如何优雅地关闭 Ruby 中的线程

Question

过去一周我一直在尝试 Ruby 中的多线程概念。

为了练习，我正在设计一个文件下载器，它对一组 URL 发出并行请求。目前我需要在触发中断信号时安全地关闭线程。我已经阅读了多线程和在运行时捕获信号的理论。然而，尽管有了这些理论知识，我仍然不知道如何在实践中使用它们。

无论如何，我将把我的概念验证工作留在下面。

class MultiThread
  attr_reader :limit, :threads, :queue

  def initialize(limit)
    @limit   = limit
    @threads = []
    @queue   = Queue.new
  end

  def add(*args, &block)
    queue << [block, args]
  end

  def invoke
    1.upto(limit).each { threads << spawn_thread }
    threads.each(&:join)
  end

  private

  def spawn_thread
    Thread.new do
      Thread.handle_interrupt(RuntimeError => :on_blocking) do
        # Nothing to do
      end

      until queue.empty?
        block, args = queue.pop
        block&.call(*args)
      end
    end
  end
end

urls = %w[https://example.com]
thread = MultiThread.new(2)

urls.each do |url|
  thread.add do
    puts "Downloading #{url}..."
    sleep 1
  end
end

thread.invoke

Answer 1

是的，handle_interrupt 的文档令人困惑。试试这个，我基于例如使用的connection_pool gem puma.

$stdout.sync = true

threads = 3.times.map { |i|
  Thread.new {
    Thread.handle_interrupt(Exception => :never) do
      begin
        Thread.handle_interrupt(Exception => :immediate) do
          puts "Thread #{i} doing work"
          sleep 1000
        end
      ensure
        puts "Thread #{i} cleaning up"
      end
    end
  }
}

Signal.trap("INT")  {
  puts 'Exiting gracefully'
  threads.each { |t|
    puts 'killing thread'
    t.kill
  }
  exit
}

threads.each { |t| t.join }

输出：

Thread 1 doing work
Thread 2 doing work
Thread 0 doing work
^CExiting gracefully
killing thread
killing thread
killing thread
Thread 0 cleaning up
Thread 1 cleaning up
Thread 2 cleaning up