Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC Commits: 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. - - - - - 2 changed files: - testsuite/tests/rts/T27131.hs - testsuite/tests/rts/T27131.stdout Changes: ===================================== testsuite/tests/rts/T27131.hs ===================================== @@ -30,16 +30,22 @@ foreign import ccall unsafe "has_local_stop_after_return" main :: IO () main = do setNumCapabilities 2 - checkFlag - "TSO_STOP_NEXT_BREAKPOINT" - rts_enableStopNextBreakpoint - rts_disableStopNextBreakpoint - c_hasLocalStopNextBreakpoint - checkFlag - "TSO_STOP_AFTER_RETURN" - rts_enableStopAfterReturn - rts_disableStopAfterReturn - c_hasLocalStopAfterReturn + -- Bind to capability 0 so it can't float between capabilities while the + -- target thread runs on capability 1. + doneVar <- newEmptyMVar + _ <- forkOn 0 $ do + checkFlag + "TSO_STOP_NEXT_BREAKPOINT" + rts_enableStopNextBreakpoint + rts_disableStopNextBreakpoint + c_hasLocalStopNextBreakpoint + checkFlag + "TSO_STOP_AFTER_RETURN" + rts_enableStopAfterReturn + rts_disableStopAfterReturn + c_hasLocalStopAfterReturn + putMVar doneVar () + takeMVar doneVar checkFlag :: String @@ -58,6 +64,7 @@ checkFlag label enable disable isMyThreadFlagSet = do ThreadId tid# <- forkOn 1 $ do replicateM_ 2 $ do replyVar <- takeMVar targetCheckVar + yield -- make sure we reprocess the mailbox isSet <- (/= 0) <$> isMyThreadFlagSet putMVar replyVar isSet ===================================== testsuite/tests/rts/T27131.stdout ===================================== @@ -1,6 +1,6 @@ -(0,False) +(0,True) TSO_STOP_NEXT_BREAKPOINT set: ok TSO_STOP_NEXT_BREAKPOINT unset: ok -(0,False) +(0,True) TSO_STOP_AFTER_RETURN set: ok TSO_STOP_AFTER_RETURN unset: ok View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/7ab9028865d37796a2ad3099b06eed91... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/7ab9028865d37796a2ad3099b06eed91... You're receiving this email because of your account on gitlab.haskell.org.