forkmanager fork() function is unimplemented on this machine

when use forkmanager by ruby .it happen this: ruby version: ruby 2.4.1p111 (2017-03-22 revision 58053) [x64-mingw32] system version: windows7 64 Uncaught exception: fork() function is unimplemented on this machine D:/Ruby24-x64/lib/ruby/gems/2.4.0/gems/parallel-forkmanager-2.0.1/lib/parallel/forkmanager.rb:525:in fork' D:/Ruby24-x64/lib/ruby/gems/2.4.0/gems/parallel-forkmanager- 2.0.1/lib/parallel/forkmanager.rb:525:instart'

#!/usr/bin/env ruby
#encoding: UTF-8
# 抓取每一个站点的首页链接数量

require 'rubygems'          
require 'ap'               
require 'json'
require 'net/http'
require 'nokogiri'         
require 'forkmanager'       
require 'beanstalk-client'  

class MultipleCrawler

    class Crawler
        def initialize(user_agent, redirect_limit=1)
            @user_agent = user_agent
            @redirect_limit = redirect_limit
            @timeout = 20
        end
        attr_accessor :user_agent, :redirect_limit, :timeout

        def fetch(website)
            print "Pid:#{Process.pid}, fetch: #{website}\n"
            redirect, url = @redirect_limit, website
            start_time = Time.now
            redirecting = false
            begin
                begin
                    uri = URI.parse(url)
                    req = Net::HTTP::Get.new(uri.path)
                    req.add_field('User-Agent', @user_agent)
                    res = Net::HTTP.start(uri.host, uri.port) do |http|
                        http.read_timeout = @timeout
                        http.request(req)
                    end
                    if res.header['location'] # 遇到重定向，则url设定为location，再次抓取
                        url = res.header['location'] 
                        redirecting = true
                    end
                    redirect -= 1
                end while redirecting and redirect>=0
                opened_time = (Time.now - start_time).round(4) # 统计打开网站耗时
                encoding = res.body.scan(/<meta.+?charset=["'\s]*([\w-]+)/i)[0]
                encoding = encoding ? encoding[0].upcase : 'GB18030'
                html = 'UTF-8'==encoding ? res.body : res.body.force_encoding('GB2312'==encoding || 'GBK'==encoding ? 'GB18030' : encoding).encode('UTF-8') 
                doc = Nokogiri::HTML(html)
                processed_time = (Time.now - start_time - opened_time).round(4) # 统计分析链接耗时, 1.8.7, ('%.4f' % float).to_f 替换 round(4)
                [opened_time, processed_time, doc.css('a[@href]').size, res.header['server']]
            rescue =>e
                e.message  
            end
        end
    end

    def initialize(websites, beanstalk_jobs, pm_max=1, user_agent='', redirect_limit=1)
        @websites = websites                # 网址数组 
        @beanstalk_jobs = beanstalk_jobs    # beanstalk服务器地址和管道参数
        @pm_max = pm_max                    # 最大并行运行进程数
        @user_agent = user_agent            # user_agent 伪装成浏览器访问
        @redirect_limit = redirect_limit    # 允许最大重定向次数

        @ipc_reader, @ipc_writer = IO.pipe # 缓存结果的 ipc 管道
    end

    attr_accessor :user_agent, :redirect_limit

    def init_beanstalk_jobs # 准备beanstalk任务
        beanstalk = Beanstalk::Pool.new(*@beanstalk_jobs)
        #清空beanstalk的残留消息队列
        begin
            while job = beanstalk.reserve(0.1) 
                job.delete
            end
        rescue Beanstalk::TimedOut
            print "Beanstalk queues cleared!\n"
        end
        @websites.size.times{|i| beanstalk.put(i)} # 将所有的任务压栈
        beanstalk.close
        rescue => e 
            puts e 
            exit
    end

    def process_jobs # 处理任务
        start_time = Time.now
        pm = Parallel::ForkManager.new(@pm_max)
        @pm_max.times do |i|
            # 启动后，立刻 next 不会等待进程执行完，这样才可以并行运算
            pm.start(i) and next 
            beanstalk = Beanstalk::Pool.new(*@beanstalk_jobs)
            # 关闭读取管道，子进程只返回数据
            @ipc_reader.close  
            loop{ 
                begin
                    # 检测超时为0.1秒，因为任务以前提前压栈
                    job = beanstalk.reserve(0.1) 
                    index = job.body
                    job.delete
                    website = @websites[index.to_i]
                    result = Crawler.new(@user_agent).fetch(website)
                    @ipc_writer.puts( ({website=>result}).to_json )
                rescue Beanstalk::DeadlineSoonError, Beanstalk::TimedOut, SystemExit, Interrupt
                    break
                end
            }
            @ipc_writer.close
            pm.finish(0)    
        end
        @ipc_writer.close
        begin
             # 等待所有子进程处理完毕 
            pm.wait_all_children 
            # 遇到中断，打印消息      
        rescue SystemExit, Interrupt    
            print "Interrupt wait all children!\n"
        ensure
            results = read_results
             # 打印处理结果
            ap results, :indent => -4 , :index=>false
            print "Process end, total: #{@websites.size}, crawled: #{results.size}, time: #{'%.4f' % (Time.now - start_time)}s.\n"
        end
    end

    def read_results # 通过管道读取子进程抓取返回的数据
        results = {}
        while result = @ipc_reader.gets
            results.merge! JSON.parse(result)
        end
        @ipc_reader.close
        results
    end

    def run # 运行入口
        init_beanstalk_jobs
        process_jobs
    end
end

websites = %w(
http://www.51buy.com/ http://www.360buy.com/ http://www.tmall.com/ http://www.taobao.com/
http://ift.tt/oX2ZfL http://www.paipai.com/ http://shop.qq.com/ http://ift.tt/GRfNbH
http://www.amazon.cn/ http://ift.tt/quKrsm http://www.vancl.com/ http://ift.tt/y9aO1u 
http://ift.tt/IAKFQ5 http://www.m18.com/ http://www.suning.com/ http://www.hstyle.com/
)

beanstalk_jobs = [['127.0.0.1:11300'],'crawler-jobs']
user_agent = 'Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/60.0.3112.113 Safari/537.36'
pm_max = 10

MultipleCrawler.new(websites, beanstalk_jobs, pm_max, user_agent).run