch the HsDo TTG annotation from holding an AnnList for this, to holding Either (EpToken "[", EpToken "]") AnnList This also allows us to trim down AnnListBrackets to only have braces or None, thereby opening the door for unification with the existing layout context data type EpLayout. - - - - - 0794a23f by Duncan Coutts at 2026-09-15T09:07:30+01:00 Refactor (and rename) removeFromQueues, to simplify I/O managers Rename it to unblockAndAppendToRunQueue which better reflects what it is intended to do. The post-condition for unblockAndAppendToRunQueue is that the TSO is on the run queue or it is in the process of migrating to another cap. Previously it achieved that by always directly adding the TSO to the run queue itself. But this actually made things more complicated for the I/O managers, because it meant they needed a separate code path for notifying for cancellation compared to notifying for completion. The general notification code would always add the TSO to the run queue itself. So the improvement is to allow different cases in unblockAndAppendToRunQueue to achieve the same outcome in different ways: either directly adding to the run queue or calling helper functions that do so themselves. This then allows the new I/O managers to share code between the sync and async cancellation, and to reuse their notifyIOCompletion helpers for cancellation. This avoids a source of bugs where the completion path may be updated but the cancellation path may be forgotten, or similarly in future for sync/async operations. Update all the existing in-RTS I/O managers, and the posix timeout code. - - - - - 0576c701 by Duncan Coutts at 2026-09-15T09:07:30+01:00 Document that awaitCompletedTimeoutsOrIO expects an empty run queue This was true before but implicit and not relied on much. It's better to be explicit, and allow things to depend on it. - - - - - 3bff01ae by Duncan Coutts at 2026-09-15T09:07:30+01:00 Store the I/O opcode and fd in the StgAsyncIOOp This will be useful in several I/O managers and it is handy for logging and debugging. It also doesn't increase the size of the StgAsyncIOOp structure. There was enough spare padding space already. Update the poll I/O manager to set the new fields. Add a helper function to convert the enum IOReadOrWrite into the enum IOOpCode. Also change IOReadOrWrite to be an enum without a typedef, for consistency with other enumerations in IOManager.h - - - - - 29f0905b by Duncan Coutts at 2026-09-15T09:07:30+01:00 Add a new I/O manager based on select() Yes, this is the second such I/O manager, but it is a modern re-implementation based on the new in-RTS I/O manager infrastructure. So it is cleaner and faster than the old select I/O manager. Why do we need another I/O manager based on select? Why isn't the poll() one good enough as a baseline portable unix I/O manager? Because macOS. Apple Inc. is why we cannot have nice things. The man page for poll on macOS documents the fact that it does not work. At least, it does not work for all files. Specifically, it does not work for device files. Whereas macOS select() does work for device files. Aaaaarg! We _do_ want to deprecate and remove the old select I/O manager, but due to macOS we cannot do that until we have a replacement. This is that replacement. Until of course a nice new k-queue I/O manager arrives, which could become the new default for macOS and FreeBSD. Interestingly, this select I/O manager is actually faster than the poll one, on Linix, in some circumstances: specifically when many Haskell threads are waiting on the same fd. The poll I/O manager does O(n) work for n threads waiting on I/O, whereas the select one does O(fds) work for the number of fds that threads are waiting on. Usually this is 1:1, so it's not noticable, but one can concoct extreme benchmarks to show the difference. - - - - - 5c4fc551 by Duncan Coutts at 2026-09-15T09:07:30+01:00 Minor updates in the poll I/O manager to keep in sync with select This keeps it in sync with select one. The changes are based on code review while implementing the new select I/O manager. The two I/O managers are so similar in structure that it makes sense to try to minimise the diff between them. This should aid understanding, and fixes to both in future. - - - - - aaf0ab42 by Duncan Coutts at 2026-09-15T09:07:30+01:00 Document the new select I/O manager in the user guide in the RTS section about I/O managers. And add a changelog entry. - - - - - 54 changed files: - .gitlab/ci.sh - + changelog.d/27732 - + changelog.d/select-io-manager - compiler/GHC/Data/FastString.hs - compiler/GHC/Hs/Expr.hs - compiler/GHC/Hs/Pat.hs - compiler/GHC/Hs/Utils.hs - compiler/GHC/Parser.y - compiler/GHC/Parser/Annotation.hs - compiler/GHC/Parser/PostProcess.hs - compiler/GHC/Rename/Module.hs - compiler/GHC/Tc/Errors/Types.hs - docs/users_guide/exts/type_data.rst - docs/users_guide/runtime_control.rst - libraries/base/src/GHC/RTS/Flags.hs - libraries/ghc-internal/src/GHC/Internal/RTS/Flags.hsc - rts/IOManager.c - rts/IOManager.h - rts/IOManagerInternals.h - rts/RaiseAsync.c - rts/configure.ac - rts/include/rts/Flags.h - rts/include/rts/storage/Closures.h - rts/posix/Poll.c - rts/posix/Poll.h - + rts/posix/SelectBis.c - + rts/posix/SelectBis.h - rts/posix/Timeout.c - rts/posix/Timeout.h - rts/rts.cabal - testsuite/tests/codeGen/should_run/all.T - testsuite/tests/ghc-api/T25121_status.stdout - testsuite/tests/interface-stability/ghc-experimental-exports.stdout - testsuite/tests/interface-stability/ghc-experimental-exports.stdout-mingw32 - testsuite/tests/parser/should_compile/DumpParsedAstComments.stderr - testsuite/tests/parser/should_compile/DumpSemis.stderr - testsuite/tests/printer/Test20297.stdout - + testsuite/tests/type-data/should_fail/T27732a.hs - + testsuite/tests/type-data/should_fail/T27732a.stderr - + testsuite/tests/type-data/should_fail/T27732b.hs - + testsuite/tests/type-data/should_fail/T27732b.stderr - + testsuite/tests/type-data/should_fail/T27732c.hs - + testsuite/tests/type-data/should_fail/T27732c.stderr - + testsuite/tests/type-data/should_fail/T27732d.hs - + testsuite/tests/type-data/should_fail/T27732d.stderr - + testsuite/tests/type-data/should_fail/T27732e.hs - + testsuite/tests/type-data/should_fail/T27732e.stderr - + testsuite/tests/type-data/should_fail/T27732f.hs - + testsuite/tests/type-data/should_fail/T27732f.stderr - testsuite/tests/type-data/should_fail/TDStrictnessGADT.stderr - testsuite/tests/type-data/should_fail/TDStrictnessH98.stderr - testsuite/tests/type-data/should_fail/all.T - utils/check-exact/ExactPrint.hs - utils/check-exact/Utils.hs The diff was not included because it is too large. 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