Fix Log deletion bug

[schneems]

A Tempfile works by defining a "finalizer" this is code that gets run when the object is cleaned up via GC. Here's a link:

https://github.com/ruby/ruby/blob/935d0b3d05dfc8b30bba505792129bf0e33ebe3b/lib/tempfile.rb#L132

As long as another object has a reference to a Tempfile then it will not be deleted from disk. In this scenario we're passing it to a Pathname object and it does not retain a reference to the passed in argument. You can reproduce this bug/behavior outside of Rundoc:

$ cat scratch.rb
require 'pathname'
require 'tempfile'

def make_pathname(value = Tempfile.new("log"))
  Pathname.new(value)
end

p = make_pathname
FileUtils.touch(p)

puts "File: #{p.file?}"

GC.start

puts "File: #{p.file?}"

This generates:

$ ruby scratch.rb
File: true
File: false

This PR fixes the behavior by forcing a reference to the Tempfile object in the top level ProcessSpawn instance instead of expecting the Pathname @log instance variable to hold its reference.

[chrisseaton]

What's with the http:// appearing in your code sample? That's not valid Ruby is it? It runs if I remove it.

[schneems]

Thats from me copying it from twitter which thinks Pathname.new is a link with new as the TLD. I updated it. You need to run it as a file. It runs, but the GC.start deletes the file, which happens randomly in the code and has taken my month figure out with a few hours of active debugging.