Multithread IRB feature

[tompng]

Description

Running IRB in multiple thread won't work now.

Thread.new do
  sleep 2
  binding.irb
end
binding.irb

If it can, debugging multithread program might be easier.

PoC

I made a PoC https://github.com/tompng/irb/tree/thread_irb

Problem

• Is it maintainable?
• Does debug commands work? Wouldn't this feature slows down improving debug commands?
• Can it be integrated well with workspace commands?

[st0012]

Since debug has better control over threads (th commands), maybe the direction could be to utilise it? irb:rdbg doesn't work with the example atm though.