1. Rather than just writing in the current directory, I think it'd be better to write in a named subdirectory (such as `child_backtraces`).
2. `File.write` is a new API in ruby 1.9.3.  Officially Qless supports 1.9+, which means it needs to support 1.9.2 where that's not available.  Instead you can use `File.open(filename, 'w') { |f| f.write(Marshal.dump(e)) }`.