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Summary

System.IO.readFile leaks file descriptors in the presence of asynchronous exceptions.

Steps to reproduce

Run

module Main where

import Control.Concurrent
import Data.Foldable
import System.IO

main :: IO ()
main =
  do
    for_ [1..300] go
    -- at this point, execute `ls -l "/proc/$(pidof readfile-test-exe)/fd"`
    -- every listing of `test.txt` constitutes a leaked file descriptor
    getLine
    pure ()

go :: Integer -> IO ()
go n =
  do
    id <- forkIO (readFile "test.txt" >>= putStr)
    threadDelay 1
    killThread id
    pure ()

(https://gitlab.com/rdnz/readfile-test/-/blob/system-io/app/Main.hs).

Execute ls -l "/proc/$(pidof readfile-test-exe)/fd" in a new terminal.

Expected behavior

ls -l "/proc/$(pidof readfile-test-exe)/fd" should not list any test.txt.

Environment

• GHC version used: 8.8.4
• Operating System: NixOS 20.03.2843.14006b724f3
• Kernel Version: 5.4.60
• OS Type: 64-bit
• Processors: 2 × Intel® Core™2 Duo CPU P8700 @ 2.53GHz
• Memory: 3.6 GiB of RAM