#9765: Strange behavior of GC under ghci -------------------------------------+------------------------------------- Reporter: remdezx | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: GHCi | Version: 7.8.3 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Incorrect Blocked By: | result at runtime Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Releasing the result of `newForeignPtr nullFunPtr nullPtr` end in core dump, due to the fact that finalizer function is set to null pointer. When I run something like this in GHCI: {{{#!hs

import System.Mem import Foreign.Ptr import Foreign.ForeignPtr import System.IO.Unsafe import qualified Data.Map as Map a <- return $ Map.singleton 1 (unsafePerformIO $ newForeignPtr nullFunPtr nullPtr) Loading package array-0.5.0.0 ... linking ... done. Loading package deepseq-1.3.0.2 ... linking ... done. Loading package containers-0.5.5.1 ... linking ... done. print a fromList [(1,0x0000000000000000)] performGC ^D Leaving GHCi. [1] 3782 segmentation fault (core dumped) ghci }}}

it wont crash until exit from ghci which is correct. But if I do something similar but using `let` binding it will crash even if variable `a` didn't lose its scope {{{#!hs

import System.Mem import Foreign.Ptr import Foreign.ForeignPtr import System.IO.Unsafe import qualified Data.Map as Map let a = Map.singleton 1 (unsafePerformIO $ newForeignPtr nullFunPtr nullPtr) Loading package array-0.5.0.0 ... linking ... done. Loading package deepseq-1.3.0.2 ... linking ... done. Loading package containers-0.5.5.1 ... linking ... done. print a fromList [(1,0x0000000000000000)] [1] 3842 segmentation fault (core dumped) ghci }}}

Why is there a difference between doing it with `do` notation and with `let` binding? I also expected that if I rebind variable `a` it will lose it's scope and will be released but it is not (see below) {{{#!hs

import System.Mem import Foreign.Ptr import Foreign.ForeignPtr import System.IO.Unsafe import qualified Data.Map as Map a <- return $ Map.singleton 1 (unsafePerformIO $ newForeignPtr nullFunPtr nullPtr) Loading package array-0.5.0.0 ... linking ... done. Loading package deepseq-1.3.0.2 ... linking ... done. Loading package containers-0.5.5.1 ... linking ... done. print a fromList [(1,0x0000000000000000)] a <- return () -- rebinding varable a, it is no longer used performGC -- no crash, varaible a not released }}}

-- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9765 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler