在 concurrent-ruby 线程池中处理异常

Question

如何处理并发-ruby线程池(http://ruby-concurrency.github.io/concurrent-ruby/file.thread_pools.html)中的异常？

示例：

pool = Concurrent::FixedThreadPool.new(5) 
pool.post do
  raise 'something goes wrong'
end

# how to rescue this exception here

更新：

这是我的代码的简化版本：

def process
  pool = Concurrent::FixedThreadPool.new(5)

  products.each do |product|
    new_product = generate_new_product

    pool.post do
      store_in_db(new_product) # here exception is raised, e.g. connection to db failed
    end
  end

  pool.shutdown
  pool.wait_for_terminaton
end

所以我想要实现的是在出现任何异常时停止处理（中断循环）。

这个异常也在更高级别的应用程序中被拯救并且执行了一些清理工作（比如将模型状态设置为失败并发送一些通知）。

Answer 1

可能有更好的方法，但这确实有效。您需要更改 wait_for_pool_to_finish 内的错误处理。

def process
  pool = Concurrent::FixedThreadPool.new(10)
  errors = Concurrent::Array.new

  10_000.times do
    pool.post do
      begin
        # do the work
      rescue StandardError => e
        errors << e
      end
    end
  end
  wait_for_pool_to_finish(pool, errors)
end

private

def wait_for_pool_to_finish(pool, errors)
  pool.shutdown

  until pool.shutdown?
    if errors.any?
      pool.kill
      fail errors.first
    end
    sleep 1
  end

  pool.wait_for_termination
end

Answer 2

以下回答来自jdantonio 来自这里https://github.com/ruby-concurrency/concurrent-ruby/issues/616

” 大多数应用程序不应该直接使用线程池。线程池是一种低级抽象，供内部使用。该库中的所有高级抽象（Promise、Actor 等）都 post 作业到全局线程池，并且都提供异常处理。只需选择最适合您的用例的抽象并使用它。

如果您觉得需要配置自己的线程池而不是使用全局线程池，您仍然可以使用高级抽象。它们都支持 :executor 选项，允许您注入自定义线程池。然后，您可以使用高级抽象提供的异常处理。

如果您绝对坚持 post 将作业直接发送到线程池而不是使用我们的高级抽象（我强烈反对），那么只需创建一个作业包装器。您可以在我们所有的高级抽象、Rails ActiveJob、Sucker Punch 和其他使用我们的线程池的库中找到作业包装器的示例。

那么用 Promises 实现怎么样？ http://ruby-concurrency.github.io/concurrent-ruby/Concurrent/Promise.html 在您的情况下，它看起来像这样：

promises = []
products.each do |product|
  new_product = generate_new_prodcut

  promises << Concurrent::Promise.execute do 
    store_in_db(new_product)
  end
end

# .value will wait for the Thread to finish.
# The ! means, that all exceptions will be propagated to the main thread
# .zip will make one Promise which contains all other promises.
Concurrent::Promise.zip(*promises).value!

Answer 3

我创建了一个问题 #634。并发线程池可以毫无问题地支持abortable worker。

require "concurrent"

Concurrent::RubyThreadPoolExecutor.class_eval do
  # Inspired by "ns_kill_execution".
  def ns_abort_execution aborted_worker
    @pool.each do |worker|
      next if worker == aborted_worker
      worker.kill
    end

    @pool = [aborted_worker]
    @ready.clear

    stopped_event.set
    nil
  end

  def abort_worker worker
    synchronize do
      ns_abort_execution worker
    end
    nil
  end

  def join
    shutdown

    # We should wait for stopped event.
    # We couldn't use timeout.
    stopped_event.wait nil

    @pool.each do |aborted_worker|
      # Rubinius could receive an error from aborted thread's "join" only.
      # MRI Ruby doesn't care about "join".
      # It will receive error anyway.

      # We can "raise" error in aborted thread and than "join" it from this thread.
      # We can "join" aborted thread from this thread and than "raise" error in aborted thread.
      # The order of "raise" and "join" is not important. We will receive target error anyway.

      aborted_worker.join
    end

    @pool.clear
    nil
  end

  class AbortableWorker < self.const_get :Worker
    def initialize pool
      super
      @thread.abort_on_exception = true
    end

    def run_task pool, task, args
      begin
        task.call *args
      rescue StandardError => error
        pool.abort_worker self
        raise error
      end

      pool.worker_task_completed
      nil
    end

    def join
      @thread.join
      nil
    end
  end

  self.send :remove_const, :Worker
  self.const_set :Worker, AbortableWorker
end

class MyError < StandardError; end

pool = Concurrent::FixedThreadPool.new 5

begin
  pool.post do
    sleep 1
    puts "we shouldn't receive this message"
  end

  pool.post do
    puts "raising my error"
    raise MyError
  end

  pool.join

rescue MyError => error
  puts "received my error, trace: \n#{error.backtrace.join("\n")}"
end

sleep 2

输出：

raising my error
received my error, trace:
...

此补丁适用于任何版本的 MRI Ruby 和 Rubinius。 JRuby 不工作，我不在乎。如果你想支持 JRuby executor，请打补丁。应该很简单。

在 concurrent-ruby 线程池中处理异常

Handle exceptions in concurrent-ruby thread pool

ruby

multithreading

concurrency

concurrent-ruby