Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC Commits: 5b5d9d47 by Ben Gamari at 2025-08-25T14:29:35-04:00 Revert "STM: don't create a transaction in the rhs of catchRetry# (#26028)" This reverts commit 0a5836891ca29836a24c306d2a364c2e4b5377fd - - - - - 6 changed files: - rts/PrimOps.cmm - rts/RaiseAsync.c - rts/STM.c - − testsuite/tests/lib/stm/T26028.hs - − testsuite/tests/lib/stm/T26028.stdout - − testsuite/tests/lib/stm/all.T Changes: ===================================== rts/PrimOps.cmm ===================================== @@ -1211,27 +1211,16 @@ INFO_TABLE_RET(stg_catch_retry_frame, CATCH_RETRY_FRAME, gcptr trec, outer, arg; trec = StgTSO_trec(CurrentTSO); - if (running_alt_code != 1) { - // When exiting the lhs code of catchRetry# lhs rhs, we need to cleanup - // the nested transaction. - // See Note [catchRetry# implementation] - outer = StgTRecHeader_enclosing_trec(trec); - (r) = ccall stmCommitNestedTransaction(MyCapability() "ptr", trec "ptr"); - if (r != 0) { - // Succeeded in first branch - StgTSO_trec(CurrentTSO) = outer; - return (ret); - } else { - // Did not commit: abort and restart. - StgTSO_trec(CurrentTSO) = outer; - jump stg_abort(); - } - } - else { - // nothing to do in the rhs code of catchRetry# lhs rhs, it's already - // using the parent transaction (not a nested one). - // See Note [catchRetry# implementation] - return (ret); + outer = StgTRecHeader_enclosing_trec(trec); + (r) = ccall stmCommitNestedTransaction(MyCapability() "ptr", trec "ptr"); + if (r != 0) { + // Succeeded (either first branch or second branch) + StgTSO_trec(CurrentTSO) = outer; + return (ret); + } else { + // Did not commit: abort and restart. + StgTSO_trec(CurrentTSO) = outer; + jump stg_abort(); } } @@ -1464,26 +1453,21 @@ retry_pop_stack: outer = StgTRecHeader_enclosing_trec(trec); if (frame_type == CATCH_RETRY_FRAME) { - // The retry reaches a CATCH_RETRY_FRAME before the ATOMICALLY_FRAME - + // The retry reaches a CATCH_RETRY_FRAME before the atomic frame + ASSERT(outer != NO_TREC); + // Abort the transaction attempting the current branch + ccall stmAbortTransaction(MyCapability() "ptr", trec "ptr"); + ccall stmFreeAbortedTRec(MyCapability() "ptr", trec "ptr"); if (!StgCatchRetryFrame_running_alt_code(frame) != 0) { - // Retrying in the lhs of catchRetry# lhs rhs, i.e. in a nested - // transaction. See Note [catchRetry# implementation] - - // check that we have a parent transaction - ASSERT(outer != NO_TREC); - - // Abort the nested transaction - ccall stmAbortTransaction(MyCapability() "ptr", trec "ptr"); - ccall stmFreeAbortedTRec(MyCapability() "ptr", trec "ptr"); - - // As we are retrying in the lhs code, we must now try the rhs code - StgTSO_trec(CurrentTSO) = outer; + // Retry in the first branch: try the alternative + ("ptr" trec) = ccall stmStartTransaction(MyCapability() "ptr", outer "ptr"); + StgTSO_trec(CurrentTSO) = trec; StgCatchRetryFrame_running_alt_code(frame) = 1 :: CInt; // true; R1 = StgCatchRetryFrame_alt_code(frame); jump stg_ap_v_fast [R1]; } else { - // Retry in the rhs code: propagate the retry + // Retry in the alternative code: propagate the retry + StgTSO_trec(CurrentTSO) = outer; Sp = Sp + SIZEOF_StgCatchRetryFrame; goto retry_pop_stack; } ===================================== rts/RaiseAsync.c ===================================== @@ -1043,7 +1043,8 @@ raiseAsync(Capability *cap, StgTSO *tso, StgClosure *exception, } case CATCH_STM_FRAME: - // CATCH_STM frame within an atomically block: abort the + case CATCH_RETRY_FRAME: + // CATCH frames within an atomically block: abort the // inner transaction and continue. Eventually we will // hit the outer transaction that will get frozen (see // above). @@ -1055,40 +1056,14 @@ raiseAsync(Capability *cap, StgTSO *tso, StgClosure *exception, { StgTRecHeader *trec = tso -> trec; StgTRecHeader *outer = trec -> enclosing_trec; - debugTraceCap(DEBUG_stm, cap, "raiseAsync: traversing CATCH_STM frame"); + debugTraceCap(DEBUG_stm, cap, + "found atomically block delivering async exception"); stmAbortTransaction(cap, trec); stmFreeAbortedTRec(cap, trec); tso -> trec = outer; break; }; - case CATCH_RETRY_FRAME: - // CATCH_RETY frame within an atomically block: if we're executing - // the lhs code, abort the inner transaction and continue; if we're - // executing thr rhs, continue (no nested transaction to abort. See - // Note [catchRetry# implementation]). Eventually we will hit the - // outer transaction that will get frozen (see above). - // - // As for the CATCH_STM_FRAME case above, we do not care - // whether the transaction is valid or not because its - // possible validity cannot have caused the exception - // and will not be visible after the abort. - { - if (!((StgCatchRetryFrame *)frame) -> running_alt_code) { - debugTraceCap(DEBUG_stm, cap, "raiseAsync: traversing CATCH_RETRY frame (lhs)"); - StgTRecHeader *trec = tso -> trec; - StgTRecHeader *outer = trec -> enclosing_trec; - stmAbortTransaction(cap, trec); - stmFreeAbortedTRec(cap, trec); - tso -> trec = outer; - } - else - { - debugTraceCap(DEBUG_stm, cap, "raiseAsync: traversing CATCH_RETRY frame (rhs)"); - } - break; - }; - default: // see Note [Update async masking state on unwind] in Schedule.c if (*frame == (W_)&stg_unmaskAsyncExceptionszh_ret_info) { ===================================== rts/STM.c ===================================== @@ -1505,30 +1505,3 @@ void stmWriteTVar(Capability *cap, } /*......................................................................*/ - - - -/* - -Note [catchRetry# implementation] -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -catchRetry# creates a nested transaction for its lhs: -- if the lhs transaction succeeds: - - the lhs transaction is committed - - its read-variables are merged with those of the parent transaction - - the rhs code is ignored -- if the lhs transaction retries: - - the lhs transaction is aborted - - its read-variables are merged with those of the parent transaction - - the rhs code is executed directly in the parent transaction (see #26028). - -So note that: -- lhs code uses a nested transaction -- rhs code doesn't use a nested transaction - -We have to take which case we're in into account (using the running_alt_code -field of the catchRetry frame) in catchRetry's entry code, in retry# -implementation, and also when an async exception is received (to cleanup the -right number of transactions). - -*/ ===================================== testsuite/tests/lib/stm/T26028.hs deleted ===================================== @@ -1,23 +0,0 @@ -module Main where - -import GHC.Conc - -forever :: IO String -forever = delay 10 >> forever - -terminates :: IO String -terminates = delay 1 >> pure "terminates" - -delay s = threadDelay (1000000 * s) - -async :: IO a -> IO (STM a) -async a = do - var <- atomically (newTVar Nothing) - forkIO (a >>= atomically . writeTVar var . Just) - pure (readTVar var >>= maybe retry pure) - -main :: IO () -main = do - x <- mapM async $ terminates : replicate 50000 forever - r <- atomically (foldr1 orElse x) - print r ===================================== testsuite/tests/lib/stm/T26028.stdout deleted ===================================== @@ -1 +0,0 @@ -"terminates" ===================================== testsuite/tests/lib/stm/all.T deleted ===================================== @@ -1 +0,0 @@ -test('T26028', only_ways(['threaded1']), compile_and_run, ['-O2']) View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/5b5d9d474631f14380cf05acb9c66af6... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/5b5d9d474631f14380cf05acb9c66af6... You're receiving this email because of your account on gitlab.haskell.org.