我可以确保 Haskell 执行原子 IO 吗? [英] Can I ensure that Haskell performs atomic IO?

问题描述

我在 haskell 中有两个线程来执行 IO.(他们只打印).类似于以下内容:

I have two threads in haskell that perform IO. (They print only). Something like the following:

thread1 :: IO ()
thread1 = putStrLn "One"

thread2 :: IO ()
thread2 = putStrLn "Two"

我目前得到的结果如下:

I am currently getting results like the following:

OnTwoe
OTnweo

如何确保每个线程都原子地完成其 IO?

How can I ensure that each thread completes its IO atomically?

推荐答案

使用同步变量来确保对资源的原子访问.一个简单的方法是使用 MVar:

Use a synchronization variable to ensure atomic access to the resource. A simple way is with an MVar:

main = do
   lock <- newMVar ()
   forkIO $ ... lock 
   forkIO $ ... lock

现在，为了不交错进行 IO，每个线程都获取锁:

Now, to do IO without interleaving, each thread takes the lock:

thread1 lock = do
      withMVar lock $ \_ -> putStrLn "foo"

thread2 lock = do
      withMVar lock $ \_ -> putStrLn "bar"

另一种设计是有一个专门的工作线程来执行所有putStrLns，然后您发送消息以通过 Chan 打印出来.

An alternate design is to have a dedicated worker thread that does all the putStrLns, and you send messages to print out over a Chan.

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