ForkIO/killThread与forkProcess的交互

Question

我已经写了下面的代码，并注意到 killThread 块和线程仍在继续。只有当我在forkProcess中执行此操作时，如果我删除forkProcess，则一切都按预期工作。

密码

{-# 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

这不是通常的问题，没有内存分配，因此GHC的线程调度程序不运行。我通过运行程序验证了这一点 +RTS -sstderr, ，这表明垃圾收集器运行非常频繁。我在linux64位上运行这个。

Answer 1

这 错误报告 注意到 forkProcess 屏蔽子进程中的异步异常，尽管文档中没有这样的指示。该行为应在发布时在7.8.1中修复。

当然，如果异步异常被屏蔽，则 throw 在 killThread 将无限期阻止。如果你只是删除了 main 包含 forkProcess 和 getProcessStatus, ，该程序按预期工作:

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"

我用它来建造 ghc --make -threaded async.hs 和运行 ./async +RTS -N4.

如果由于某种原因需要单独的进程，则必须在GHC7.6.3中的子进程中手动取消屏蔽异步异常。