Contain async insanity so that the dark pony lord doesn't eat souls
See this blog post.
Pass a callback to dezalgo and it will ensure that it is always
called in a future tick, and never in this tick.
var dz = require('dezalgo')
var cache = {}
function maybeSync(arg, cb) {
cb = dz(cb)
// this will actually defer to nextTick
if (cache[arg]) cb(null, cache[arg])
fs.readFile(arg, function (er, data) {
// since this is *already* defered, it will call immediately
if (er) cb(er)
cb(null, cache[arg] = data)
})
}