Ruby暂停线程

Question

在ruby中，是否可能导致线程从另一个并发运行的线程暂停。

下面是我到目前为止编写的代码。我希望用户能够输入'pause thread'和sample500线程来暂停。

#!/usr/bin/env ruby

# Creates a new thread executes the block every intervalSec for durationSec.
def DoEvery(thread, intervalSec, durationSec)
    thread = Thread.new do
        start = Time.now

        timeTakenToComplete = 0
        loopCounter = 0
        while(timeTakenToComplete < durationSec && loopCounter += 1)

            yield

            finish = Time.now

            timeTakenToComplete = finish - start

            sleep(intervalSec*loopCounter - timeTakenToComplete)    
        end
    end
end

# User input loop.
exit = nil
while(!exit)
    userInput = gets
    case userInput
    when "start thread\n"
        sample500 = Thread
        beginTime = Time.now
        DoEvery(sample500, 0.5, 30) {File.open('abc', 'a') {|file| file.write("a\n")}}
    when "pause thread\n"
        sample500.stop
    when "resume thread"
        sample500.run
    when "exit\n"
        exit = TRUE
    end
end

Answer 1

将Thread对象作为参数传递给DoEvery函数是没有意义的，因为你立即用Thread.new覆盖它，看看这个修改过的版本：

def DoEvery(intervalSec, durationSec)
    thread = Thread.new do
        start = Time.now
        Thread.current["stop"] = false

        timeTakenToComplete = 0
        loopCounter = 0
        while(timeTakenToComplete < durationSec && loopCounter += 1)
            if Thread.current["stop"]
              Thread.current["stop"] = false
              puts "paused"
              Thread.stop
            end

            yield

            finish = Time.now

            timeTakenToComplete = finish - start

            sleep(intervalSec*loopCounter - timeTakenToComplete)

        end
    end
    thread
end

# User input loop.
exit = nil
while(!exit)
    userInput = gets
    case userInput
    when "start thread\n"
        sample500 = DoEvery(0.5, 30) {File.open('abc', 'a') {|file| file.write("a\n")} }
    when "pause thread\n"
        sample500["stop"] = true
    when "resume thread\n"
        sample500.run
    when "exit\n"
        exit = TRUE
    end
end

这里DoEvery返回新的线程对象。另请注意，Thread.stop在运行线程内部调用，不能直接阻止另一个线程，因为它不安全。

Answer 2

您可能能够更好地完成使用Ruby Fiber对象的尝试，并且可能在运行的系统上实现更高的效率。

Fibers是在Ruby中实现轻量级协同并发的原语。基本上它们是创建可以暂停和恢复的代码块的一种方法，就像线程一样。主要区别在于它们永远不会被抢占，并且调度必须由程序员而不是VM完成。

记住MRI的当前实现Ruby不提供任何并发运行的线程，你能够完成的最好的是green threaded程序，以下是一个很好的例子：

require "fiber"

f1 = Fiber.new { |f2| f2.resume Fiber.current; while true; puts "A"; f2.transfer; end }
f2 = Fiber.new { |f1| f1.transfer; while true; puts "B"; f1.transfer; end }

f1.resume f2 # =>
  # A
  # B 
  # A
  # B
  # .
  # .
  # .