Issue #6647 has been updated by Koichi Sasada.


any conclusion?

Another idea:

(1) Thread#report_on_exception = true
Show exception and backlog immediately (already proposed)

(2) Thread#report_on_exception = false (default)
Show exception and backlog at GC timing if exception is not handled.

I agree (1) is preferable, but breaks compatibility.
I agree #54, if people specify all of threads (which are joined after) `report_on_exception = false` (or specify `report: false`) will solve this compatibility. But I'm not sure we can accept this approach.

(2) is not so good because the report will be delayed.
But not so bad compare with nothing to show.


----------------------------------------
Feature #6647: Exceptions raised in threads should be logged
https://bugs.ruby-lang.org/issues/6647#change-58865

* 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:

```ruby
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"   
```

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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