Issue #6647 has been updated by Lin Jen-Shin.


Not sure if a +1 would do anything, but I like the idea of
`Thread#report_on_exception` defaults to true.

For quick and one time scripts, it's tedious to write
`Thread.current.abort_on_exception = true` all the time,
and it shouldn't be set to true by default, either.
So at least make debugging easier by default is a good idea,
and who doesn't like to see warnings anyway? :P

I was referred from yahns mailing list:
http://yhbt.net/yahns-public/m/20150508170311.GA1260%40dcvr.yhbt.net.html
Which some worker threads were dead silently and it's puzzling
if I don't even know there's an exception was raised.

----------------------------------------
Feature #6647: Exceptions raised in threads should be logged
https://bugs.ruby-lang.org/issues/6647#change-52352

* Author: Charles Nutter
* Status: Assigned
* Priority: Normal
* Assignee: Yukihiro Matsumoto
----------------------------------------
Many applications and users I have dealt with have run into bugs due to Ruby's behavior of quietly swallowing exceptions raised in threads. I believe this is a bug, and threads should always at least log exceptions that bubble all the way out and terminate them.

The implementation should be simple, but I'm not yet familiar enough with the MRI codebase to provide a patch. The exception logging should be logged in the same way top-level exceptions get logged, but perhaps with information about the thread that was terminated because of the exception.

Here is a monkey patch that simulates what I'm hoping to achieve with this bug:


class << Thread
  alias old_new new

  def new(*args, &block)
    old_new(*args) do |*bargs|
      begin
        block.call(*bargs)
      rescue Exception => e
        raise if Thread.abort_on_exception || Thread.current.abort_on_exception
        puts "Thread for block #{block.inspect} terminated with exception: #{e.message}"
        puts e.backtrace.map {|line| "  #{line}"}
      end
    end
  end
end

Thread.new { 1 / 0 }.join
puts "After thread"   

__END__

Output:

system ~/projects/jruby $ ruby thread_error.rb 
Thread for block #<Proc:0x000000010d008a80 / thread_error.rb:17> terminated with exception: divided by 0
  thread_error.rb:17:in `/'
  thread_error.rb:17
  thread_error.rb:7:in `call'
  thread_error.rb:7:in `new'
  thread_error.rb:5:in `initialize'
  thread_error.rb:5:in `old_new'
  thread_error.rb:5:in `new'
  thread_error.rb:17
After thread




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