#7930: Nested STM Invariants are lost ---------------------------------+------------------------------------------ Reporter: fryguybob | Owner: fryguybob Type: bug | Status: new Priority: normal | Milestone: Component: Runtime System | Version: 7.6.3 Keywords: STM | Os: Unknown/Multiple Architecture: Unknown/Multiple | Failure: Incorrect result at runtime Difficulty: Unknown | Testcase: Blockedby: | Blocking: Related: | ---------------------------------+------------------------------------------ Comment(by timharris): Hi -- here are some comments I sent Simon earlier. I do not usually use Trac, but feel free to contact me on e-mail, tim.harris@gmail.com --Tim The initial comment re invariants_to_check sounds correct. I think we added nested transactions after adding invariants. I don't remember thinking about the interaction before, but retaining the invariants from within a nested transactions sounds correct (since, in the absence of exceptions in X, I would expect catch X Y to behave like X). The other cases are more complex. I don't think the descriptions I wrote for the functions are very clear. e.g., for alwaysSucceeds, exactly what it means for an invariant to be true (Returns true? Does not throw? Does not retry? What if it loops?) I think the bug report's authors understand all these problems. I'd probably go back to the semantics in Fig 4 of http://timharris.co.uk/papers/2006-transact.pdf and write the functions descriptions again based on that, and then fix up the code as necessary. "check X" in the semantics is intended to be "always X" in the code. "check X" will throw if X throws, and retry if X retries. It tests X in this way immediately, and then again on the commit of each transaction (including the current one). I don't think the current code implements this correctly. With "always X" fixed, I'd then define "alwaysSucceeds X" in terms of "always" rather than vice-versa. (I think it should just be always ( X >> return true).) -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7930#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler