pry-timetravel

Time travel! For your REPL!

> x = 5
5
> snap
> x = 10
10
> back
> x
5

This is an attempt to package the proof of concept. API WILL CHANGE!

The 'snap' command causes a fork, and the child is sent a SIGSTOP to freeze the process. The parent continues on. Later when you do 'back' the saved child is sent SIGCONT and the current process is sent a SIGSTOP. Ultimately you can have a whole pool of frozen snapshots and can resume any of them.

In theory copy-on-write semantics makes this a tollerable thing to do :)

There are a few more details, but that is the important bit.

WARNING: Time travel may cause zombies.

• If you close a connection, like to a DB, it is closed for all snapshots

Redis checks to see if you forked and yells at you about needing to reconnect. Reasonably so, as it is a crazy idea to use the same connection in forked children! But we are doing crazy things. In 3.1.0 the gem will auto-reconnect, or you can pass inherit_socket to the connection to stop that. Or you can do this to bypass safety measures:

class Redis
  class Client
    def ensure_connected
      yield
    end
  end
end

• Time Travel Python Debugger
• Elm's Time Traveling Debugger
• OCaml Time Travel
• Chronon (java - proprietary)

Released under the MIT license, see LICENSE.MIT for details. License is negotiable. Contributions and bug-reports are welcome!