Re: [GHC] #3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar
#3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar --+- Reporter: ChrisKuklewicz | Owner: simonmar Type: bug | Status: closed Priority: normal | Milestone: 7.6.1 Component: libraries/base |Version: 7.0.2 Resolution: wontfix | Keywords: Os: Unknown/Multiple | Architecture: Unknown/Multiple Failure: Incorrect result at runtime | Difficulty: Unknown Testcase: | Blockedby: Blocking: |Related: --+- Changes (by simonmar): * status: new = closed * resolution: = wontfix Comment: The versions in base have been deprecated in 7.6.1, and we now recommend that people use the `SafeSemaphore` package instead. This leaves the way open for having a `concurrent` package in the future that would combine a number of useful concurrent data structures with things like `async`. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3160#comment:21 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar
#3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar --+- Reporter: ChrisKuklewicz | Owner: simonmar Type: bug | Status: new Priority: normal | Milestone: 7.6.1 Component: libraries/base |Version: 7.0.2 Resolution: | Keywords: Os: Unknown/Multiple | Architecture: Unknown/Multiple Failure: Incorrect result at runtime | Difficulty: Unknown Testcase: | Blockedby: Blocking: |Related: --+- Changes (by simonmar): * owner: = simonmar Comment: Thanks. At the very least we should import the STM versions for 7.6.1. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3160#comment:20 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar
#3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar --+- Reporter: ChrisKuklewicz | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.6.1 Component: libraries/base |Version: 7.0.2 Resolution: | Keywords: Os: Unknown/Multiple | Architecture: Unknown/Multiple Failure: Incorrect result at runtime | Difficulty: Unknown Testcase: | Blockedby: Blocking: |Related: --+- Comment(by ChrisKuklewicz): I have updated SafeSemaphore to 0.9.0 on hackage and git, http://github.com/ChrisKuklewicz/SafeSemaphore I have done several different things with this release: There is a new Control.Concurrent.SSem module based on STM that is dead simple and replaces QSem and QSemN. I have not made a SampleVar replacement with STM yet. The raw STM version is in Control.Concurrent.STM.SSem. This does guarantee FIFO operation and so has different starvation possibilities, especially with big and small requests to waitN. The MSem.hs file is now a literate MSem.lhs file. This has much more elaborate comments discussing how the invariants are maintained. The uninteruptableMask_ is only being used for the quick signal operation to ensure bracket works properly. The MSemN.hs file is now a literate MSemN.lhs file. This has extensively documented invariants and short proof arguments that they are maintained. The uninteruptableMask_ is used both in signal and to recover from interrupted wait operators. The new MSemN2.hs file is a variant of MSemN.lhs that does NOT use uninteruptableMask_ in the wait operation at all. Instead it makes every wait call check for the possible interruption of the previous wait. The uninteruptableMask_ is not used on every signal call, but is used in the with combinator to guard its call to signal. For replacing QSem/QSemN/SampleVar I will update the patch with the consensus design. I have announced this 0.9.0 release to the Haskell-Cafe mailing list and included a link to this ticket. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3160#comment:19 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar
#3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar --+- Reporter: ChrisKuklewicz | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.6.1 Component: libraries/base |Version: 7.0.2 Resolution: | Keywords: Os: Unknown/Multiple | Architecture: Unknown/Multiple Failure: Incorrect result at runtime | Difficulty: Unknown Testcase: | Blockedby: Blocking: |Related: --+- Changes (by liyang): * cc: hackage.haskell.org@… (added) -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3160#comment:18 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar
#3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar --+- Reporter: ChrisKuklewicz | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.6.1 Component: libraries/base |Version: 7.0.2 Resolution: | Keywords: Os: Unknown/Multiple | Architecture: Unknown/Multiple Failure: Incorrect result at runtime | Difficulty: Unknown Testcase: | Blockedby: Blocking: |Related: --+- Changes (by simonpj): * owner: simonmar = * status: patch = new -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3160#comment:17 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar
#3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar -+-- Reporter: ChrisKuklewicz| Owner: simonmar Type: bug | Status: patch Priority: normal| Milestone: 7.6.1 Component: libraries/base| Version: 7.0.2 Keywords:| Os: Unknown/Multiple Architecture: Unknown/Multiple | Failure: Incorrect result at runtime Difficulty: Unknown |Testcase: Blockedby:|Blocking: Related:| -+-- Comment(by ChrisKuklewicz): Ok, I see the difficulty. There are now two things I should do. One is that I should create a STM-based semaphore implementation. The second is that I should make a much clearer version of the MVar based code. As for the current code, it would be a good thing to add a note to the documentation that the semaphore invariants can be broken when threads are killed. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3160#comment:16 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar
#3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar -+-- Reporter: ChrisKuklewicz| Owner: simonmar Type: bug | Status: patch Priority: normal| Milestone: 7.6.1 Component: libraries/base| Version: 7.0.2 Keywords:| Os: Unknown/Multiple Architecture: Unknown/Multiple | Failure: Incorrect result at runtime Difficulty: Unknown |Testcase: Blockedby:|Blocking: Related:| -+-- Comment(by simonmar): The problem is that I just don't understand the patches. You sent a long and detailed explanation for which I'm very grateful, but nevertheless it would take a long time for me to understand your algorithms, and I'm not confident that I would be able to spot any bugs if there are any. Furthermore, you have used `uninterruptibleMask` in at least one place, which makes me very uneasy. On the other hand, we know the current code is broken. I'd be much more comfortable with using STM here. The code would be obviously correct, and probably only slightly slower than an optimised MVar implementation (and maybe even faster - all those `mask`s and `catch`es are not cheap). -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3160#comment:15 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar
#3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar -+-- Reporter: ChrisKuklewicz| Owner: simonmar Type: bug | Status: patch Priority: normal| Milestone: 7.6.1 Component: libraries/base| Version: 7.0.2 Keywords:| Os: Unknown/Multiple Architecture: Unknown/Multiple | Failure: Incorrect result at runtime Difficulty: Unknown |Testcase: Blockedby:|Blocking: Related:| -+-- Comment(by ChrisKuklewicz): A small proposition: If someone would merge it into GHC then I will update the patch to merge cleanly with the desired trunk. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3160#comment:14 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar
#3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar -+-- Reporter: ChrisKuklewicz|Owner: simonmar Type: bug | Status: patch Priority: normal|Milestone: 7.4.1 Component: libraries/base| Version: 7.0.2 Keywords:| Testcase: Blockedby:| Difficulty: Unknown Os: Unknown/Multiple | Blocking: Architecture: Unknown/Multiple | Failure: Incorrect result at runtime -+-- Changes (by igloo): * milestone: 7.2.1 = 7.4.1 -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3160#comment:12 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar
#3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar -+-- Reporter: ChrisKuklewicz|Owner: simonmar Type: bug | Status: patch Priority: normal|Milestone: 7.2.1 Component: libraries/base| Version: 7.0.2 Keywords:| Testcase: Blockedby:| Difficulty: Unknown Os: Unknown/Multiple | Blocking: Architecture: Unknown/Multiple | Failure: Incorrect result at runtime -+-- Changes (by igloo): * owner: = simonmar Comment: Patches are in here: http://www.haskell.org/pipermail/cvs- ghc/2011-April/061461.html Simon said in that thread he'd take a look, so making him owner. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3160#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar
#3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar -+-- Reporter: ChrisKuklewicz|Owner: Type: bug | Status: patch Priority: normal|Milestone: 7.2.1 Component: libraries/base| Version: 7.0.2 Keywords:| Testcase: Blockedby:| Difficulty: Unknown Os: Unknown/Multiple | Blocking: Architecture: Unknown/Multiple | Failure: Incorrect result at runtime -+-- Changes (by ChrisKuklewicz): * status: new = patch Comment: I have submitted a set of 6 patches to cvs-ghc mailing list. The first 3 are for the testsuite and the second 3 are against base. All against a recent git pull. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3160#comment:10 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar
#3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar -+-- Reporter: ChrisKuklewicz|Owner: Type: bug | Status: new Priority: normal|Milestone: 7.2.1 Component: libraries/base| Version: 7.0.2 Keywords:| Testcase: Blockedby:| Difficulty: Unknown Os: Unknown/Multiple | Blocking: Architecture: Unknown/Multiple | Failure: Incorrect result at runtime -+-- Changes (by ChrisKuklewicz): * failure: None/Unknown = Incorrect result at runtime Comment: I have updated SafeSemaphore to version 0.5.0 which includes a new MSampleVar module. This fixes the problem in SampleVar where any thread that dies while waiting to read the SampleVar leaves the SampleVar in a broken state. In this broken state a future writeSampleVar can block indefinitely trying to replace the current value. The TestKillSem.hs in SafeSemaphore has been updated to also demonstrate that MSampleVar fixes this bug in SampleVar. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3160#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar
#3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar -+-- Reporter: ChrisKuklewicz|Owner: Type: bug | Status: new Priority: normal|Milestone: 7.2.1 Component: libraries/base| Version: 7.0.2 Keywords:| Testcase: Blockedby:| Difficulty: Unknown Os: Unknown/Multiple | Blocking: Architecture: Unknown/Multiple | Failure: None/Unknown -+-- Changes (by ChrisKuklewicz): * cc: ChrisKuklewicz (added) * version: 6.10.2 = 7.0.2 Comment: I have uploaded [http://hackage.haskell.org/package/SafeSemaphore SafeSemaphore] to hackage. The MSem and MSemQ there can supersede QSem and QSemN. The included TestKillSem.hs demonstrates the error in QSem QSemN and the fix in MSem MSemN. You can browse TestKillSem and its results online at the [http://haskell.org/haskellwiki/SafeConcurrent#TestKillSem haskell wiki page]. The API for QSem is improved in MSem to handle negative numbers and is based on Integer instead of Int. The API for QSemN is greatly expanded in MSemN. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3160#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar
#3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar -+-- Reporter: ChrisKuklewicz | Owner: Type: bug | Status: new Priority: normal | Milestone: 6.14.1 Component: libraries/base |Version: 6.10.2 Resolution: | Keywords: Difficulty: Unknown | Os: Unknown/Multiple Testcase: | Architecture: Unknown/Multiple Failure: None/Unknown| -+-- Changes (by igloo): * failure: = None/Unknown * milestone: 6.12.1 = 6.14.1 Comment: The simplest way forward might be to remove them from base, and put them in a de-coupled concurrency package. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3160#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar
#3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar -+-- Reporter: ChrisKuklewicz|Owner: Type: bug | Status: new Priority: normal|Milestone: 6.12.1 Component: libraries/base| Version: 6.10.2 Severity: major | Resolution: Keywords:| Difficulty: Unknown Testcase:| Os: Unknown/Multiple Architecture: Unknown/Multiple | -+-- Changes (by igloo): * milestone: = 6.12.1 -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3160#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar
#3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar -+-- Reporter: ChrisKuklewicz|Owner: Type: bug | Status: new Priority: normal|Milestone: Component: libraries/base| Version: 6.10.2 Severity: major | Resolution: Keywords:| Difficulty: Unknown Testcase:| Os: Unknown/Multiple Architecture: Unknown/Multiple | -+-- Comment (by simonmar): I think rather than trying to get things right with `modifyMVar` and `withMVar`, we should try using STM for these abstractions. I suspect that the overhead of `modifyMVar` and co is comparable to the overhead of using STM (we measured this result for Chan in the original Haskell STM paper), and the STM version is much easier to get right. It would let us supply composable versions of the operations, too. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3160#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar
#3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar -+-- Reporter: ChrisKuklewicz|Owner: Type: bug | Status: new Priority: normal|Milestone: Component: libraries/base| Version: 6.10.2 Severity: major | Resolution: Keywords:| Difficulty: Unknown Testcase:| Os: Unknown/Multiple Architecture: Unknown/Multiple | -+-- Changes (by igloo): * difficulty: = Unknown Comment: See also http://haskell.org/haskellwiki/SafeConcurrent -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3160#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar
#3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar --+- Reporter: ChrisKuklewicz| Owner: Type: bug | Status: new Priority: normal| Milestone: Component: libraries/base|Version: 6.10.2 Severity: major | Resolution: Keywords:| Testcase: Os: Unknown/Multiple | Architecture: Unknown/Multiple --+- Changes (by greenrd): * cc: gree...@greenrd.org (added) -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3160#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
[GHC] #3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar
#3160: No exception safety in Control.Concurrent.QSem QSemN and SampleVar -+-- Reporter: ChrisKuklewicz| Owner: Type: bug | Status: new Priority: normal| Component: libraries/base Version: 6.10.2| Severity: major Keywords:| Testcase: Os: Unknown/Multiple | Architecture: Unknown/Multiple -+-- Looking at the code for QSem, QSemN, and SampleVar shows they all use a takeMVar then putMVar programming idiom. None of these are exception safe. An unlucky killThread will leave the MVar empty and cause the rest of the program to malfunction. The solution is to rewrite them using withMVar and modifyMVar(_) to prevent the MVar from being left empty in the event of an exception. Note: QSem also needs the bugfix in #3159 -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3160 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
