8

文档getErrno内容如下:

获取当前线程中errno的当前值。

我不清楚这是否意味着当前的操作系统线程。特别是,errno当 Haskell 线程从一个 OS 线程迁移到另一个时,(线程)运行时是否会获取并隐藏?

这个问题似乎是相关的,但我不清楚那里所说的是否与操作系统或 Haskell 线程有关。

4

1 回答 1

7

至少对于最新版本的 GHC,运行时保存errno在线程存储对象 ( TSO) 中,并在将运行时线程迁移到另一个 OS 线程时负责管理它。errno这意味着在 unbound ( forkIO) 和 bound ( forkOS) 线程中依赖应该是安全的。这是针对 Linux 的测试:

err.hs

import Control.Concurrent
import Control.Exception
import Foreign.C

foreign import ccall safe get_ostid :: IO CUInt
foreign import ccall safe sleep :: CUInt -> IO CUInt
foreign import ccall unsafe get_errno :: IO CInt
foreign import ccall unsafe set_errno :: CInt -> IO ()

forkIO' f = do
  done <- newEmptyMVar
  forkIO (f `finally` putMVar done ())
  return (takeMVar done)

prefix = do
  id <- get_ostid
  return $ show id ++ ": "

main = do
  wait <- forkIO' $ do -- spawn a lightweight thread
    errno <- get_errno
    (putStr =<< prefix) >> putStrLn ("outer errno is " ++ show errno)
    (putStr =<< prefix) >> putStrLn "Setting outer errno to 3"
    set_errno 3
    wait' <- forkIO' $ do -- spawn another lightweight thread
      errno <- get_errno
      (putStr =<< prefix) >> putStrLn ("inner errno is " ++ show errno)
      (putStr =<< prefix) >> putStrLn "Setting inner errno to 2"
      set_errno 2
      sleep 2 -- force this lightweight thread to tie up the OS thread
      errno <- get_errno
      (putStr =<< prefix) >> putStrLn ("inner errno is " ++ show errno)
    threadDelay 1000000 -- wait a second
    -- By now, we should be in another OS thread.
    errno <- get_errno
    (putStr =<< prefix) >> putStrLn ("outer errno is " ++ show errno)
    wait'
  wait

err.c

#include <errno.h>
#include <sys/syscall.h>
#include <unistd.h>

int get_errno(void) { return errno; }
void set_errno(int e) { errno = e; }

unsigned get_ostid(void) {
  return syscall(SYS_gettid);
}

编译:

ghc -o err -threaded err.hs err.c

结果应该类似于:

12282: outer errno is 0
12282: Setting outer errno to 3
12282: inner errno is 0
12282: Setting inner errno to 2
12283: outer errno is 3
12282: inner errno is 2

操作系统线程 ID 打印在每行的开头。请注意,errno3迁移到第二个 OS 线程 ( 12283)。

于 2013-01-27T23:22:45.070 回答