Haskell语言学习笔记（84）Concurrent

Control.Concurrent

Prelude> import Control.Concurrent
Prelude Control.Concurrent> 

Control.Concurrent 模块属于标准库，不需要安装。

forkIO threadDelay

• data ThreadId
  代表线程句柄的类型。
• forkIO :: IO () -> IO ThreadId
  创建线程返回线程句柄，在新的线程中运行所给的IO计算参数。
• threadDelay :: Int -> IO ()
  当前线程挂起 n 微秒（百万分之一秒，10负6次方分之一秒）。

示例

haskell-simple-concurrency

module Threads where

import Control.Concurrent (forkIO, threadDelay)
import Data.Foldable (for_)

main = do
    -- Synchronously perform some work.
    printMessagesFrom "main"

    -- Fork a new thread to do some work in the background.
    forkIO (printMessagesFrom "fork")

    -- Fork another thread using an inline function!
    forkIO (do
        putStrLn "starting!"
        sleepMs 5
        putStrLn "ending!")

    -- Wait for threads to finish.
    sleepMs 10

-- A simple function that prints three messages with a little delay between them.
printMessagesFrom name = for_ [1..3] printMessage
    where printMessage i = do
            sleepMs 1
            putStrLn (name ++ " number " ++ show i)

-- A utility function - threadDelay takes microseconds, which is slightly annoying.
sleepMs n = threadDelay (n * 1000)

*Threads> main
main number 1
main number 2
main number 3
starting!
fork number 1
fork number 2
fork number 3
ending!

• forkIO (printMessagesFrom "fork")
  forkIO (do putStrLn "starting!"; sleepMs 5; putStrLn "ending!")
  这里使用 forkIO 先后启动了两个线程：打印数字的线程和打印开始结束的线程
  打印开始结束的过程为：打印开始，然后等待 5 毫秒，最后打印结束。
• printMessagesFrom name = for_ [1..3] printMessage
  打印数字函数一共打印三个数字
• printMessage i = do ( sleepMs 1; putStrLn (name ++ " number " ++ show i))
  每次打印数字之前先等待 1 毫秒
• 所以最后结果为

starting!          -- 0 millisecond
fork number 1      -- 1 millisecond
fork number 2      -- 2 milliseconds
fork number 3      -- 3 milliseconds
ending!            -- 5 milliseconds

Haskell语言学习笔记（84）Concurrent

原文：https://www.cnblogs.com/zwvista/p/9339587.html