From: acid06@...
Date: 2014-01-24T17:47:52+00:00
Subject: [ruby-core:60061] [ruby-trunk - Bug #9447] [Open] Bad interaction between Fibers and Trap handlers in Ruby > 2.0.0

Issue #9447 has been reported by Nilson Santos Figueiredo Junior.

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Bug #9447: Bad interaction between Fibers and Trap handlers in Ruby > 2.0.0
https://bugs.ruby-lang.org/issues/9447

* Author: Nilson Santos Figueiredo Junior
* Status: Open
* Priority: Normal
* Assignee: 
* Category: 
* Target version: 
* ruby -v: ruby 2.0.0p247
* Backport: 1.9.3: UNKNOWN, 2.0.0: UNKNOWN, 2.1: UNKNOWN
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Hi there,

I've been using and Alarm class I created, which gives Ruby code access to the alarm system call.
It used to work perfectly on 1.9.3 with no issues and more than 1 year of production usage.

Ruby 2.0.0 doesn't let me use it properly, apparently when there's an alarm timeout, the interpreter will think the code is in the trap context forever, so when I try to use Logger afterwards, it will fail (since it uses a Mutex internally).

Below is my Alarm implementation.

    require 'dl'
    require 'dl/import'

    module Alarm
      module SystemCall
        extend DL::Importer

        # imports the POSIX alarm function 
        begin
          dlload 'libc.so.6'
        rescue
          begin
            dlload 'libc.so.5'
          rescue
            dlload 'libc.dylib'
          end
        end
        extern 'unsigned int alarm(unsigned int)'
      end

      def self.alarm(n)
        # creates new fiber which will the code block passed as argument
        fiber = Fiber.new { yield }
        begin
          # new signal handler for the alarm call
          handler = Signal.trap('ALRM') do
            # yields fiber, which makes the control flow continue after
            # after the last resume call for this fiber
            # (in other words, returns from this function)
            Fiber.yield
          end
          # start timing
          SystemCall.alarm(n)
          # start running timed call
          result = fiber.resume
        ensure
          # cancel alarms and restore the previous signal handler
          SystemCall.alarm(0)
          Signal.trap('ALRM', handler)
        end
        return result
      end
    end

Is this sort of thing really no longer supported in Ruby > 2.0.0 or is it a bug? As I've said, it worked perfectly on 1.9.3.
This class is used like this:

    Alarm.alarm(timeout_seconds) do
      # potentially time consuming operation which must have a timeout
    end

Due to other requirements, I can't use the Timeout module, as it creates another thread.
Thanks in advance.



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