Duncan Coutts pushed to branch wip/dcoutts/issue-27105-stopTicker at Glasgow Haskell Compiler / GHC Commits: f2f5c6ba by Nikita Efremov at 2026-06-02T16:04:54+00:00 fix typo : compete with performance, not complete - - - - - 5524ea0e by Wolfgang Jeltsch at 2026-06-03T08:01:26-04:00 Make the current `base` buildable with GHC 9.14 This comprises the following changes: * Disable some imports into `GHC.Base` for GHC 9.14 * Disable some imports into `Prelude` for GHC 9.14 * Disable separate `ArrowLoop` import for GHC 9.14 * Disable `GHC.Internal.STM` import for GHC 9.14 * Disable `GHC.Internal.Unicode.Version` import for GHC 9.14 * Disable `GHC.Internal.TH.Monad` import for GHC 9.14 * Add alternative `fixIO` import for GHC 9.14 * Add alternative `unsafeCodeCoerce` import for GHC 9.14 * Disable hiding of imported SIMD operations for GHC 9.14 * Disable use of GHC 9.14’s `printToHandleFinalizerExceptionHandler` * Enable use of `getFileHash` from `ghc-internal` for GHC 9.14 * Make `thenA` available for GHC 9.14 * Make `thenM` available for GHC 9.14 * Disable translation of `IoManagerFlagPoll` for GHC 9.14 * Add `hGetNewlineMode` for GHC 9.14 - - - - - d3438055 by Enrico Maria De Angelis at 2026-06-03T08:02:17-04:00 Fix #27067 - Clarify haddocks on `minusNaturalMaybe` - - - - - f9bcfac2 by sheaf at 2026-06-03T14:47:19-04:00 Avoid mkTick in Core Prep breaking ANF As discovered in #27182, mkTick can break ANF. This patch introduces a variant of mkTick that skips the single optimisation that could break ANF. This is preferrable over switching to the raw Tick constructor, as the latter may introduce spurious cost centres in profiling reports. This is a temporary measure until we more thoroughly refactor how mkTick works (see #27141). See Note [mkTick breaks ANF] in GHC.CoreToStg.Prep. Fixes #27182 - - - - - cf1fd661 by Artem Pelenitsyn at 2026-06-03T14:48:09-04:00 clarify comment for getSizeofMutableByteArray#: we get the size in bytes, not "elements" - - - - - a3b431f3 by David Eichmann at 2026-06-04T10:10:19+00:00 Hadrian: convert env variable ACLOCAL_PATH to unix paths. Convert ACLOCAL_PATH to a unix style path when invoking autoreconf. Autoreconf doesn't handle windows paths. See Note [Autoreconf unix paths from ACLOCAL_PATH]. Fixes #27311 - - - - - 18f6138a by Simon Jakobi at 2026-06-04T20:20:31-04:00 testsuite: Deduplicate --only test names config.only is assumed to be a set, but supplying --only overwrote it with the (list) argparse result, which can contain duplicates. When a test ran, config.only.remove(name) dropped only the first occurrence, so a duplicated name lingered and was later misreported as a "test not found" framework failure. Store it as a set instead. Fixes #27322 Co-Authored-By: Claude Opus 4.7 - - - - - 2f3cc9ff by Simon Jakobi at 2026-06-08T07:55:49-04:00 testsuite: detect fast bignum via ghc-internal, not removed ghc-bignum The ghc-bignum package was merged into ghc-internal, so the BIGNUM_GMP probe in test.mk ran `ghc-pkg field ghc-bignum exposed-modules`, which fails with "cannot find package ghc-bignum". That error went to stderr and leaked into the captured stderr of every makefile_test, causing spurious [bad stderr] failures across the suite. The probe also silently returned empty, so config.have_fast_bignum was wrongly False even on GMP builds. Probe ghc-internal's extra-libraries for the gmp library instead: the GMP backend module is an other-module (not exposed), but GMP_LIBS adds gmp to extra-libraries only on a GMP build, so this distinguishes the backends. Redirect stderr to keep any future missing-package error off the harness's stderr. This also removes a stale comment as per suggestion from hsyl20. Co-Authored-By: Claude Opus 4.7 - - - - - eb3bf6e7 by Alan Zimmerman at 2026-06-08T07:56:32-04:00 EPA: Rename Transform.anchorEof to addModuleCommentOrigDeltas This now matches what it actually does. - - - - - 498bb21a by David Eichmann at 2026-06-09T18:02:39-04:00 Hadrian: avoid response files when command line is short enough This replaces the logic of always using response files on Windows. With the new condition based on command line lenght, reponse files can be avoided in many more cases (on windows). Now that response files are only used in a small number of cases, response files are always kept and the -r / --keep-response-files command line options have been removed The response file paths are nolonger randomized. They are placed in the `_build/rsp` directory. This ensures they are ignored by git and we that Hadrian reuses response file paths when rebuilding rather than leaving stale response files around. Update user guide putting response files in its own section - - - - - 87f510a5 by Simon Hengel at 2026-06-09T18:03:25-04:00 Don't use non-breaking spaces - - - - - 41a19379 by David Eichmann at 2026-06-09T18:04:11-04:00 Hadrian: remove unused wrapper scripts from windows bindist These wrapper scripts are only installed on non-relocatable builds which are not generally supported on windows. - - - - - ce01ccb6 by sheaf at 2026-06-10T05:08:48-04:00 Don't drop ticks around variables of type `IO ()` GHC.Core.Utils.mkTick is responsible for placing a tick on a Core expression. It contains logic for dropping SCCs (non-counting profiling ticks) around non-function variables, as such variables cannot meaningfully contribute to profiles. However, the logic for what counts as a function was incorrect: it used `isFunTy` which returns 'False' for types such as 'IO ()' where the function arrow is hidden under a newtype. We now use 'mightBeFunTy' instead of 'isFunTy'. This ensures we don't drop ticks in cases we aren't sure. On the way, we improve the documentation of 'isFunTy', 'isPiTy' and 'mightBeFunTy', and update the latter's implementation to consistently handle unary classes. Fixes #27225 ------------------------- Metric Decrease: T5642 ------------------------- - - - - - d311c4f1 by Simon Jakobi at 2026-06-10T05:09:32-04:00 testsuite: Add regression test for #4081 Check that a strict constructor field is unboxed once outside an enclosing loop, not re-inspected each iteration (the float-out case-floating from 9cb20b488). Uses simonpj's `data T a = T !a` example from the ticket; T4081.stderr captures the expected Core. Co-Authored-By: Claude Opus 4.7 - - - - - 333df444 by sheaf at 2026-06-10T05:10:25-04:00 Check for cabal-install >= 3.12 upfront Starting with commit 8cb99552f607f6bc4000e45ab32532d50c8bb996, Hadrian requires cabal-install >= 3.12 in order to use the 'cabal path' command that was introduced in version 3.12, as per https://github.com/haskell/cabal/blob/a51c4ee1556d816ad86e90db7e6330dd51b0b6... This was not reflected in the Hadrian build script, causing a delayed build failure instead of enforcing the version requirement upfront, which this patch does. Fixes #27317 - - - - - 98c20394 by sheaf at 2026-06-10T05:11:09-04:00 Fix crash in Data.Data instance for HsCtxt The Data.Data instance for HsCtxt contained an error for the 'toConstr' method, which could trigger for example when looking at -ddump-tc-ast traces. Replace it with the 'abstractConstr' pattern used in the rest of the codebase. - - - - - 5ac9ce7d by Zubin Duggal at 2026-06-10T21:26:32+05:30 hadrian: Remove old package.conf files when generating new ones Old package.conf files might exists with different hashes, causing issues like #26661 Fixes #26661 - - - - - c9015f09 by sheaf at 2026-06-11T12:40:28-04:00 Fix AArch64 clobbering bug for MUL2 On AArch64, the code generator could clobber one of the input operands when computing the lower bits of a MUL2 operation. This rendered invalid the subsequent computation of the high bits. This commit fixes that by using a temporary register. The register allocator can remove the redundant move in the common case when the registers do not conflict. Fixes #27046 - - - - - 7ab90288 by Rodrigo Mesquita at 2026-06-11T12:41:11-04:00 fix: make T27131 less flaky It seems that T27131 fails flakily in a race where we check the flag before the capability had the chance to process the mailbox which sets the flag. This seemingly should only happen if the capability ends up being the same for setting and checking the flag. - - - - - 8965cb76 by Marc Scholten at 2026-06-12T04:53:22-04:00 haddock: render modules concurrently - - - - - 8cc0b64a by Duncan Coutts at 2026-06-12T04:54:06-04:00 Promote HAVE_PREEMPTION from Timer.c to OSThreads.h We will want to know about HAVE_PREEMPTION in more places. HAVE_PREEMPTION tells us that we do have OS threads available, irrespective of whether THREADED is defined. In particular, HAVE_PREEMPTION is defined on all proper OSs, but not on WASM (and hyopthetically may not be true on some other platforms like micro-controllers, RTOSs, VM hypervisors etc). - - - - - cce574ed by Duncan Coutts at 2026-06-12T04:54:06-04:00 Define ACQUIRE_LOCK_ALWAYS and friends Fix issue #27335 Like the atomic _ALWAYS variants, these lock actions are always defined, rather than being dependent on whether we are in the THREADED case. All the "normal" LOCK macros are defined to be no-ops when !THREADED. The use case for the _ALWAYS variants is where we are using OS threads even in the non-threaded RTS. This includes everything to do with the timer/ticker thread, which is used in the non-threaded RTS too. In particular, we will want to use this for eventlog things, because the timer thread performs eventlogging concurrently with the main capability, even in the non-threaded RTS. - - - - - 1f28d1f6 by Duncan Coutts at 2026-06-12T04:54:06-04:00 Use ACQUIRE/RELEASE_LOCK_ALWAYS with eventBufMutex Even in the non-threaded RTS the eventBufMutex is needed by both the main capability and the timer/ticker thread, so always use the mutex. This should fix #25165 which is about the main capability and the timer thread posting events to the eventlog buffer concurrently and thereby corrupting the buffer data. - - - - - 0ff29782 by Duncan Coutts at 2026-06-12T04:54:06-04:00 Expose eventBufMutex in the EventLog interface/header We will need it in forkProcess to ensure we don't write to the global eventlog buffer concurrently with trying to flush eventlog buffers and do the fork(). - - - - - 7a688395 by Duncan Coutts at 2026-06-12T04:54:07-04:00 Split flushAllCapsEventsBufs into safe and unlocked version Following the convention that unlocked versions have a trailing _ underscore in their name. This one requires the caller to hold the eventlog global buffer mutex. We will need this in forkProcess. - - - - - 341ed474 by Duncan Coutts at 2026-06-12T04:54:07-04:00 Remove redundant use of stopTimer in setNumCapabilities Historically, the comment here was: We must stop the interval timer while we are changing the capabilities array lest handle_tick may try to context switch an old capability. See #17289. and We must disable the timer while we do this since the tick handler may call contextSwitchAllCapabilities, which may see the capabilities array as we free it. What this refers to is that historically, when changing the number of capabilities, the array of capabilities was reallocated to a new size, allocating new ones and freeing the old ones, thus invalidating all existing capbility pointers. Strangely, for good measure the code used to call stopTimer twice (hence the two similar comments above). However, since commit a3eccf06292dd666b24606251a52da2b466a9612, the capabilities array is no longer reallocated. Instead the array is allcoated once on RTS startup to the maximum size it could ever be allowed to be, and then capabilities get enabled/disabled at runtime. So the capability pointers never become invalid anymore. At worst, they may point to capabilities that are disabled. Thus we no longer need to stop the timer (twice) while we change the number of enabled capabilities. This also partially solves issue #27105, which notes that stopTimer is being used as if it were synchronous, when it is not. At least for this case, the solution is that stopTimer is not needed at all! - - - - - 674858e3 by Duncan Coutts at 2026-06-12T04:54:07-04:00 Remove redundant use of stopTimer in forkProcess but replace it with taking the eventlog buffer lock during the fork. Fixes issue #27105 The original reason to block the timer during a fork was that historically the timer was implemented using a periodic timer signal, and the signal itself would interrupt the fork system call (returning EINTR). For large processes (where fork() takes a while) this could permanently livelock: the timer always would go off before the fork could complete, which got retried in a loop forever. The timer is no longer implemented as a unix signal, but uses threads. Thus the original problem no longer exists. The only remaining reason to block the timer tick is to prevent actions taken by the tick from interfering with the delicate process involved in fork (taking a load of locks and pausing everything). The only thing we need to do is to prevent the eventlog from being written to or flushed while the fork is taking place. To achieve this all we need to do is hold the mutex for the global eventlog buffer. This removes the last use of stopTimer that expects stopTimer to work synchronously (which it was not) and thus solves issue #27105. To be clear, we solve issue #27105 not by making stopTimer synchronous, but by eliminating the use sites that expected it to be synchronous. - - - - - eb64f6fa by Duncan Coutts at 2026-06-12T13:37:09+01:00 Add a test for thread scheduler fairness It also tests that the interval timer and context switching works. We also test that fairness is lost when the context switching interval is too coarse for the duration of the test. We add this test before doing surgery on the interval timer, so we have decent coverage. - - - - - b98680f0 by Duncan Coutts at 2026-06-12T13:37:09+01:00 Make exported stop/startTimer no-ops, and rename internal functions Specifically, internally rename: stop/startTimer to pause/unpauseTimer stop/startTicker to pause/unpauseTicker and keep stop/startTimer as exported functions, but now as no-ops. In the past the stop/startTicker actions were used incorrectly as if they were synchronous, which they are not. See issue #27105. We now document pause/unpackTicker as being async and not to be used for the purpose of concurrency safety. The existing stop/startTimer (note Timer not Ticker, the Timer calls the Ticker!) are also exported from the RTS as a public API. This was historically because the ticker used signals and it was important to suspend the timer signel over a process fork. So these functions were exported to be used by the process and unix libraries. We cannot just remove the RTS exports, but we now make them no-ops, and they can be removed from the process and unix library later. This was already documented in a changelog.d entry no-more-timer-signal but due to changes during the MR process the change to make stop/startTicker into no-ops didn't make it into the earlier MR. - - - - - c09e823b by Duncan Coutts at 2026-06-12T13:37:09+01:00 Make exitTicker/exitTimer unconditionally synchronous We never use them asynchronously, and we should never need to do so. And update some related comments. - - - - - 1d60852d by Duncan Coutts at 2026-06-12T13:37:09+01:00 posix ticker: update and improve comments on (un)pause and exit Clarify what is async vs sync. - - - - - 66997f76 by Duncan Coutts at 2026-06-12T13:37:09+01:00 posix ticker: split out ppoll/select helper functions Move the #ifdefs out of the main code body by introducing local helper functions and types, which themselves have two implementations (with a common API) based on ppoll or select. This helps improve clarity/readability. - - - - - 7e2fcac6 by Duncan Coutts at 2026-06-12T13:37:09+01:00 posix ticker: improve the implementation The existing implementation supported pausing and exiting, with the implementation of pausing reling on a mutex and condition variable. It needed to check the pause and stop shared variables on every iteration. It relies on ppoll or select, to wait on the timeout and also wait on an interrupt fd. The interrupt fd was only used for prompt exit/shutdown, and not for pausing or other notification. The pause only needed a lock and a memory operation, but the pause was not prompt. The resume used a lock, and signaling a cond var. The new implementation uses a somewhat more regular design: every notification is done by setting a shared variable and interrupting/notifying the ticker via the fd. The ticker thread does not need to check any shared variables on normal timer expiry, only when it recevies notification. This may be a micro-optimisation, but the tick occurs 100 times a second by default so any improvements in the hot path are amplified. When the ticker thread does receive notification it can check the various shared variables and update its local state. The blocking relies on using ppoll/select but without a timeout. This avoids the condition var and also allows further notifications when paused (also used for unpausing). This design can be extended with further notification types if needed by using and checking further shared vars (or making existing shared vars an enum or counter). This may be used in future for additional notifications to the ticker thread. This will likely be used to proxy wakeUpRts from a single handler context for example. And this approach, avoiding mutexes, is compatible with use from signal handlers. So overall, it's: * slightly simpler / more regular; * easier to extend with additional notifications; * probably slightly more efficient (but a micro-optimisation); * and supports calling notification from signal handlers - - - - - 6946dcf2 by Duncan Coutts at 2026-06-12T13:37:09+01:00 posix ticker: further minor local renaming for code clarity Improve the clarity with better choice of names for several local vars and function. - - - - - 1c934fcf by Duncan Coutts at 2026-06-12T13:37:09+01:00 win32 ticker: split out local helper functions - - - - - 78bf1a58 by Duncan Coutts at 2026-06-12T13:37:09+01:00 win32 ticker: provide guarantee about concurrency and idempotency Use a lock to ensure pause/unpause can be used concurrently. Use a paused variable, protected by the lock, to ensure that pause and unpause are both idempotent. This is what the portable API expects. - - - - - 89b61c10 by Duncan Coutts at 2026-06-12T13:37:09+01:00 win32 ticker: make the initial tick be after one wait interval There is no need to tick immediately. This is consistent with the posix implementation. - - - - - f78dd0e2 by Duncan Coutts at 2026-06-12T13:37:09+01:00 ticker: remove now-unnecessary layer of enable/disable There was an atomic variable used to block *part* of the actions of the tick handler. This still did not make stopTimer synchronous, even for the part of the the handle_tick actions it covered. It also added a more expensive (sequentuially consistent) atomic operation in the hot path for the handle_tick action, whereas our new design requires no atomic ops at all. Now that we have eliminate the need for synchronous stop/startTicker, we don't need this not-quite-working-anyway atomic protocol. The new pause/unpauseTicker is explicitly asynchronous and idempotent. - - - - - 4d8afd3b by Duncan Coutts at 2026-06-12T13:37:09+01:00 ticker: add TODOs about issue #27250: too much being done from handle_tick The handle_tick should not perform I/O, block, perform long-running operations or call arbitrary user code. Unfortunately, everything to do with the eventlog (at the moment) falls into all those categories. - - - - - 95 changed files: - boot - + changelog.d/T27046 - + changelog.d/T27182.md - + changelog.d/T27225 - + changelog.d/T27317 - + changelog.d/T27359 - changelog.d/hadrian-response-files.md - + changelog.d/hadrian-stale-package-confs-26661 - compiler/GHC/Builtin/primops.txt.pp - compiler/GHC/CmmToAsm/AArch64/CodeGen.hs - compiler/GHC/Core/Type.hs - compiler/GHC/Core/Utils.hs - compiler/GHC/CoreToStg/Prep.hs - compiler/GHC/Driver/Backend.hs - compiler/GHC/Hs/Instances.hs - compiler/GHC/Parser/PostProcess/Haddock.hs - compiler/GHC/Runtime/Debugger/Breakpoints.hs - compiler/GHC/Runtime/Eval/Types.hs - compiler/GHC/Runtime/Heap/Inspect.hs - compiler/GHC/Types/RepType.hs - compiler/GHC/Utils/Logger.hs - docs/users_guide/javascript.rst - docs/users_guide/using.rst - hadrian/build-cabal - hadrian/src/Builder.hs - hadrian/src/CommandLine.hs - hadrian/src/Hadrian/Builder/Ar.hs - hadrian/src/Hadrian/Haskell/Cabal/Parse.hs - hadrian/src/Hadrian/Oracles/Path.hs - hadrian/src/Hadrian/Utilities.hs - hadrian/src/Rules/BinaryDist.hs - libraries/base/src/Control/Applicative.hs - libraries/base/src/Control/Arrow.hs - libraries/base/src/Control/Monad.hs - libraries/base/src/Data/Array/Byte.hs - libraries/base/src/Data/Fixed.hs - libraries/base/src/GHC/Base.hs - libraries/base/src/GHC/Conc.hs - libraries/base/src/GHC/Conc/Sync.hs - libraries/base/src/GHC/Exts.hs - libraries/base/src/GHC/Fingerprint.hs - libraries/base/src/GHC/IO/Handle.hs - libraries/base/src/GHC/RTS/Flags.hs - libraries/base/src/GHC/Unicode.hs - libraries/base/src/GHC/Weak.hs - libraries/base/src/GHC/Weak/Finalize.hs - libraries/base/src/Prelude.hs - libraries/base/src/System/IO.hs - libraries/base/src/System/Mem/Weak.hs - libraries/ghc-internal/src/GHC/Internal/Lexeme.hs - libraries/ghc-internal/src/GHC/Internal/Natural.hs - rts/Capability.c - rts/RtsStartup.c - rts/Schedule.c - rts/Ticker.h - rts/Timer.c - rts/Timer.h - rts/eventlog/EventLog.c - rts/eventlog/EventLog.h - rts/include/rts/OSThreads.h - rts/include/rts/Timer.h - rts/posix/Ticker.c - rts/win32/Ticker.c - testsuite/driver/runtests.py - testsuite/mk/test.mk - + testsuite/tests/codeGen/should_run/T27046.hs - + testsuite/tests/codeGen/should_run/T27046_cmm.cmm - testsuite/tests/codeGen/should_run/all.T - + testsuite/tests/concurrent/should_run/T27105.hs - testsuite/tests/concurrent/should_run/all.T - testsuite/tests/count-deps/CountDepsAst.stdout - testsuite/tests/count-deps/CountDepsParser.stdout - + testsuite/tests/profiling/should_compile/T27182.hs - testsuite/tests/profiling/should_compile/all.T - + testsuite/tests/profiling/should_run/T27225.hs - + testsuite/tests/profiling/should_run/T27225.stdout - + testsuite/tests/profiling/should_run/T27225b.hs - + testsuite/tests/profiling/should_run/T27225b.stdout - testsuite/tests/profiling/should_run/all.T - testsuite/tests/profiling/should_run/caller-cc/CallerCc1.prof.sample - testsuite/tests/profiling/should_run/callstack001.stdout - testsuite/tests/profiling/should_run/scc001.prof.sample - testsuite/tests/rts/T27131.hs - testsuite/tests/rts/T27131.stdout - + testsuite/tests/simplCore/should_compile/T4081.hs - + testsuite/tests/simplCore/should_compile/T4081.stderr - testsuite/tests/simplCore/should_compile/all.T - utils/check-exact/Main.hs - utils/check-exact/Transform.hs - utils/haddock/haddock-api/haddock-api.cabal - utils/haddock/haddock-api/src/Haddock.hs - utils/haddock/haddock-api/src/Haddock/Backends/Hyperlinker.hs - utils/haddock/haddock-api/src/Haddock/Backends/Xhtml.hs - utils/haddock/haddock-api/src/Haddock/Options.hs - utils/haddock/haddock-api/src/Haddock/Utils.hs The diff was not included because it is too large. View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/50dd42dae73599ee3097174ec5fb1d7... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/50dd42dae73599ee3097174ec5fb1d7... You're receiving this email because of your account on gitlab.haskell.org.