Mitosis

Short description

Mitosis allows Go applications to easily fork themselves while preserving arbitrary application state and inherit file descriptors. In this context, 'arbitrary' means: anything you can marshal into a byte slice.

Longer description

Mitosis supplies a simple mechanism by which any Go application can have itself relaunched into a new session, while allowing it to pass on arbitrary application state to the new instance. This includes inheritance of open file descriptors.

Any aplication wanting to hook into this service, must import this package, and implement the API it exposes. An example of this can be seen in testdata/main.go.

Why?

I wrote this because I have several long running applications which need to be updated occasionally. One of which is an IRC bot. Its functionality consists of plugin modules. Because Go does not support hit-plugging of code, I am relegated to recompiling the bot, stopping the original and relaunching it.

This naturally means it will lose its connection to the IRC server. Not only does this generate JOIN/PART noise in the channels it occupies, it is simply unnecessary if I am able to launch a new bot instance, hand it the existing connection and then gracefuly shut down the original.

This is what Mitosis seeks to offer in a generalized plug-and-play fashion.

Technical bits

The steps involved are roughly as follows:

• Application is launched:

  • Call mitosis.Init(): Check if the current session was launched by mitosis. If so, it has gotten the -mitosis=xxxx commandline parameter. This holds the port number on which the previous session is listening for TCP connections.
  • Connect to this port number and fetch application state from the old session. It is passed into a callback function you specify. At this point, it is up to you to decide what to do with this state data.
  • We disconnect from the server and hand control back to your code.

• Application wants to fork itself and does so by calling mitosis.Split().

  • Mitosis sets up a TCP listener on a random, free port.
  • It executes its own binary, passing it any commandline arguments which are specified in the mitosis.State structure as well as the -mitosis flag, which holds the port number on which it is listening.
  • It waits for the new instance to connect to it.
  • Performs some /very/ rudimentary protocol verification.
  • Sends the current application state to the new instance and disconnects.
  • The application is now notified of successful forking by means of a boolean channel. Once this channel is triggered, the application will know it is safe to shut itself down.

Usage

$ go get github.com/jteeuwen/mitosis

License

Unless otherwise stated, all of the work in this project is subject to a 1-clause BSD license. Its contents can be found in the enclosed LICENSE file.