#15417: Memory leaks because of too conservative isAlive check in the GC -------------------------------------+------------------------------------- Reporter: osa1 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Research needed Component: Runtime | Version: 8.5 System | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- (See also the mailing list [https://mail.haskell.org/pipermail/ghc- devs/2018-July/016027.html thread]) Static objects with no SRTs and pointer fields are currently ignored by `evacuate()`. This is efficient but causes trouble when checking alive- ness of static objects in `isAlive()`, which is used for (among other things) checking whether a weak's key has died. This causes leaks as value of a weak with static key will always be kept alive. Here's a demonstration: {{{#!haskell module Main where import System.Mem.Weak (mkWeak, deRefWeak) import System.Mem (performMajorGC) mkKey :: IO String mkKey = readFile "/dev/random" -- mkKey :: IO Int -- mkKey = return 1 main :: IO () main = do w <- mkKey >>= \k -> mkWeak k () Nothing performMajorGC performMajorGC performMajorGC deRefWeak w >>= print }}} The idea is that the first `mkKey` function returns a non-static string and this program prints `Nothing`. If I enable the second `mkKey` function the key is now a static object and the program prints `Just ()`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15417 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler