Rodrigo Mesquita pushed to branch wip/romes/27131 at Glasgow Haskell Compiler / GHC Commits: 0fb3ee21 by Rodrigo Mesquita at 2026-04-01T17:25:51+01:00 New rts Message to {set,unset} TSO flags This commit introduces stg_MSG_SET_TSO_FLAG_info and stg_MSG_UNSET_TSO_FLAG_info, which allows setting flags of a TSO other than yourself. This is especially useful/necessary to set breakpoints and toggle breakpoints of different threads, which is needed to safely implement features like pausing, toggling step-out, toggling step-in per thread, etc. Fixes #27131 - - - - - 2e6b37c7 by Rodrigo Mesquita at 2026-04-01T17:55:51+01:00 test: Add test setting another TSO's flags Introduces a test that runs on two capabilities. The main thread running on Capability 0 sets the flags on a TSO running on Capability 1. The TSO from Capability 1 itself checks whether its flags were set and reports that back. This validates that the RTS messages for setting TSO flags work, even if it doesn't test a harsher scenario with race conditions to exercise why the message passing is necessary for safely setting another TSO's flags. Part of #27131 - - - - - 11 changed files: - rts/Interpreter.c - rts/Messages.c - rts/StgMiscClosures.cmm - rts/Threads.c - rts/Threads.h - rts/include/rts/storage/Closures.h - rts/include/stg/MiscClosures.h - + testsuite/tests/rts/T27131.hs - + testsuite/tests/rts/T27131.stdout - + testsuite/tests/rts/T27131_c.c - testsuite/tests/rts/all.T Changes: ===================================== rts/Interpreter.c ===================================== @@ -416,12 +416,22 @@ void rts_disableStopNextBreakpointAll(void) void rts_enableStopNextBreakpoint(StgTSO* tso) { - tso->flags |= TSO_STOP_NEXT_BREAKPOINT; +#if defined(THREADED_RTS) + Capability* cap = rts_unsafeGetMyCapability(); + setThreadFlag(cap, tso, TSO_STOP_NEXT_BREAKPOINT); +#else + tso->flags |= TSO_STOP_NEXT_BREAKPOINT; +#endif } void rts_disableStopNextBreakpoint(StgTSO* tso) { - tso->flags &= ~TSO_STOP_NEXT_BREAKPOINT; +#if defined(THREADED_RTS) + Capability* cap = rts_unsafeGetMyCapability(); + unsetThreadFlag(cap, tso, TSO_STOP_NEXT_BREAKPOINT); +#else + tso->flags &= ~TSO_STOP_NEXT_BREAKPOINT; +#endif } /* --------------------------------------------------------------------------- @@ -430,12 +440,22 @@ void rts_disableStopNextBreakpoint(StgTSO* tso) void rts_enableStopAfterReturn(StgTSO* tso) { +#if defined(THREADED_RTS) + Capability* cap = rts_unsafeGetMyCapability(); + setThreadFlag(cap, tso, TSO_STOP_AFTER_RETURN); +#else tso->flags |= TSO_STOP_AFTER_RETURN; +#endif } void rts_disableStopAfterReturn(StgTSO* tso) { +#if defined(THREADED_RTS) + Capability* cap = rts_unsafeGetMyCapability(); + unsetThreadFlag(cap, tso, TSO_STOP_AFTER_RETURN); +#else tso->flags &= ~TSO_STOP_AFTER_RETURN; +#endif } /* ===================================== rts/Messages.c ===================================== @@ -35,7 +35,9 @@ void sendMessage(Capability *from_cap, Capability *to_cap, Message *msg) i != &stg_MSG_TRY_WAKEUP_info && i != &stg_IND_info && // can happen if a MSG_BLACKHOLE is revoked i != &stg_WHITEHOLE_info && - i != &stg_MSG_CLONE_STACK_info) { + i != &stg_MSG_CLONE_STACK_info && + i != &stg_MSG_SET_TSO_FLAG_info && + i != &stg_MSG_UNSET_TSO_FLAG_info) { barf("sendMessage: %p", i); } } @@ -137,6 +139,16 @@ loop: MessageCloneStack *cloneStackMessage = (MessageCloneStack*) m; handleCloneStackMessage(cap, cloneStackMessage); } + else if(i == &stg_MSG_SET_TSO_FLAG_info){ + MessageUpdTSOFlag *u = (MessageUpdTSOFlag*) m; + u->tso->flags |= u->flag; + return; + } + else if(i == &stg_MSG_UNSET_TSO_FLAG_info){ + MessageUpdTSOFlag *u = (MessageUpdTSOFlag*) m; + u->tso->flags &= ~u->flag; + return; + } else { barf("executeMessage: %p", i); ===================================== rts/StgMiscClosures.cmm ===================================== @@ -855,6 +855,12 @@ INFO_TABLE_CONSTR(stg_MSG_NULL,1,0,0,PRIM,"MSG_NULL","MSG_NULL") INFO_TABLE_CONSTR(stg_MSG_CLONE_STACK,3,0,0,PRIM,"MSG_CLONE_STACK","MSG_CLONE_STACK") { ccall pbarf("stg_MSG_CLONE_STACK object (%p) entered!", R1 "ptr") never returns; } +INFO_TABLE_CONSTR(stg_MSG_SET_TSO_FLAG,2,1,0,PRIM,"MSG_SET_TSO_FLAG","MSG_SET_TSO_FLAG") +{ foreign "C" barf("stg_MSG_SET_TSO_FLAG object (%p) entered!", R1) never returns; } + +INFO_TABLE_CONSTR(stg_MSG_UNSET_TSO_FLAG,2,1,0,PRIM,"MSG_UNSET_TSO_FLAG","MSG_UNSET_TSO_FLAG") +{ foreign "C" barf("stg_MSG_UNSET_TSO_FLAG object (%p) entered!", R1) never returns; } + /* ---------------------------------------------------------------------------- END_TSO_QUEUE ===================================== rts/Threads.c ===================================== @@ -376,6 +376,38 @@ migrateThread (Capability *from, StgTSO *tso, Capability *to) tryWakeupThread(from, tso); } +/* ---------------------------------------------------------------------------- + {set,unset}ThreadFlag + + sets or unsets a flag in a given TSO + ------------------------------------------------------------------------- */ + +#if defined(THREADED_RTS) +static void +updThreadFlag(Capability *from, StgTSO *tso, StgWord32 flag, const StgInfoTable* info); + +void setThreadFlag(Capability *from, StgTSO *tso, StgWord32 flag) +{ + updThreadFlag(from, tso, flag, &stg_MSG_SET_TSO_FLAG_info); +} + +void unsetThreadFlag(Capability *from, StgTSO *tso, StgWord32 flag) +{ + updThreadFlag(from, tso, flag, &stg_MSG_UNSET_TSO_FLAG_info); +} + +static void +updThreadFlag(Capability *from, StgTSO *tso, StgWord32 flag, const StgInfoTable* info) +{ + MessageUpdTSOFlag *msg; + msg = (MessageUpdTSOFlag *)allocate(from,sizeofW(MessageUpdTSOFlag)); + msg->tso = tso; + msg->flag = flag; + SET_HDR_RELEASE(msg, info, CCS_SYSTEM); + sendMessage(from, tso->cap, (Message*)msg); +} +#endif + /* ---------------------------------------------------------------------------- awakenBlockedQueue ===================================== rts/Threads.h ===================================== @@ -19,6 +19,11 @@ void checkBlockingQueues (Capability *cap, StgTSO *tso); void tryWakeupThread (Capability *cap, StgTSO *tso); void migrateThread (Capability *from, StgTSO *tso, Capability *to); +#if defined(THREADED_RTS) +void setThreadFlag (Capability *from, StgTSO *tso, StgWord32 flag); +void unsetThreadFlag (Capability *from, StgTSO *tso, StgWord32 flag); +#endif + // Wakes up a thread on a Capability (probably a different Capability // from the one held by the current Task). // ===================================== rts/include/rts/storage/Closures.h ===================================== @@ -620,6 +620,12 @@ typedef struct MessageCloneStack_ { StgTSO *tso; } MessageCloneStack; +typedef struct MessageUpdTSOFlag_ { + StgHeader header; + Message *link; + StgTSO *tso; + StgWord32 flag; +} MessageUpdTSOFlag; /* ---------------------------------------------------------------------------- Compact Regions ===================================== rts/include/stg/MiscClosures.h ===================================== @@ -152,6 +152,8 @@ RTS_ENTRY(stg_MSG_TRY_WAKEUP); RTS_ENTRY(stg_MSG_THROWTO); RTS_ENTRY(stg_MSG_BLACKHOLE); RTS_ENTRY(stg_MSG_CLONE_STACK); +RTS_ENTRY(stg_MSG_SET_TSO_FLAG); +RTS_ENTRY(stg_MSG_UNSET_TSO_FLAG); RTS_ENTRY(stg_MSG_NULL); RTS_ENTRY(stg_MVAR_TSO_QUEUE); RTS_ENTRY(stg_catch); ===================================== testsuite/tests/rts/T27131.hs ===================================== @@ -0,0 +1,81 @@ +{-# LANGUAGE MagicHash #-} +{-# LANGUAGE UnliftedFFITypes #-} + +module Main where + +import Control.Concurrent +import Control.Monad +import Foreign.C.Types +import GHC.Conc.Sync (ThreadId(..), forkOn, myThreadId, setNumCapabilities) +import GHC.Exts (ThreadId#) + +foreign import ccall unsafe "rts_enableStopNextBreakpoint" + rts_enableStopNextBreakpoint :: ThreadId# -> IO () + +foreign import ccall unsafe "rts_disableStopNextBreakpoint" + rts_disableStopNextBreakpoint :: ThreadId# -> IO () + +foreign import ccall unsafe "rts_enableStopAfterReturn" + rts_enableStopAfterReturn :: ThreadId# -> IO () + +foreign import ccall unsafe "rts_disableStopAfterReturn" + rts_disableStopAfterReturn :: ThreadId# -> IO () + +foreign import ccall unsafe "has_local_stop_next_breakpoint" + c_hasLocalStopNextBreakpoint :: IO CInt + +foreign import ccall unsafe "has_local_stop_after_return" + c_hasLocalStopAfterReturn :: IO CInt + +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 + +checkFlag + :: String + -> (ThreadId# -> IO ()) + -> (ThreadId# -> IO ()) + -> IO CInt + -> IO () +checkFlag label enable disable isMyThreadFlagSet = do + -- Print the main thread's capability (should be 0) + print =<< threadCapability =<< myThreadId + + -- Target thread will write its own flag value here + targetCheckVar <- newEmptyMVar + + -- Run the new TSO runs on capability 1 + ThreadId tid# <- forkOn 1 $ do + replicateM_ 2 $ do + replyVar <- takeMVar targetCheckVar + isSet <- (/= 0) <$> isMyThreadFlagSet + putMVar replyVar isSet + + -- Enable the other TSO's flag + enable tid# + -- It will check whether it is set and reply here + renderCheck label "set" =<< checkTarget targetCheckVar + + -- Ditto. + disable tid# + renderCheck label "unset" . not =<< checkTarget targetCheckVar + +checkTarget :: MVar (MVar Bool) -> IO Bool +checkTarget targetCheckVar = do + replyVar <- newEmptyMVar + putMVar targetCheckVar replyVar + takeMVar replyVar + +renderCheck :: String -> String -> Bool -> IO () +renderCheck label state ok = putStrLn $ + label ++ " " ++ state ++ ": " ++ if ok then "ok" else "failed" ===================================== testsuite/tests/rts/T27131.stdout ===================================== @@ -0,0 +1,6 @@ +(0,False) +TSO_STOP_NEXT_BREAKPOINT set: ok +TSO_STOP_NEXT_BREAKPOINT unset: ok +(0,False) +TSO_STOP_AFTER_RETURN set: ok +TSO_STOP_AFTER_RETURN unset: ok ===================================== testsuite/tests/rts/T27131_c.c ===================================== @@ -0,0 +1,15 @@ +#include "Rts.h" + +int has_local_stop_next_breakpoint(void) +{ + CapabilityPublic *cap = (CapabilityPublic *) rts_unsafeGetMyCapability(); + StgTSO *tso = cap->r.rCurrentTSO; + return (tso->flags & TSO_STOP_NEXT_BREAKPOINT) != 0; +} + +int has_local_stop_after_return(void) +{ + CapabilityPublic *cap = (CapabilityPublic *) rts_unsafeGetMyCapability(); + StgTSO *tso = cap->r.rCurrentTSO; + return (tso->flags & TSO_STOP_AFTER_RETURN) != 0; +} ===================================== testsuite/tests/rts/all.T ===================================== @@ -623,6 +623,12 @@ test('T20201b', [js_skip, exit_code(1)], compile_and_run, ['-with-rtsopts -A64z' test('T22012', [js_skip, extra_ways(['ghci'])], compile_and_run, ['T22012_c.c']) +test('T27131', + [ only_ways(['threaded1', 'threaded2']) + , req_ghc_with_threaded_rts + ], + compile_and_run, ['T27131_c.c']) + # Skip for JS platform as the JS RTS is always single threaded test('T22795a', [only_ways(['normal']), js_skip, req_ghc_with_threaded_rts], compile_and_run, ['-threaded']) test('T22795b', [only_ways(['normal']), js_skip], compile_and_run, ['-single-threaded']) View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/dbf1e2984c03433fe15c3416767dcf5... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/dbf1e2984c03433fe15c3416767dcf5... 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