Async does not protect against array modifications during the function's runtime

When you have an asynchronous call eg. async.each, and during that runtime, the array which is passed in has modifications to it, then it may never finish, or will call the callback twice.

Example:

async = require "async" 
arr = [1, 2, 3]  
async.each arr, ((i, cb) -> console.log "i"; setImmediate(cb)), (err) -> console.log "done" 
arr.push(4)

This example loops through the 3 original array elements, and prints i but then never calls the callback, because in async.each it’s doing:

if (completed >= arr.length) {
  callback(null);
}

When looking at the async code, it’s doing a comparison against arr.length which can change…would it not be better to store the original array length and do a comparison against that, ensuring that the completed callback will be called?

Fiddle: http://jsfiddle.net/4ysKX/1/

[ORESoftware]

Did async end up disallowing array modifications after the fact? I have a use case where it would be nice to modify the original array after the fact, so as to iterate on more elements than initially.

[aearly]

This is a duplicate of #557.