forkIO/killThread 与 forkProcess 的交互

Question

我写了下面的代码，注意到killThread块和线程仍在继续。只有当我在 forkProcess 中执行此操作时，才会发生这种情况，如果我删除 forkProcess，一切都会按预期工作。

法典

{-# LANGUAGE TupleSections #-}
module Main where
import Control.Concurrent
import Control.Monad
import System.Posix.Process
{-# NOINLINE primes #-}
primes :: [Integer]
primes = 2:[x | x <- [3..], all (not . flip isDivisorOf x) (takeWhile (< truncate (sqrt $ fromInteger x :: Double)) primes)]
  where x `isDivisorOf` y = y `rem` x == 0
evaluator :: Show a => [a] -> IO ()
evaluator xs = do
  putStrLn "[Evaluator] Started evaluator."
  forM_ xs $ x -> putStrLn $ "[Evaluator] Got result: " ++ show x
  putStrLn "[Evaluator] Evaluator exited."
test :: IO ThreadId
test = forkIO (evaluator $ filter ((== 13) . flip rem (79 * 5 * 7 * 3 * 3 * 2 * 3)) primes) -- Just some computation that doesn't finsish too fast
main :: IO ()
main = do
  pid <- forkProcess $ do
    a <- test
    threadDelay $ 4000 * 1000
    putStrLn "Canceling ..."
    killThread a
    putStrLn "Canceled"
  void $ getProcessStatus True False pid

输出

$ ghc test.hs -O -fforce-recomp -threaded -eventlog -rtsopts # I also tried with -threaded
$ ./test +RTS -N2  # I also tried without -N
[Evaluator] Started evaluator.
[Evaluator] Got result: 13
[Evaluator] Got result: 149323
[Evaluator] Got result: 447943
[Evaluator] Got result: 597253
[Evaluator] Got result: 746563
[Evaluator] Got result: 1045183
Canceling ...
[Evaluator] Got result: 1194493
[Evaluator] Got result: 1642423
[Evaluator] Got result: 1791733
[Evaluator] Got result: 2090353
[Evaluator] Got result: 2687593
[Evaluator] Got result: 3135523
[Evaluator] Got result: 3284833
[Evaluator] Got result: 4777933
[Evaluator] Got result: 5375173
^C[Evaluator] Got result: 5524483
^C

这不是

没有内存分配的常见问题，因此 GHC 的线程调度程序无法运行。我通过使用 +RTS -sstderr 运行程序来验证这一点，这表明垃圾收集器经常运行。我正在 linux 64 位上运行它。

Answer 1

此错误报告指出，尽管文档中没有说明异步异常，但forkProcess屏蔽了子进程中的异步异常。该行为应在 7.8.1 发布时修复。

当然，如果异步异常被屏蔽，killThread内部的throw将无限期地阻止。如果您只是删除main中包含 forkProcess 和 getProcessStatus 的行，程序将按预期工作：

module Main where
import           Control.Concurrent
import           Control.Monad
import           System.Posix.Process
{-# NOINLINE primes #-}
primes :: [Integer]
primes = 2:[ x | x <- [3..], all (not . flip isDivisorOf x) (takeWhile (< truncate (sqrt $ fromInteger x :: Double)) primes)]
  where x `isDivisorOf` y = y `rem` x == 0
evaluator :: Show a => [a] -> IO ()
evaluator = mapM_ $ x ->
  putStrLn $ "[Evaluator] Got result: " ++ show x
test :: IO ThreadId
test = forkIO (evaluator $ filter ((== 13) . flip rem (79 * 5 * 7 * 3 * 3 * 2 * 3)) primes) -- Just some computation that doesn't finsish too fast
main :: IO ()
main = do
  a <- test
  threadDelay $ 4000 * 1000
  putStrLn "Canceling ..."
  killThread a
  putStrLn "Canceled"

我用ghc --make -threaded async.hs构建它，用./async +RTS -N4运行。

如果由于某种原因需要单独的进程，则必须在 GHC 7.6.3 中的子进程中手动取消屏蔽异步异常。