http://hackage.haskell.org/package/SafeSemaphore My intent is for this to supersede the implementation of semaphore in Control.Concurrent.QSem and Control.Concurrent.QSemN currently in the
http://haskell.org/haskellwiki/SafeConcurrent shows the included TestKillSem.hs file and its output. This shows how
There is a leak in base. A leak in the semaphores. Drip, drip, drip. I would like to announce a new package SafeSemaphore, at base package. This is needed because there is a quantity loss bug in QSem and QSemN. Any thread blocked while waiting might be killed. In this case a later signal will pass quantity to the dead thread. This quantity is never received and is thus lost to the program. This is logged in GHC's bug tracker at http://hackage.haskell.org/trac/ghc/ticket/3160 The MSem and MSemN modules in SafeSemaphore fix this problem and are extended replacement for QSem/QSemN with what I think is an improved and extended API. Under the hood a MSem/MSemN only ever allocates three MVars, instead of one MVar for every blocking waiter that QSem/QSemN allocate. The related Haskell wiki page at the QSem/QSemN bug can be triggered and shows that MSem/MSemN is immune to this leak. Cheers, Chris Kuklewicz